Feld Hell Motor Generator Overhaul

Overhaul of the Hell Feldfernschreiber Motor-Generator

Overhaul of the Hell Feldfernschreiber

Motor-Generator

by Frank M.G. Drenberg, N4SPP

The author does not assume any liability for correctness of the descriptions and instructions contained herein, nor for any damages that may result from following the instructions. All rights reserved world wide.

Version 1.1, 23 May 2009 1 2009 Frank M.G. Drenberg, N4SPP Restrictions stated on the cover page apply. www.nonstopsystems.com/hell.htm


CONTENTS

Page

LIST OF APPENDICES....................................................................................................................... 2 LIST OF FIGURES............................................................................................................................. 3 LIST OF FIGURES............................................................................................................................. 3 INTRODUCTION............................................................................................................................... 5 GENERAL RULES .............................................................................................................................. 7 Required tools, materials and components ......................................................................................... 7 Literature references ........................................................................................................................ 9 OVERVIEW OF THE TASKS.............................................................................................................. 10

Task 1 remove the Motor-Generator from the Bottom-Unit of the Hellschreiber......................... 11 Task 2 remove the carbon brushes of the generator ............................................................... 12 Task 3 remove the tappet and ball bearing shield at bottom of the generator ........................... 13 Task 4 remove the speed adjustment cap and dial at the top of the motor ............................... 14 Task 5 remove the contact plate above the centrifugal speed regulator.................................... 15 Task 6 remove the centrifugal speed regulator from the top of the Motor-Generator shaft ......... 19 Task 7 take the motor carbon brush clips off their pin ............................................................ 24 Task 8 take apart the Motor-Generator housing and remove the rotor...................................... 27

Planning the next steps .................................................................................................................. 33 Task 9 assess the surface of the carbon brushes and commutators.......................................... 34 Task 10 remove the motor and generator ball bearings .......................................................... 37 Task 11 mount new ball bearings.......................................................................................... 40 Task 12 refurbish the capacitors ........................................................................................... 44 Task 13 reinstall the motor carbon brushes............................................................................ 47 Task 14 perform installation of a single bearing shield washer................................................. 51 Task 15 reinstall the rotor and generator bearing shield washers ............................................. 52 Task 16 reinstall the top of the housing and motor bearing shield washers ............................... 55 Task 17 reinstall the housing bracket and hexagonal studs...................................................... 56 Task 18 reinstall the centrifugal speed regulator .................................................................... 57 Task 19 reinstall the contact plate......................................................................................... 58 Task 20 reinstall the speed adjustment dial............................................................................ 60 Task 21 reinstall the carbon brushes of the generator............................................................. 61 Task 22 reinstall the tappet on the motor output shaft............................................................ 62 Task 23 power up and test run of the Motor-Generator........................................................... 62 Task 24 calibrate the speed set point of the speed regulator ................................................... 64 Task 25 mount the Motor-Generator back on the Bottom Unit ................................................. 68 Task 26 reinstall the black plastic speed regulator cap and drum cover .................................... 70 Task 27 reinstall the cover box on the back of the motor-generator ......................................... 70 Task 28 perform the final operational test ............................................................................. 71

CONCLUSION ................................................................................................................................ 71

LIST OF APPENDICES Page

Appendix 1 Assessment of carbon brush surface appearance................................................... 72 Appendix 2 Assessment of commutator surface appearance ..................................................... 73 Appendix 3 Abnormal bearing sound characteristics and related factors.................................... 74 Appendix 4 Ball bearings and their (dis)mounting ................................................................... 75 Appendix 5 Capacitors.......................................................................................................... 78 Appendix 6 General cleaning................................................................................................. 86 Appendix 7 Strobe disks ....................................................................................................... 87 Appendix 8 Diploma............................................................................................................. 88



LIST OF FIGURES

Page

Figure 1 Simplified cross-section of the Motor-Generator ...........................................................6 Figure 2 Most of the tools that I used for this project ................................................................8 Figure 3 Rear of the Motor-Generator with cover box .............................................................. 11 Figure 4 Location of the generator's carbon brushes................................................................ 12 Figure 5 One of the generator's carbon brushes and its brush holder cap.................................. 12 Figure 6 Output shaft - before and after removal of the tappet ................................................ 13 Figure 7 Bottom of generator ball bearing tappet and shield washer removed......................... 13 Figure 8 Tappet, bearing shield washer and associated screws................................................. 14 Figure 9 The speed regulator adjustment ring - disassembled .................................................. 15 Figure 10 Contact plate before disassembly ........................................................................... 16 Figure 11 Cross-section of the centrifugal speed regulator ......................................................... 17 Figure 12 The regulator disk is visible after removal of the contact plate ..................................... 17 Figure 13 Contact plate top and bottom view........................................................................ 18 Figure 14 Contact plate side views ........................................................................................ 18 Figure 15 Filter capacitor C68.................................................................................................. 19 Figure 16 Access to the screw that secures the speed regulator disk........................................... 20 Figure 17 The centrifugal weight mechanism atop the motor shaft ............................................. 20 Figure 18 Centrifugal regulator side views ............................................................................. 21 Figure 19 Centrifugal regulator top and bottom view .............................................................. 22 Figure 20 Top of motor housing regulator removed, bearing shield visible ................................ 22 Figure 21 The motor bearing shield, with bushing and wavy spring washer ................................. 23 Figure 22 Top of motor housing ball bearing shield removed................................................... 23 Figure 23 JAHRELYT capacitors from Richard Jahre GmbH and 1942 advertising.......................... 24 Figure 24 Lead-wire of the +12 VDC motor carbon brush .......................................................... 25 Figure 25 Lead-wire of the -12 VDC motor carbon brush............................................................ 25 Figure 26 Access to one of the motor carbon brush clips ........................................................... 26 Figure 27 The motor carbon brush clips and springs.................................................................. 26 Figure 28 Top ends of the mounting rods ................................................................................. 27 Figure 29 Bottom ends of the mounting rods ............................................................................ 28 Figure 30 Motor-Generator housing with bracket....................................................................... 28 Figure 31 Motor-Generator housing bracket.............................................................................. 29 Figure 32 Hexagonal guide-pin studs and associated springs...................................................... 29 Figure 33 Motor-Generator housing separated, rotor removed................................................. 30 Figure 34 Rotor of the Motor-Generator with ball bearings and shields........................................ 31 Figure 35 Filter components and carbon brush attachment points............................................... 31 Figure 36 Looking down into the base of the generator ............................................................. 32 Figure 37 The disassembled items ........................................................................................... 33 Figure 38 Sliding face of the generator carbon brushes ............................................................. 34 Figure 39 Sliding face of the motor carbon brushes ................................................................... 35 Figure 40 Commutator of the Motor......................................................................................... 36 Figure 41 Commutator of the Generator................................................................................... 36 Figure 42 Rotor of the Motor-Generator and bearing shields bearings removed......................... 38 Figure 43 Bearing pullers and a bearing splitter ........................................................................ 39 Figure 44 Limited space for bearing puller between bearings and commutators ........................... 39 Figure 45 My new ball bearings in standard packaging............................................................ 40 Figure 46 A small arbor press and the cross-section of a drift..................................................... 42 Figure 47 Rings of discarded bearings can be used as drifts ....................................................... 42 Figure 48 Using a drill press, vise, and bearing ring drifts .......................................................... 43 Figure 49 Schematic around generator filter capacitors C64 and C65 .......................................... 45 Figure 50 Paper capacitor C64 (top) and C65 (bottom).............................................................. 45



Page

Figure 51 Schematic around C62, C63, and C66........................................................................ 46 Figure 52 Schematic around C67 ............................................................................................. 46 Figure 53 Motor-Generator interconnect panel .......................................................................... 47 Figure 54 Motor turning direction and carbon brush clip installation............................................ 48 Figure 55 Carbon brush clips of the motor put back onto their pins............................................. 48 Figure 56 Paperclip retainers for the motor carbon brush clips ................................................... 49 Figure 57 Dimensions of the paperclip retainers ........................................................................ 49 Figure 58 Carbon brush clips retained with paperclips................................................................ 50 Figure 59 Attachment of the retainer clips on the outside of the housing..................................... 51 Figure 60 My tap & die set and a bar-wrench with tap............................................................... 52 Figure 61 Identification of the motor and generator end of the rotor .......................................... 53 Figure 62 Paperclip folded into hairpin ..................................................................................... 53 Figure 63 The rotor - put back into the base of the housing....................................................... 54 Figure 64 Hole in shaft - for mounting screw of speed regulator disk .......................................... 57 Figure 65 Alignment and push points of the contact plate .......................................................... 60 Figure 66 Alignment of carbon brush and commutator............................................................... 61 Figure 67 Shape of the generator's carbon brush holders........................................................... 61 Figure 68 Location of the sparks at the K2 contact .................................................................... 63 Figure 69 Circuit continuity measurement points ....................................................................... 64 Figure 70 Optical tachometer (prototype and "wand" version) and schematic .............................. 65 Figure 71 Oscilloscope indicating 3600 rpm (240 Hz, 4-segment strobe disk)............................... 65 Figure 72 Feld-Hell on the operating table, strobe disk attached to motor output shaft................. 66 Figure 73 Centrifugal regulator with set screw .......................................................................... 67 Figure 74 Access to the speed regulator adjustment set screw ................................................... 67 Figure 75 Bottom view of the Motor-Generator (left) and top of the gear-box (right).................... 69 Figure 73 A typical non-shielded ball bearing ............................................................................ 75 Figure 74 Open, shielded, and sealed ball bearing (left to right) and cross-section ....................... 76 Figure 75 Characteristics of several capacitor types................................................................... 81 Figure 76 Using heat to remove a paper capacitor from its potted tube...................................... 83 Figure 77 Paper capacitors freed from their tar-potted cardboard tube........................................ 83 Figure 78 A paper capacitor freed from its tar-potted plastic tube............................................... 84 Figure 79 Strobe disks with 2, 4 and 8 segments ...................................................................... 87



INTRODUCTION Sooner or later in the life of any Hell Feldfernschreiber, there comes a time that maintenance must be done (or be contemplated) on the motor-generator. This was the case with my own Feld-Hell machine, serial number 3386, built in 1938. The immediate reason was a worrisome shrill, dry metal-on-metal noise that emanated from the top part of the motor-generator, as well as unexplained rpm reductions. To check running noise, the sound can be amplified and the type of noise ascertained with a listening instrument placed against the housing of the motor-generator (e.g., a large screwdriver don't stick the blade in you ear ). A clear, smooth and continuous running sound is normal. A light whirring sound is perfectly normal for electric motors, and stops as soon as power is removed (even though the machine is winding down). A high pitched, metallic or irregular sound indicates some error in function.

if the noise continues after power removal, it is mechanical and there may be cause for concern. Not wanting to do irreparable damage, I decided to not operate the machine until this problem was corrected. There is a Maintenance & Operating Manual from 1941 (ref. 1). This is a field manual. Regarding the Motor-Generator, it covers replacement of the carbon brushes, lubrication of an easily accessible part of the speed regulator, replacement of the contact plate above the speed regulator, and adjustment of the set point for the speed regulator. The Manual states that all other maintenance and repair actions are explicitly beyond field maintenance and shall be done by a qualified teleprinter fine-mechanic who has received special training on Hellschreibers. Such mechanics are hard to come by these days! So we will consider ourselves qualified by reason of our affection for Hellschreibers, do the required special training "on the job", and issue ourselves a diploma - upon successful completion (see appendix 8)! Note that the 1941 Manual says "The ball bearings of the motor-generator shall not be replaced." Well, at least not as part of field maintenance! This 1941 Manual also says "Every 100 operating hours, but at least every 8 weeks, the Feldfernschreiber must be oiled and greased." This includes the ball bearings of the gear-box and the character drum. Most of these bearings turn at a speed that is lower than that of the Motor-Generator's bearings, so you can imagine the latter definitely need maintenance. Furthermore, in ref. 3 it is stated that "Grease should not be allowed to remain in a bearing for more than 4 years, or if service is very light and temperatures low, 5 years, irrespective of the number of hours' operation during that period, as separation of the oil from the soap and oxidation continue whether the bearing is in operation or not." So, even if the bearings in your machine are not (yet) making any scary noises, it is probably a good idea to perform the overhaul anyway. This document captures and illustrates the steps that I followed to disassemble the motor-generator, replace the ball bearings, replace capacitors, perform lubrication, re-assemble the motor-generator, and perform final adjustments and test. I am generally opposed to all dogmas, so do not interpret the content of this manual as "the only way". Special thanks go to Arthur Bauer, PAAOB, for his expert advice and moral support. I intended this document to be the kind of manual I wished I had when I started the overhaul. Should you find this document in any way incorrect, incomplete, or otherwise in need of improvement, please do not hesitate to contact me ( ).

73 de Frank Drenberg, N4SPP



Figure 1 Simplified cross-section of the Motor-Generator

(motor and generator field windings not shown)



GENERAL RULES You are about to operate on a piece of history, possibly a museum piece! Here are some simple rules to observe:

1. Read this document at least once. 2. Do not rush! 3. Easy does it do not brute-force anything! 4. Careful when manipulating wires the original insulation tends to be brittle after all these years, as do

some of the electronic components. 5. Use the correct tools: right size, no screwdrivers with worn/rounded blades, no pliers, etc. 6. Retain originality to the extent possible:

Do not make modifications that are not 100% reversible. When electronic components need to be replaced: leave the original in place and disconnect

only one of the lead-wires (insulate with shrink tube or cloth tube if necessary), install the replacement component (typically much smaller) across the original.

When mechanical components need to be replaced (ball bearing, screws, etc.), keep the old ones.

Non-aggressive cleaning is OK, but touching up the paint is not. 7. Only use acid-free lubricants. 8. When in doubt, ask!

Required tools, materials and components Required tools and materials:

Screw driver appropriate for M5 screws. Screw driver appropriate for M3 screws. Screw driver with wide blade, for speed setting adjustment. Small 6 mm open-ended wrench, or an equivalent small adjustable wrench (referred as "spanner" in

the UK, "English key" in France, Germany, Holland, and "Swedish key" in Denmark). Soldering iron (not a soldering gun!) best is a medium sized one, with a controlled tip temperature

(400-425 C, 750-800 F). Solder wick. Use fresh instead of years old wick: it is ineffective when the braid has started to oxidize. Small plastic bags (e.g., small size Ziploc bags) to keep disassembled components organized. M3 x 20 mm screw (temporarily needed during re-assembly). Sewing machine oil (this is inexpensive, so go with a major brand sewing machines). A pair of wooden or hard plastic chopsticks (oriental eating sticks). A small bearing puller and bearing splitter (see Task 10). A non-slip mat, to protect your work bench or the table (esp. if you are doing this job on the dining

room table, like I did) and to protect disassembled and replacement parts (esp. ball bearings). A large, thick mouse pad may do.

Clean, lint-free cloth. Toothbrush, for general cleaning inside the housing.

Pliers are not on this list: they always cause damage. They should not be used on anything that you care about! To turn or hold screws and nuts, use a properly sized wrench. Required replacement components:

2 new ball bearings of type 627 "double shielded" (Z, ZZ, or 2Z, depending on the manufacturer). They should not have been sitting on the shelf for years and not come from somebody's junk box.

2 new axial-lead electrolytic capacitors 12 F (22 F is OK), at least 25 volt rating (pref. 35 V). 2 new axial-lead electrolytic capacitors 10 F, at least 25 volt rating.



Figure 2 Most of the tools that I used for this project

(bearing puller and splitter not shown; ref. Figure 43) Optional/recommended tools:

capacitor checker or capacitance meter (I used a Wavetek 2015 digital multimeter, capable of capacitance measurement).

Hemostat (a surgical tool which resembles a pair of needle nosed pliers with a locking clamp). They come in handy in many projects! See Figure 2, to the right of the black/yellow screwdrivers.

Calipers. Old-fashioned pink typewriter or ink eraser (to clean the commutators, if necessary). Small flashlight (UK: "torch") with fresh batteries. Jeweler's loupe (small magnifying glass that is set in an eye piece). Reading glasses (they may actually not be optional ). Tachometer for motor speed calibration (I prefer using a simple/cheap home-built optical tachometer

(circuit diagram is provided as part of Task 24) and an oscilloscope). Recommended replacement components:

2 new axial-lead capacitors (e.g., polypropylene), 270 nF, at least 630 volt rating. Several M3 screws (various lengths, flathead; to replace missing screws, if any). Several replacement M3 flat washers (to replace missing washers, if any). Several replacement M3 lock washers (star or split type; to replace missing washers, if any).



Literature references Ref. 1a: the 1941 Operating & Maintenance Manual "Der Hell Feldfernschreiber", document D 758/1 Ref. 1b: "The Hell Feldfernschreiber", translation of Ref. 1a into English by me, Frank Drenberg N4SPP Ref. 2: "The Feldfernschreiber Model 24a 32: list of components, annotated circuit card layout, connector

pin-outs, complete circuit diagram", 2008, by me. These documents are available from the "articles/literature" and the "maintenance" page of my Hellschreiber website, www.nonstopsytems.com/hell.htm. Ref. 3: pp. 2337-2340 in "Machinery's Handbook: A Reference Book for the Mechanical Engineer, Designer,

Manufacturing Engineer, Draftsman, Toolmaker, and Machinist", by Oberg, Jones, Horton, McCauley, Ryffel, Heald, Hussain, 27th ed., Industrial Press, 2004, ISBN 0831127007

Ref. 4: "NTN Rolling Bearings Handbook", Cat. No. 9012/E, 83 pp., available on-line from NTN CorporationRef. 5: "PanTrac Carbon Brushes for Industrial and Railway Technology", Ver. 1e/7-03; available on-line

from Pantrac GmbHRef. 6: "Commutator Surface Conditions" available on-line from Morgan Industrial CarbonRef. 7: "Assessment of Performance of Carbon Brushes" by Engineering Carbon ProductsRef. 8: "Handling and Mounting Precision Ball Bearings", MMG 7/94, available on-line from Barden Precision

Bearings (BPB)Ref. 9: "Carbon brushes - Frequently Asked Questions", SKT/GB4, available on-line at Schunk

Kohlenstofftechnik GmbH Note: hyperlinks in the above references were verified to be correct at the time this document was written.



OVERVIEW OF THE TASKS This job of disassembling the Motor-Generator of the Feld-Hell machine can be broken down into the following tasks:

1. Remove the Motor-Generator from the Bottom-Unit of the Hellschreiber. 2. Remove the carbon brushes of the generator. 3. Remove the tappet and ball bearing shield at bottom of the generator. 4. Remove the speed adjustment cap and dial at the top of the motor. 5. Remove the contact plate above the centrifugal speed regulator. 6. Remove the centrifugal speed regulator from the top of the Motor-Generator shaft. 7. Take the motor carbon brush clips off their pin.

Only after completing all these steps can the Motor-Generator housing be taken apart, and the rotor (with its top and bottom ball bearing) be removed!

8. Take apart the Motor-Generator housing and remove the rotor. 9. Assess the surface of the carbon brushes and commutators. 10. Remove the motor and generator ball bearings. 11. Mount new ball bearings. 12. Refurbish the capacitors.

Reassembly is basically done in reverse order of the disassembly:

13. Reinstall the motor carbon brushes. 14. Perform installation of a single bearing shield washer. 15. Reinstall the rotor and generator bearing shield washers. 16. Reinstall the top of the housing and motor bearing shield washers. 17. Reinstall the housing bracket and hexagonal studs. 18. Reinstall the centrifugal speed regulator. 19. Reinstall the contact plate. 20. Reinstall the speed adjustment dial. 21. Reinstall the carbon brushes of the generator. 22. Reinstall the tappet on the motor output. 23. Power up and test run of the Motor-Generator. 24. Calibrate the speed set point of the speed regulator. 25. Mount the Motor-Generator back on the Bottom Unit. 26. Reinstall the black plastic speed regulator cap and drum cover. 27. Reinstall the cover box on the back of the motor-generator.

Once this is all done, we can

28. Perform the final operational test.

Throughout this document, line items marked with 10 require special attention, as it is easy to do permanent damage. All task steps are marked with a check-box, so that you can check them off as you progress . 9

8



Task 1 remove the Motor-Generator from the Bottom-Unit of the Hellschreiber This task is described in line item 119 a) of the Manual, and is trivial:

Remove the Mechanical Unit from the case, and remove the protective cover of the drum. Remove the cover on the rear of the motor-generator, after loosening its mounting screw. Then remove the four mounting bolts (marked with a red ring) at the base of the generator, and carefully remove the motor-generator.

Undo the mounting bolt of the Amplifier-Interconnect Unit of the Feld-Hell machine, and partly pull

this unit out of the Feld-Hell case. Disconnect the two rectangular 6-pin connectors on the left hand side of this Unit (note: this cannot

be done unless this Unit is at least partially pulled out of the case). Release the latch lever of the Mechanical Unit, and slide this unit completely out of the case. Loosen the knurled two red knurled-head screws of the cover of the character drum, and remove the

cover. There is a rectangular protective cover on the rear of motor-generator; undo its mounting screw (M3

x 7 mm, countersunk-head with 5 mm diameter) and remove the cover. Put this mounting screw and the protective cover in small bag nr. 1. Undo the 4 mounting machine screws (M5 x 18 mm) at the base of the motor-generator Put these mounting screws in small bag nr 1. Lift the Motor-Generator off its base of the Bottom Unit.

Figure 3 Rear of the Motor-Generator with cover box



Task 2 remove the carbon brushes of the generator This step is described in line item 31 of the Manual, and is trivial. The high-voltage generator has two carbon brushes. They are located at the base of the motor-generator. One at the front (marked with and ), the other at the rear (marked with +).

Unscrew the black plastic cap of each carbon brush holder. Gently pull each carbon brush out by its spring-lead. Check the general condition of the carbon brushes, and make sure that they are still at least 6 mm

long ("). If not, you will have to find replacements.... Put the carbon brushes and the brush holder caps in small bag nr 2.

Front of the unit: the carbon brush for 165 VDC return Back of the unit: the carbon brush for +165 VDC

Figure 4 Location of the generator's carbon brushes

Figure 5 One of the generator's carbon brushes and its brush holder cap



Task 3 remove the tappet and ball bearing shield at bottom of the generator

This task is not described in the 1941 Manual. However, the task is trivial.

With an appropriately sized (6 mm) open wrench or a small adjustable wrench, remove the M3 x 6 mm screw (with 6 mm hexagonal head) that attaches the tappet to the motor shaft.

Pull the tappet off the motor shaft by its ends. o If the fit is tight, this also allows some gentle wiggling and prying.

Remove the three screws (M3 x 11 mm) of the shield washer, and remove the washer (34 mm outer diameter, 12 mm inner diameter, 1 mm thick).

Put the screws and washers, the tappet, and the shield washer in small bag nr. 3. The generator's ball bearing is now exposed.

Figure 6 Output shaft - before and after removal of the tappet

Figure 7 Bottom of generator ball bearing tappet and shield washer removed



Figure 8 Tappet, bearing shield washer and associated screws

Task 4 remove the speed adjustment cap and dial at the top of the motor

This step is described with sufficient detail as line item 120 of the 1941 manual:

Remove the index pointer of the motor speed adjustment tape-scale, after undoing the two mounting screws. Remove the regulator cap with its tape-scale by turning the cap counter- clockwise.

Remove the 2 screws (M3 x 5 mm; 5.5 mm oval head) of the speed dial index marker. Remove the marker itself. Put the screws and the marker index into (small) separate bag nr. 4. Unscrew the regulator cap (speed dial with black plastic cap) counter-clockwise until it comes off the

top of the motor. Starting with the speed dial set to 5, this takes a little more than 2 turns. Contrary to the 1941 Manual, we will remove the black plastic cap from the dial ring. The reason for this is that this we need a way to manually turn the rotor after the Motor-Generator has been completely re-assembled and installed back on the Bottom Unit (see Task 25). We do not want to power up the motor to find out whether the pin coupling to the gear-box has been mated correctly!

Remove the four machine screws (M3 x 6 mm, button-head) of the black plastic speed regulator cap Remove the plastic cap from the speed dial ring

o There is a thin aluminum (UK: aluminium) cover disk between the plastic cap and the dial ring. The bottom of this disk has a thin disk riveted to it, that looks like it is made out of pertinax or similar resin laminate material.

o The inside of the black plastic cap has a small marking T-typ. 58: the official Siemens-Halske designation for this type of teleprinter equipment.



Pull out the metal spacer ring that is inserted around the contact plate inside the top of the motor-generator.

o This is ring made of flat band metal (H = 8.5 mm ( 31 ), diameter = 90 mm (3)) Put bag nr. 3, the regulator cap, and the spacer ring into separate bag nr 4.

speed dial index marker speed regulator cap cover plate (upside down) spacer ring

Figure 9 The speed regulator adjustment ring - disassembled

Task 5 remove the contact plate above the centrifugal speed regulator

The contact plate is a basically a large, thin washer (OD = 92 mm, ID = 58 mm; 3" and 2" respectively). It is suspended above the centrifugal speed regulator disk by two cylindrical springs on guide pins. As shown in Figure 10 below, the two speed regulator spring-contacts are attached to the contact plate; as the motor speed changes, the contacts are moved up & down by a small rectangular piece of Turbax or Harex. This is a so-called "Hartgewebe", a cotton-reinforced laminate of thermosetting material (phenol-formaldehyde (PF) resin, similar to Bakelite). The lever of the centrifugal speed has a small ball (from a ball bearing) that is placed on the centerline of the rotor shaft. The ball remains centered when the tip of the lever moves up & down with speed changes. Movement of the lever is transferred to the Turbax piece via the ball. Note that the ball is captive, so you cannot loose it when the contact plate and the centrifugal speed regulator are removed . The contact plate also holds inductors and capacitors that suppress contact arcing and associated EMI.



This task is described in line item 120 a) of the 1941 Manual:

De-solder the wires from the terminals (items 3, 4 and 5 in Figure 10 below), and unscrew the two clips (items 6 and 7). After loosening the two screws (item 8 and 9), remove the contact plate.

It is easier to de-solder the wires when the clips are removed first, so that's what we'll do:

Remove the screws (M3 x 4 mm, flat-head) from the two wire clips and remove the clips. De-solder the three designated wires from their respective terminal lug.

The contact plate is held in place laterally by two short mounting screws; they are threaded into vertically installed guide pins (items 9 in Figure 11). The contact plate is spring-loaded by cylindrical springs on these guide pins. They push the contact plate upward against its mounting screws. The plate can be moved down by turning the cap of the speed regulator. You can (carefully) push down on the contact plate, right near its mounting screws it is fairly wobbly.

Remove the screws (M3 x 6 mm, flathead; item 8 and 9 in Figure 10 below) that hold down the contact plate.

Note that as soon either screw is removed, the plate pops up on that side, due to the loading springs on the guide pins underneath the contact plate.

Remove the contact plate. Put the contact plate, its mounting screws, the clips and their mounting screws in a small separate

bag nr. 5.

3 4

5

6 7

8

9

Figure 10 Contact plate before disassembly

The dark reddish-brown "spaghetti" wire insulation tubes (sleeves) are "lackgetrnkter Gewebe-Isolierschlauch" made of varnish-impregnated cotton or linen cloth ("lleinen"). The varnish used in this application is typically a derivative of linseed oil or shellac (a resin secreted by the female lac bug). The latter is relatively inflexible.



9 (ref. Fig. 9)8

(ref. Fig. 9)

ball

Turbax piece

Figure 11 Cross-section of the centrifugal speed regulator

ball

Figure 12 The regulator disk is visible after removal of the contact plate



Figure 13 Contact plate top and bottom view

Figure 14 Contact plate side views



The black filter capacitor in Figure 13 and 14 is 2000 pF, 500/1500 Vdc (operating/max) was manufactured by Richard Jahre GmbH, Spezialfabrik fr Kondensatoren, Induktivitten und Glimmerplatten, of Berlin (still in the capacitor business today). This capacitor corresponds to C68 in the schematic. Its cylindrical housing measures 26 mm in length x 8 mm diameter ( 1 x 31 ). The housing is a black plastic tube; the actual capacitor is inside, potted with a tar-like substance. Over the years, the value of this capacitor in my machine had increased from its nominal 2nF to 14 nF.

Figure 15 Filter capacitor C68 During a previous overhaul, capacitor C69 had already been replaced with the flat light yellow capacitor visible in Figure 13 and 14 above. It is a modern polycarbonate 3300 pF, 20%, 1000 volt made by ERO. I have replaced both with new 630 volt polypropylene capacitors. Ref. Appendix 5 regarding replacing and rebuilding capacitors. The accompanying filter inductors are D72 and D73, where "D" stands for "Drossel": choke coil. They are marked 191 and 192 in Figure 10 and 13. The schematic does not list their value, and the digital multi-meter that I had at my disposal does not measure inductance.

Task 6 remove the centrifugal speed regulator from the top of the Motor-Generator shaft

The centrifugal regulator assembly is basically a disk or flange that sits on top of the rotor shaft. The shaft smoothly fits into a hub or collar at the bottom of the disk. The disk is secured to the shaft with an M3 x 10 mm screw that goes completely through the rotor shaft; the (lock)washer has an outer diameter of 6 mm. This securing screw is only accessible through one hole in the motor housing. It is located just above the + marking of the motor carbon brush, See Figure 16 below.

Line item 101 of the 1941 Manual says:

The accuracy of the regulator can only be retained with careful treatment. Removal of the regulator is forbidden.

So, let's go ahead and do it anyway!



access hole(tip of motor shaft and bushing are visible)

Figure 16 Access to the screw that secures the speed regulator disk

Figure 17 The centrifugal weight mechanism atop the motor shaft



(this cross-section from the 1941 Manual does not show the ball bearing right below the disk; ref. Figure 1) Manually turn the shaft until the screw that secures the collar of the regulator disk to the rotor

shaft, is aligned with the access hole in the side of the motor housing. Remove the screw (M3 x 10 mm).

o The screw will drop to bottom of the speed regulator section of the housing; it is easily retrieved once the speed regulator disk is removed.

Carefully pull the speed regulator disk off the rotor shaft. o The fit between the bore of the disk and the shaft may be tight! In this case, the

disk may have to be "persuaded" off the shaft with a screwdriver. Carefully insert a "thin but wide-blade" screwdriver into the access hole, and slide it between the collar of the flange and the bottom of the compartment of the Motor-Generator housing in which the speed regulator is located. See Figure 17 above. Carefully pry up the flange collar (alternating between both sides of the shaft) until the disk can be removed by hand. I had to do this in my machine, as the securing screw had disappeared, the collar had moved down on the shaft, and the fit was very tight.

10

Put the regulator, the screw and the lock washer in small bag nr. 6.

Figure 18 Centrifugal regulator side views

recessed hole for the screw



Figure 19 Centrifugal regulator top and bottom view The centrifugal speed regulator weighs about 150-160 grams (5 oz.) Once the centrifugal regulator is removed, the top of the motor ball bearing is visible. It is covered with a bearing shield washer. Note that original bearings are "open" type, i.e., they do not have an integrated shield. An external shield was added on top of and below the bearing, to retain the bearing grease. The bearings in my machine had already been replaced with shielded bearings. So there was no greasy mess. In a machine with original open bearings, there probably will be grease or at least the soap part of the grease, that may have turned into a hard cake.

Figure 20 Top of motor housing regulator removed, bearing shield visible (electrolytic capacitor on the right is a replacement from an other overhaul; original was not left in place)

Removing the bearing shield is trivial.

Remove the three M3 x 12 mm screws that retain the cover shield. Remove the shield (34 mm OD, 12 mm ID, 1.7 mm thick). Pull the bushing off the shaft (10 mm OD, 8 mm ID, 3 mm high). Remove the wavy spring washer (21 mm OD, 16 mm ID, 0.3 mm thick). Put the shield, screws (with their washers), the bushing, wavy spring and the speed regulator in

separate bag nr. 7.



A wavy-spring washer (or "wave washer") is a thrust washer that is typically used in high-speed applications, to pre-load a bearing axially. It has an undulating form. It is applied from the outside against the outer race of one bearing, whereas the bearing at the opposite end of the shaft is typically clamped. The shaft, pressing against the inner race, supplies the reactive force. This pre-loading reduces bearing noise and high-frequency vibration. I dont know whether the original bearings were of the deep-groove (Conrad) type.

Figure 21 The motor bearing shield, with bushing and wavy spring washer

the ball bearing, rotor shaft and bushing

Figure 22 Top of motor housing ball bearing shield removed



Note that the cover shield on top of the ball bearing has a matching shield at the bottom of the ball bearing. The screws that retain the top shield are actually threaded into the bottom shield. This bottom shield drops about 1 cm () when the screws are removed, and then rests on the motor commutator. The screws are too short for being screwed back into the bottom shield and pull it back up. A little trick will have to be used to do this, when we re-assemble the motor-generator. Also visible are two electrolytic filter capacitors, see Figure 22 above. They correspond to the components designated C62 and C63 in the schematic (ref. 1-3). They are 12 F, 25/30 volt (operating/max), and marked JAHRELYT. This means that they were manufactured by Richard Jahre GmbH of Berlin. These capacitors are actually packaged in a small cardboard tube that measures 40 mm x 12 mm (length x outer diameter; 1" x "). Electrolytic capacitors (of all vintages) are notorious for large tolerances on their values, significant value changes due to ageing, development of leaks, etc. The inner diameter of the tubes is 9.8 mm (") which means that they can easily be re-stuffed with a modern electrolytic capacitor. See Appendix 5. Source: Schneiders Bauhefte Nr. 6 of 1942

Figure 23 JAHRELYT capacitors from Richard Jahre GmbH and 1942 advertising

Task 7 take the motor carbon brush clips off their pin

This step is addressed in line item 130 of the 1941 Manual:

Unscrew the lead-wires from the terminals [Figure 24, 25], take the pull-springs off their pin, and take the carbon brushes off their bearing pin [Figure 26].

The instructions from the manual make it sound easy enough, don't they? Well, unscrewing the terminals actually is easy, as they are readily accessible. However, the tension-springs are hard to get to! One end of each spring is attached to the clip of the carbon brush and is inaccessible. The other end is hooked onto a short pin, protruding downward from a brass L-bracket mounted on the pertinax ring that is installed against the bottom of the flange that has the socket for the motor ball bearing (see Figure 35 and 55). The spring should be unhooked from this pin, but you just can not get to this pin via the (narrow) oblong holes in the motor housing. So, we are not going to follow the manual here!



Figure 24 Lead-wire of the +12 VDC motor carbon brush

Figure 25 Lead-wire of the -12 VDC motor carbon brush

Loosen the terminal screw of the spade connector on the lead-wire of the + carbon brush of the motor, and slide the spade from underneath the screw.

Loosen the terminal screw of the spade connector on the lead-wire of the carbon brush of the motor, and slide the spade from underneath the screw.

The "classical" way to proceed is to take the -shaped part of the carbon brush spring clips off their bearing pin. This will take "some" fiddling, and several tries (be patient!). Some of the wiring interferes with these manipulations. I used two chop-sticks to do this.

Gently pry the clip of the + carbon brush off its bearing pin, and release it into the innards of the motor-housing.

Gently pry the clip of the carbon brush off its bearing pin, and release it into the innards of the motor-housing.

I think you should SUFFER through this at least once, like I did myself! If suffering is not one of your favorite pastimes, I'm happy to inform you that I found an easier way!

Temporarily skip forward to Task 13, read all the details, look at the photos, and make the required retainer clips out of paperclips

Push and hold each carbon brush clip away from the motor's commutator (see Figure 26 and 27). I use a chop stick to do this.



o Contrary to the "classical" method, the carbon brush clips will not (yet) come off their bearing pin!

install the retainer clips and tie them off with twisty-ties (ref. Task 13).

push here

yellow capacitor

bearing pin

Figure 26 Access to one of the motor carbon brush clips

push here

Figure 27 The motor carbon brush clips and springs The actual carbon brush is permanently fixed to end of a 6 mm (") wide spring metal strip (possibly phosphor-bronze; looks like a copper alloy). The end of this spring has an -shape, beyond which the spring continues almost at a 90 angle. The clip spans 39 mm (1"). The -part of the spring strip is simply clipped onto a bearing pin, with very little force, if any. A cylindrical tension spring pulls the carbon brush against the commutator of the motor, and keeps the clip on the bearing pin.



When we separate the motor housing parts, we have to be very careful not to catch anything on the carbon brushes and damage them! Likewise, during re-assembly.

Task 8 take apart the Motor-Generator housing and remove the rotor The housing of the Motor-Generator shall only be taken apart upon completion of tasks 1-7! The housing of the Motor-Generator consists of three parts, see Figure 1 and 30. They are made of cast iron. From top to bottom: two cylindrical sections, and a tapered part with the base flange. These three sections are held together with two long thin rods: 4.8 mm diameter ( 163 "), and 12 cm in length (4"); the last 15 mm (") at both ends are threaded. The top end of each rod is screwed from below through the separation wall between the speed regulator section and the rotor section of the housing, into the hexagonal stand-off studs of the centrifugal speed regulator. Note that the construction is slightly different from what the 1941 Manual suggests: contrary to Figure 28 below, there is no nut below each hexagonal spacer (nor is there any need for the nuts to be there). The sections of the Motor-Generator housing are held together firmly by tightening the hexagonal studs onto the rods.

hexagonal stud with guide pin

rod

non-existant nut

hexagonal stud with guide pin

rod

non-existant nut

Figure 28 Top ends of the mounting rods The bottom end of each rod is threaded into the bottom section of the Motor-Generator housing, and is visible in a small hole, right above each generator carbon brush holder. See Figure 29.



Figure 29 Bottom ends of the mounting rods

top

base

center

speed regulator

Figure 30 Motor-Generator housing with bracket

As part of Task 5, three wires were de-soldered from the contact plate. They are attached to the housing with a clip that is held in place with a screw and a nut. See the upper part of Figure 22 above. Remove the clip, such that the wiring can move freely.

With a soft pencil, make a mark across the seam between the top and center sections of the housing; this will help expedite precise realignment during the re-assembly.

A bracket (8 mm x 8 cm; 31 x 3") secures the three sections together, with an M3 x 6 mm screw in each section of the housing. See Figure 30.

Remove the three screws from the bracket. Put the clip, bracket, screws, washers and nut into a separate small bag.



Figure 31 Motor-Generator housing bracket

The three sections of the housing are also held together by the rods mentioned above. They are tightened down with hexagonal studs in the speed regulator section of the housing.

Pull the cylindrical springs off the guide-pin extension of the hexagonal studs (Figure 32). Remove one of the two hexagonal studs with an appropriately sized (6 mm) open wrench or a

small adjustable wrench.

o 10 do not use pliers they always cause damage! o mark the stud, such that you can put it back in the same location during re-assembly; this

will make it easier to re-install the contact plate, in case one or both studs/guide pins are no longer straight (as is the case in my machine).

Repeat for the second hexagonal stud. Put the springs and the hexagonal studs in a separate small bag.

Figure 32 Hexagonal guide-pin studs and associated springs The overall length of the studs is 44 mm (1), the hexagonal part being 18 mm long and 6 mm wide ("), whereas the round guide pin is 26 mm long. The guide pin has an M3-threaded hole in the top. The hexagonal stud has an M4-threaded hole in bottom. The upper sections of motor housing will now be loose.

Stand the Motor-Generator on its base.

10 Grab hold of the top section with both hands (base of the Motor-Generator facing away from you) and carefully wiggle it, while pushing down with both thumbs on the outer ring of the motor ball bearing. In my case, the ball bearing slid out of its socket quite easily it is a slip-fit, as opposed to the press-fit installation of the ball bearings onto the rotor shaft.



10 Separate the top two sections of the housing only slightly (1 cm, "). You will feel resistance. Do not force things; also, the wiring may interfere. Carefully proceed with the separation, and feel where and when you need to carefully push some wiring out of the way. The carbon brush springs will probably come of their pins by themselves during this manipulation (unless you did the trick with the paperclips in Task 7).

Figure 33 Motor-Generator housing separated, rotor removed

In my case, the center and base section of the housing did not separate by themselves. I did not try to separate them either, as there is no need for this, even if you want to access the capacitors in the very bottom of the base.

10 Do not pull the rotor out of its socket at the bottom of the housing! While holding the top and center/bottom section, carefully lay the Motor-Generator on its side.



The generator ball bearing at the base of the housing is slip-fitted into its socket. Grab hold of the base of the housing (top of the Motor-Generator facing away from you) and push on the outer ring of the ball bearing with both thumbs, to slide the bearing out of its socket.

Figure 34 Rotor of the Motor-Generator with ball bearings and shields (L: motor commutator, R: generator commutator)

filter capacitor

filter inductor

filter capacitor

filter inductor

carbon brush bearing pin

carbon brush bearing pin

(underneath the wires!)

carbon brush spring pin

carbon brush spring pin

pertinax (?) plate

motor turn direction

Figure 35 Filter components and carbon brush attachment points



The yellow filter capacitors in Figure 35 are 200 pF, 10%, 1500 V manufactured by HOGES (Hochohm Gesellschaft mbH of Berlin). They correspond to capacitors C70 and C71 in the schematic, and measure measures 21 mm x 8 mm (length x outer diameter). The filter inductors are D74 and D75 in the schematic. The schematic does not list their value.

filter capacitor C65

+165 V generator carbon brush holder

-165 V (return) carbon brush holder

filter capacitor C64

capacitor retainer clip

capacitor retainer clip

Figure 36 Looking down into the base of the generator (front side of the housing is towards the bottom of the photo)

As you can clearly see in Figures 33, 35 and 36, there is a grimy black deposit everywhere inside the housing. This is not powdery dust that can be brushed off! Some of it is in the form of small hard black drops, like carbonated grease you might find baked on the inside of the window of an oven or barbeque. I presume it is fried old bearing grease (the original bearings were open type, with additional shields that were not very tight around the rotor shaft) and other lubricants, possibly with carbon brush dust mixed in.

10 Do not use solvents or alcohol to remove the black crud. The crud does not interfere with proper operation of the Motor-Generator. The only cleaning that I did, was use a toothbrush to brush off any loose crud and dust deposits, and then vacuum out the inside of the housing. Appendix 6 discusses some general aspects of cleaning.



Planning the next steps At this point in the process, we have disassembled the Motor-Generator as far as we need to.

Figure 37 The disassembled items

Now it is time to do some refurbishments, before putting it all back together again. We need to: Assess the surface of the carbon brushes and commutators. Remove and replace the ball bearings. Refurbish the paper and electrolytic capacitors.

After having done all that, the remaining re-assembly is basically done in reverse order of the dis-assembly, with some minor twist here and there



Task 9 assess the surface of the carbon brushes and commutators Now we can inspect the carbon brushes of the motor and the generator. Line item 102 and 103 in the 1941 Manual says:

The carbon brushes of the motor must be replaced if they are worn down to a length less than 5 mm [1/5"]. The carbon brushes of the generator must be replaced if they are worn down to a length less than 6 mm ["].

The motor brushes in my machine have about 11 mm length left, and the generator brushes about 9 mm. The 1941 Manual does not mention the length of factory-new brushes. The motor and the generator have a commutator diameter of 24 mm and 27 mm respectively (1). At 3600 rpm nominal rotational speed, this translates to a linear (peripheral) speed of about 4 m/s and 5 m/s respectively. Close to 110 miles per hour! There is an empirical formula (ref. 9) for estimating normal brush wear in mm/1000 hrs:

where D is the diameter of the commutator in mm. Using our commutator dimensions and speed, we arrive at an estimate of a little under 1 mm / 1000 hrs. I have no way of ascertaining whether the formula applies to the carbon brush materials, brush (spring) loading, and electrical loading used in the Feld-Hell machines. The motor brushes in my machine have about 11 mm length left, and the generator brushes about 9 mm. That is, about 3 and 5 mm more that the allowed minimum. So I should have a couple of thousand hours left on the brushes. That is equivalent to about 300-500 standard rolls of paper tape. The 1941 Manual does not mention the length of factory-new brushes. Typically the carbon brushes will not need replacement. Arthur Bauer, PAAOB, has used one of his Feld-Hell machines on a weekly basis for over thirty years, without wearing down the carbon brushes enough to have to replace them. Thirty years at one hour a week is "only" about 1600 hrs

Figure 38 Sliding face of the generator carbon brushes

6.4 mm

5 mm



6.4 mm

6.4 mm

Figure 39 Sliding face of the motor carbon brushes

Figures 38 and 39 above show the sliding face surface of carbon brushes in my machine. The generator carbons appear to have a higher copper content than the motor carbons. I compared these photos against the diagnostic pictures in Appendix 1. This leads me to believe that all carbon brushes are in decent enough shape. I don't have spares anyway!

Inspect the patina and wear-pattern of the generator carbon brushes against the diagnostic listing in Appendix 1.

Inspect the patina and wear-pattern of the motor carbon brushes. Next we'll inspect the appearance of the commutators. Figures 40 and 41 below show the surface of the commutators in my machine. The motor commutator has 24 copper segments (bars), the generator commutator has 36. Commutator bars should appear copper colored with some areas with darker patina ("skin") where the brush contacts the commutator's surface. The patina depends on many factors, such as the environment (dust, lubricant vapors, etc.), electrical field and current, carbon brush material, carbon brush spring loading, rotational speed, etc. I compared these photos against the diagnostic pictures in Appendix 2. This leads me to believe that the commutators are in decent enough shape; yes, there is some streaking, but is hasn't developed into metal transfer or threading.

Inspect the patina and wear-pattern of the motor commutator surface against the diagnostic listing in Appendix 2.

Inspect the patina and wear-pattern of the generator commutator.

As the brushes have to make electrical contact with the commutators, the surface of the commutators should obviously be clean. But do not confuse "dirty" or "fouled" with a perfectly normal patina!



10 mm

24 mm

Figure 40 Commutator of the Motor

11 mm

27 mm

Figure 41 Commutator of the Generator

Line item 99 in the 1941 Manual says:

If the commutators are only lightly fouled, then they are to be cleaned with a cloth that is lightly dampened with kerosene [UK: paraffine oil]. If they are heavily fouled, then the converter motor-generator must be removed in accordance with line item 119, and made to run by applying 12 Vdc. The commutators must be very carefully rubbed down with very fine sandpaper, and then the remains of this sanding and other dirt must be thoroughly cleaned off with a cloth that is lightly dampened with kerosene.



10 Contrary to what the above line item from the Manual may suggest: never make the motor run by simply applying 12 Vdc to it! There will be no motor speed regulation, and the motor speed will run away to about 10000 rpm! Only turn the motor on via the Hellschreibers Amplifier & Interconnect Unit! Note that the above line item from the 1941 Manual implies that the Motor-Generator is completely put together, and the sanding is done by sticking some kind of sand paper or emery-cloth covered appliance (like a lollipop stick) into the spinning machine, through holes in the housing. Better wear safety goggles, protective gloves, etc!

10 Also note that applying any type of abrasive against the spinning commutator even when "only" at the nominal 3600 rpm can do permanent damage to the commutator surface in a very short time. If you really insist on doing this, make sure to only apply very little force and minimal abrasiveness!

10 Never use steel wool to clean the commutators, not even (or maybe especially not) extremely fine steel wool (e.g., type 0000). It doesn't necessarily damage the commutator, but it is impossible to avoid tiny (conductive!) particles of the wool from settling between the commutator bars (and elsewhere!) and it is basically impossible to clean it all off. A fairly safe way of cleaning commutators is with an old-fashioned pink eraser for typewriters or ink. Yes, the rubbings will get in between the commutator bars, but they are soft and non-conductive and the can be removed with a toothbrush or a good whiff of compressed air (e.g., from an air "spray" can).

Task 10 remove the motor and generator ball bearings

Before dismounting the rotor ball bearings and installing replacement bearings, read Appendix 4. The top (motor) bearing in my machine made some noise when spun by hand, like it was running a little dry. There were no noticeable hard points, but still a good candidate for replacement. The bottom bearing made much less, if any, noise. As the machine is disassembled anyway, both bearing will be replaced. For a listing of possible bearing noises, see Appendix 4. The markings on the outer race of the ball bearings that were installed in my Feld-Hell machine indicate that these (replacement) bearings are of type NTN 627 Z and NSK 627 Z. That is:

Manufacturer: NTN and NSK (both good Japanese brands) 627: universal bearing number code.

o Type code "6" means "deep groove" o Diameter series "2" means 22 mm Outer Diameter (OD) o Nominal bore diameter "7" means 7 mm Inner Diameter (ID; "bore", shaft diameter) o Height = 7 mm

shield/seal code: "Z" means " steel shields". Note that other manufacturers use ZZ or 2Z for this type, and use Z for bearings that are shielded on one side only.

Per the NTN catalog, the NTN bearing has a limiting speed of 32,000 rpm (other manufacturers have different speeds for their 627s). The Feld-Hell runs at 3600 rpm: the low end of what is considered "high speed". The weight of this bearing is 13 grams ( oz.). Line item 144 of the 1941 Manual says:

The ball bearings of the Motor-Generator shall not be replaced. Well, at least not as part of field maintenance! In addition, line item 100 of the 1941 Manual says:



Every 100 operating hours, but at least every 8 weeks, the Feldfernschreiber must be oiled and greased in accordance with line items 135 through 142.

Note that this includes the ball bearings of the gear-box and the character drum. Most of these bearings turn at a (much) lower speed than the Motor-Generator bearings, so the latter bearings need even more attention! Furthermore, as stated in ref. 3:

Grease should not be allowed to remain in a bearing for more than 48 months, or if service is very light and temperatures low, 60 months, irrespective of the number of hours' operation during that period, as separation of the oil from the soap and oxidation continue whether the bearing is in operation or not.

So, even if the original bearings have at some point been replaced with "greased for life" shielded bearings, and still appear to be OK at this time (based on their noise and feel) it may be time to replace them! As can be seen in Figure 44 below, both ends of the rotor shaft have a collar ("shoulder") close to the commutator, against which the ball bearings are installed. So it is not necessary to measure how far down the shaft the bearings have been seated, to be able to mount the new bearings in the same position. Anyway, I did measure how far the rotor shaft sticks out beyond the bearings in my machine: 17.02 mm (probably 17.0 mm nominal) and 10.14 mm (probably 10.0 mm nominal) respectively for the motor and the generator bearing. Clearly, the distance between the two collars is the critical dimension: 129.0 mm.

Figure 42 Rotor of the Motor-Generator and bearing shields bearings removed (L: motor commutator, R: generator commutator)

There are two standard methods to remove ("dismount") a ball bearing from a shaft: pull the bearing off the shaft with a bearing puller (surprise!), or push the shaft out of the bearing with an arbor press. In the end, the relative movement is the same. A bearing puller looks like a scissor device with two or three "legs" or "claws, and has a "forcing screw" ("jack screw") piston at the center. See Figure 43. The one-legged types don't work very well . The tips of the claws are placed behind the bearing that is to be removed, and the forcing screw (jack screw) is applied to the tip of the shaft. The screw is then turned, thereby pushing the shaft out of the bearing (or, conversely, pulling the bearing off the shaft). Ideally, the claws should pull on the bearing's inner ring. Often, the "fingers" of the claws will not reach the inner ring, in which case the bearing is pulled off by the outer ring. This is OK if the bearing will be replaced anyway. Note that there also exist so-called "blind" bearing pullers. Their thin, narrow claws pass between the balls of the bearing and pull on the inner ring. They tend to be rather expensive!



Figure 43 Bearing pullers and a bearing splitter

As you can see in Figure 44 below, there is not much room between the bearing and the commutator. There is even less room between the original bearing shield washer (installed between the bearing and the commutator) and the bearing. The claws of a standard bearing puller will not fit. The options then are to apply the puller to the bearing shield washer, or use another tool. The washer is made of soft metal, and will probably just fold around the bearing when pulled. In this case, an excellent method is to use a two-legged puller in combination with a so-called "bearing splitter" (a.k.a. "bearing splitter plate", "bearing separator", "strong back puller"). See Figure 43. This puller attachment is specifically designed for insertion behind bearings, where space limitations preclude the use of a standard jaw puller. The other option is to use an arbor press. In this case, the bearing must be fixed in place with some sort of jig such as a bearing splitter, mounted in a bench vise.

original bearing shield

bearing

Figure 44 Limited space for bearing puller between bearings and commutators

10 Prevent bulging and swelling of the tip of the shaft (so-called "mushrooming"). Put a small soft metal disk (e.g., 1-2 mm thick brass, copper, aluminium softer than steel) between the tip of the shaft, and the tip of the center of the tip of the jack screw of the bearing puller (or of the arbor quill). Note that the rotor shaft is made of relatively soft steel. Both ends have a dimple or shallow drill hole from when the shaft was machined and the commutators were trued on a lathe. If in your machine this hole is threaded, then put a short flathead screw in it, and use the screw head as the point where to apply pressure with the puller or press.



10 Prevent seating damage! Make sure that the center of the tip of the jack screw of the bearing puller (or of the arbor quill) acts on the center of the shaft. If you have a choice, use a self-centering puller.

10 Note that even small bearing pullers are capable of applying considerable forces! Do not misuse the tool by just continuing to tighten the puller screw more and more, if the bearing doesn't move. Eventually something will give, and be damaged. I do not (yet) own a puller and splitter, and could not find a local store that carries them. Note that some on-line tool suppliers sell bearing puller/separator sets that are reasonably priced (but are probably not meant for professional or industrial use). After some searching, I found a small local company that re-winds and repairs electric motors and generators, small and large. This 3-man shop enjoys a nationwide (positive) reputation, so I was confident that they know what they're doing. In addition to showing me around and explaining their projects, they were nice enough to carefully pull the bearings of my rotor with the aid of a bearing puller (OK, and some simple "helper" tools of the trade). Free of charge! They assured me that the tightness of the fit of the bearings on the rotor shaft was normal/OK.

Task 11 mount new ball bearings Bearings of brands such as SKF, NSK, Fafnir, BSB, and NTN are "known-good" (note that this is not an exhaustive list). Nachi is considered sub-top. Bearings made in China (independent of whether the brand name is Chinese!) may have to be treated with some suspicion. Good ball bearings are not overly expensive (early-2009 list price for a good "627" bearing is about $5-10 in the US, 3-8 in Europe). Saving a little money by choosing lower quality parts is a bad idea, especially when going through the substantial trouble of disassembling the motor-generator. Note that type 627 (7 mm bore) and 608 bearings (8 mm bore) are standard for skate boards and in-line skates, so your nearest skate board shop may carry what you need, and at a reasonable price level. Hang loose !

Figure 45 My new ball bearings in standard packaging Before mounting the new ball bearings onto the rotor shaft, we have to decide whether to re-install the original shield washers. If we install pre-greased shielded ball bearings (recommended) then it is actually not necessary to put them back in, at least not because we need them as grease shields. However, these



shields also limit the axial movement of the bearings and, thereby, of the rotor. The bearings are mounted into the housing with only a slip fit a fit that is much less tight than the press fit of the bearings onto the rotor shaft. So it is probably a good idea to reinstall them, even though it is a hassle to do so! If you decide not to install them, then at least install the washer below the generator's bearing before putting the rotor back into the base of the housing. See Task 15. Before we do anything, here are some general rules for dealing with new ball bearing:

Never use replacement bearings of unknown origin and/or history (e.g., from your junk box). Never drop bearings. Never squeeze a bearing in a vise (unless for the purpose of destroying it). Never press fit a bearing onto a shaft by applying force across the bearing raceways, through the

bearing balls. This will always destroy the bearing due to permanent brinelling damage to the bearing races. The most common cause of failure of small ball bearings is excessive force applied during assembly!

Also:

10press only the inner ring, to press fit the bearing on the shaft. 10apply force evenly along the ring. 10when you start pressing or tapping, make absolutely sure that the bearing is getting seated

straight onto the shaft, otherwise you will ruin the shaft, the bearing, or both!

10 press only the outer ring, to press fit a bearing into the housing socket.

There are two basic ways to mount a bearing onto a shaft: Mechanical force - press a bearing onto the shaft. Differential thermal expansion - reduce the diameter of the shaft by cooling the shaft, and/or heat the

inner ring of the bearing to increase its bore diameter. When press fitting, you need two things: a press and a drift. Bearings must be pushed straight onto the shaft: the centerlines of the bearing and the shaft must be aligned (i.e., coincide coaxially). A drift is used to ensure that the pressing force is only applied to the inner bearing ring, and is applied evenly around the ring. Pressing is normally done with an arbor press.



Figure 46 A small arbor press and the cross-section of a drift A drift is a hollow, straight-edged cylinder with an inner diameter just slightly larger than the diameter of the shaft. The drift pushes down on the inner ring of the new bearing, and thereby that inner ring onto the shaft. You can buy "official" drifts, but I happened to have a couple of old open and shielded 608 bearings in my junk box. They have a bore of 8 mm, which makes their inner rings perfect drifts for the inner ring of 627 bearings (7 mm bore). Simply punch a hole in the shield with a nail and hammer, pop the shield off, drill through the ball retainer, pull out the retainer with needle-nose pliers, move the balls up against each other, and pull the inner ring out with small pliers. So, don't throw away old bearings, they may come in handy!

Figure 47 Rings of discarded bearings can be used as drifts If you don't have access to an arbor press, you can use a drill press and a decent drill press vise. This actually works very well, and is what I did (see Figure 48), after I applied the thermal method described below to get the bearings started onto the shaft. Note that you don't need an industrial-size drill press. As an absolute last resort, you may try and carefully tap the drift with soft-blow mallet or plastic-tip hammer, or a regular hammer and small block of wood. Support the opposite end of the shaft a flat hardwood block, on the floor or a solid work surface. But this is bad practice



Figure 48 Using a drill press, vise, and bearing ring drifts "Hot mounting" is typically only used for large open-type bearings with an outer diameter of over 5 cm (2"). We can get also get the required temperature difference by cooling the rotor shaft. A temperature difference between bearings and shaft of 80-90 C (145- 165 F) should suffice. I have tried applying generous amount of ice spray to the shaft ends to accomplish this, without the desired result. I then used the following method to at least get the bearings properly started onto the shaft:

Clean the rotor shaft ends with a clean, lint-free cloth Re-install the bearing shield washers onto the shaft ends (you can see from their markings which

side should face the commutator and which side the bearing) Pull the shield washers up against the commutators, and hold them there by threading strings or

rubber bands from each of the three holes in one washer to the holes in the opposite washer o we will not have the time to get the washers out of the way when we are going to seat the

bearings! Put the rotor and the bearing shield washers in a Ziploc freezer bag, suck the air (and moisture)

out, and put the bag into the freezer overnight at -32 C (-25 F). Remove the bearings from their package with clean dry hands

10 New bearings are very lightly coated with rust inhibiting grease or oil. Do not remove this coating!

Before taking the bag with the rotor out of the freeze, put the bearings in another Ziploc freezer bag (use a couple of layers of good kitchen food wrap film if you don't have such bags), suck the air out, stick it in a pot, and add boiling hot water.

o Do not get the bearings wet! o My new bearings are made by SKF; the grease used in SKF bearings can be warmed up to

100 C (212 F) operating temp without a problem. Version 1.1, 23 May 2009 43 2009 Frank M.G. Drenberg, N4SPP

Restrictions stated on the cover page apply. www.nonstopsystems.com/hell.htm


The next steps must be done very quickly!

Take the bag out of the freezer and the rotor and shield washers out of the bag (avoid warming up

the rotor shaft ends by touching them) put the bearing washer on to each shaft end (correct side towards the commutator) quickly slip on the hot new bearings

o 10 stop trying to push the bearing onto the shaft as soon as you feel resistance and the inner ring seizes on the shaft. This will only be a fraction of a second!!!

remove the strings between the bearing shields. This way, I was only able to just slide the bearings onto the shaft ends, i.e., no shaft sticking out beyond the bearings. The shaft and the bearings are so small that they do not have enough thermal mass to retain the temperature difference long enough to completely mount the bearings. If you have access to a standard "electronics industry" temperature test chamber that can go down to -50 C, you may be able to do the entire mounting process without a press (not having done this, I cannot guarantee that this works any better then a domestic freezer). After getting both bearings started this way, I simply pressed them all the way to their respective shaft-collar with the aid of a drill press and several 8 mm inner bearing rings for drifts. See Figure 48 above. Task 12 refurbish the capacitors At this point we still have access to all the filter capacitors of the Motor-Generator. From bottom to top:

0.25 F, 250/750 Vdc - paper capacitor between each generator carbon brush and ground (ref. Fig. 36)

200 pF, 1500 Vd (yellow) ceramic filter capacitors above the (ref. Fig. 35) 12 F 25/30 Vdc - electrolytic capacitors just below the centrifugal speed regulator disk (ref. Fig. 20) 2000 pF, 500/1500 Vdc - paper capacitor on the contact plate of the speed regulator (ref. Fig. 13-15) 500 pF, 500/1500 Vdc - paper capacitor on the contact plate of the speed regulator (ref. Fig. 13-15)

In addition, there are two more electrolytic caps on the outside of the Motor-Generator (ref. Figure 53):

10 F, 25/30 Vdc - electrolytic capacitors from the +12 Vdc and the 12 Vdc return, to ground. Clearly, these last two capacitors remain easily accessible after the Motor-Generator has been reassembled, but we might as well take care of all the capacitors now. Appendix 5 provides details regarding the options of replacing, rebuilding (re-stuffing), and reforming of old capacitors. I personally prefer and recommend rebuilding these electrolytic and paper capacitors into their original tubular package. The ceramic capacitors should only be touched if they are physically broken. The two brown generator filter capacitors that are (barely) visible in Figure 36 above, correspond to C64 and C65 in the schematic (see Figure 49 below). They are manufactured by Siemens-Halske and are marked 0.25 F, 750/1500 Vdc (Betrieb./Spitz. = Operating/Max), 70 C (160 F). They are paper capacitors, packaged in a cardboard tube that measures 37 mm in length and has a 16 mm outer diameter ( 1" x ").

Version 1.1, 23 May 2009 44 2009 Frank M.G. Drenberg, N4SPP

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Feld Hell Motor Generator Overhaul