TM 9-1595 ( Ordnance Maintenance Prismatic Compass, M1918 ).pdf

7/22/2019 TM 9-1595 ( Ordnance Maintenance Prismatic Compass, M1918 ).pdf

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TM 9-1595

W A R D E P A R T M ENT

TECHNICA L MAN U AL

O R D NA NC E M A I NT EN A N C EPRIS MA TIC COM PASS, M 1918

uly 17, 1941


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TM 9-1595. . . W A R .DEPARTMENTECHNICAL MANUALNo. 9-1595

ORDNANCE MAINTENANCEPRISMATIC COMPASS M 1918

Prepared under direction of theC hief of rdnance

S E C T I O N I. General. Paragraph ^ DPurpose________________________ 1 -Scope__________________ 2References__________________ 3 ^7II. Descrip tion.Description _______________ ^

III. Operation and adjustment ^Operation____________________ 5 ^Field test and adjustment_____________ 6 Q

IV Inspection.Inspection_________________________________ _V . Maintenance and repairDisassembly and assembly____________ 8 Adjustment________________ 9

VI Care and preservation P a eCare and preservation _____________ 10A P P E N D I X List of references_________ __ __________ 12

S E C T I O N I

GENEKAL ParagraphPurpose__________________________________________ 1Scope________________________________..__._________ 2References________________________________________ 3

1 Purpose.This manual is published primarily for the information and guidance of ordnance maintenance personnel.

132589741


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TM 9 1595 '2-4 O R D N2. Sgope.r-This .manual supplements the"technical manuals which

are prepares ifol t-h'e -Wing aifm. t contains descriptive matter, operating instructions, and ' detailed instructions for maintenance andrepair:byorfJll^nce-pefio'rinsL* '.3. Kefe'reirces.Thfe 'appendix lists the publications pertaining tothe prisriiatic. compass. .'*

' S E C T I O N IIDESCEIPTION ParagraphDescription_______________________-_________ _ 4

4. Description. The prismatic compass is a multiple-purposeinstrument for obtaining clinometer, angle of site, and magneticazimuth readings. t may be used with 155-mm howitzers, M1917,M1918 and modifications ; 75-mm guns, M1897, M1897A2, M1917 andmodifications ; 7 5 - m m pack howitzers, Ml and MlAl and with otherfield artillery.

. The instrument contains a compass dial, B137958, and a clinometer dial, C70112. The clinometer dial carries a lead weight,B137954, which causes it to indicate vertical angles when the instrument is held vertically. In order to make the instrument compact,the clinometer dial is mounted just above the compass dial. A portion of the clinometer dial is cut away so that the compass dialbelow may be viewed. The compass dial is colored green, and theclinometer dial is white.

Folding sights are provided at front and rear. The rear sight,B137950, is hinged to the rear sight slide, B137951, and can be raisedor lowered ^to focus the magnifying prism, A49372, on either the,compass dial lor the clinometer dial. The function of the prism isto superimpose .upon the field, as viewed through the sight, the image.-of the clinometer ^P 'compass dial, so that accurate readings may betaken by uaijig the~vaijie of the front sight as it appears on the imageof ihe dial The Sesf sight, assembly, consisting of the leaf sight

s, A4992, and-le@ sight vane holder, B137957, is hinged to thesight bracklt^B137959. When turned down, the leaf sight' f rigages the corilpgii lift bar, A49378, which lifts the compass dial

from its ^vot^-aSd clamps it. The dial remains clamped until theleaf sight is opened for operation.

A compass dial locking plunger, A49386, protrudes through thecase, C70110, near the rear sight, and a similar plunger, A49385,protrudes through the front sight bracket, B137959. When eitherplunger is pressed, it causes a flat spring, A49387, to bear againstthe edge of the compass dial, and acts as a brake for damping.


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T 9 595PRISMATIC COMPASS, M1918 4 5

The clinometer wedge knob, A49374, when fully depressedclamps the linometer dial against rotation, and when partiallydepressed acts as a brake for damping./. The plane supporting surface of the case support, B137952, isparallel to the line of sight passing through the front and rear sights.

The instrument is furnished complete with carrying case fig. 3).Prismatic compass, M1918, and manufacturedby the Sperry Gyroscope Company, is a limited standard item forissue by the Ordnance Department. These compasses aregraduated

in mils and are distinguished from the compasses issued by theEngineer Corps which are graduated in degrees. The tripodpreviously issued with this item is now notauthorized.

S E T IO NOPEEATION AND ADJUSTMENT

ParagraphOperat ion 5Field test and adjustmen t 6

5. Operation. To measure angles of site, raise the leafsightand the rear sight. Pull out the clinometer wedge knob to permitfree rotation of the clinometer dial. Focus the rear sight on thelinometer white) dial, sliding the sight as required. Hold the instrument with the dials in a vertical plane, look through the niche inthe rear sight,and elevate or depress the instrument until the objectobserved is in line with the leaf sight vane. The angle of site, reflected in the rear sight prism, will also be visible in the enter ofthe field of view. The angle of site scale the outer scale on theclinometer dial) is graduatedat 5-mil intervals and numbered at 100-milintervals; the 50-mil points are also marked. A 300-mil indicationcorresponds to a level line of sight, as on the corresponding scales ofrange quadrants. The clinometer wedge knob may be partially depressed to damp out oscillations; it must not be depressed when takingthe reading.6. To measure azimuths, first operate the instrument in angle ofsite until the compass green) dial is exposed at the rear sight bythe cutaway portion of the clinometer white) dial. Depress theclinometer wedge knob. Kaise the leaf sight and the rear sight.Focus the rear sight on the compass green) dial, sliding the sight asrequired. Hold the instrument in the hand or support it on a convenient nonmagnetic body, look through the niche in the rear sight,and rotate the instrument in azimuth until the object observed is inline with the leaf sight vane. The magnetic azimuth, reflected in


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TM 9-15955 7 ORDNAN CE DEPARTMENT

the rear sight prism, will also be visible in the center of the field ofview. The compass dial is graduated at 10-mil intervals and numbered at 100-mil intervals. Additional numbering is provided in the3200-6400-mil half of the scale to correspond to thenumbering on theazimuth scales of panoramic telescope s whichare graduated 0-3200mils in this range. To damp out oscillations of the compass dial,gentlydepress one of the lockingplungers; plungers must notbe inthe depressed position when taking the azimuth reading.To use the instrument as a clinometer pull out the clinometer wedgeknob andstand the instrument on its support, prism to the rear, ona straight portion of the piece which is parallel to thebore. Thereadingof the linometer scale at the etched line on the lower window is the elevation of the piece. The clinometerscale is graduatedat 10-mil intervals and numbered at 100-mil intervals. A 300-milreading indicates the bore of the pie ce to be level. The sights shouldnot be raised when using the instrument as a clinometer. The clinometer wedge knob may be partially depressed to dampout oscillations it must not be depressed when taking the reading.

To prepare the instrument for traveling, push in the clinometerwedge knob clamping the clinometer dial) and turn the leaf sightdown clamping the compass dial). Lower and fold back the rearsight. Place the instrument in the leather case provided.6. Fieldtest andadjustment.Test the alinementof clinometerdial by noting scale readings with instrument on a level referencesurface. Scale should read 300 through lower window and throughmagnifying prism. If scale readingat either point is not correct,note the error and apply necessarycorrection in subsequent use of theinstrument. Corrective adjustment by the usingarm is not permitted.

S E T I O N IVINSPECTION

Paragraphnspection___________________________________________ 7

7 . Inspection.Inspection is for thepurpose of determining thecondition of the instrument, whetherrepairs or adjustments are required,and the remedie snecessary to insure serviceability and properfunctioning. The listing below will serve as a guide for inspection.

General appearance. Note bent or missing partsloose or missing screws and condition of win dow.


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PRISMATIC COMPASS l 9 18T 9 5957

Rearsight assembly.

Frontsight assembly.

Clinometer dial.

Compass dial.

. Try fit of slide and hinge.Parts should operate smoothlywith suff icient friction to remainin position at the operating settings. Motionof slide shouldbesufficien ttopermit obtaining clearfocus positions for compass dialandclinometer dial.

Hinge should operatesmoothly with sufficien t frictiontoholdleafsightinoperatingposition. Vane should be straightand trueinvane holder. Compassdial should lock properly whenleafsight is turneddown.

Operate clinometer wedgeknob tosee thatit locksdial whendepressed and releases dial whenpulledoutward. Turninstrumentwhile holding vertically to seethat dial operates freely throughacomplete revolution. Also he kwith instrument on fixed surfaceby releasingdialfromseveral different initial positions; final indicationfromeach positionshouldbe the same. finaccuracies dueto friction in the dialmovementarenoticed in the above tests instrument requires overhaul.

Operate compass dial lockingplungers to see that theyfunctionproperly. Release dial holdcase level andturnso as to he k freedom ofmovementofcompassdial.Check accuracy of compass readings by comparison with an instrument of known accuracy;readings should be correct withinatoleranceofplusorminus 5 mils.Note time required for compassdial tocome torest; aweak magnetic needle is indicated if dial


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TM 9 15957 8 ORDNANCE DEPARTMENT

takes more than 4 seconds to return to equilibrium position afterswinging beyond it.

Alinement . /. When the compass is leveled,with sights in using position, therear sight notch and leaf sightvane should be vertical as determined by sighting on a plumb l ine.Scale readings on clinometer dialshould 'be the s ame when readthrough magnifying prism andthrough lower window opening.Index line in lower window opening should be perpendicular tobearing surface of case support.

S E C T I O N VMAINTENANCE AND EEPAIE

ParagraphDisassembly and assembly_______________________________ 8Adjustment _________________________________________ 9

8. Disassembly and assembly.Disassembling of the instrument is required only for repair purposes and for the performance ofcertain adjustments. Comple te stripping is not normally required.

The rear sight, assembly, and front sight, assembly, are readilyaccessible for replacement of componen t parts. The straight pins onwhich the sights hinge are riveted lightly at each end.

. The case, assembly, can be opened by removing the two ovalhead screws, A49391A, which secure the cover, C70111, to the lowercase, C70110. (See fig. 2, sec. D-D-D-D.) The three similar screwswhich secure the clinometer dial support, B137955, are not to be removed at this t ime . The case support, B137952, can be removed ifnecessary to permit opening the case, but its position should be markedbefore remova l to insure correct positioning on reassembly. Whenprying off the cover, be careful to prevent damaging the compass dial,which may fall out of the case. When the case is opened, the upperhalf will contain the clinometer m e c h a n i s m and the lower half willcontain the compass mechanism, both of which will be accessible foradjustment or further disassembly.

To replace the glass window, A49380, r emove clinometer dial support, B137955, clinometer dial, assembly, and round nut, A39925.Examine cork pad, A39924, and replace if necessary. hellac outer6


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TM 9-1595PRISMATIC COMPASS, Ml 9 18 8-10

edge of pad to cover and window whe n assem bing. Assemble windowwith chamfered edge toward pad and with index line in center ofclinometer opening. Adjust window to place index line in properposition, as described in paragraph 96 (1).Assembling operations are performed in the reverse order ofdisassembly.9. Adjustment. No specific adjustment is provided for thispurpose. Friction caused by rubbing of the flat spring, A49387,against the compass dial can be removed by bending the spring toprovide clearance. Friction on clinometer dial pivot pin can somet imes be removed by bending clinometer support, B137955. If t h e s emeasures are not successful, replacement of affected parts is required.Comple t e alinement of the clinometer portion ofthe instrument is performed in three steps, as follows:(1) Set index line by turning window, A49380, until clinometerscale reading at index line is s a m e as scale reading through magnifying prism.(2) Using the sights, read angle of site of a reference point ofknown angle of site. If reading obtained is not correct, shift leadweight, B137954, on clinometer dial until correct reading is obtained.(3) Stand the instrument on a level reference surface. Note clinome te r scale reading. If reading is not correct, loosen two fillisterhead screws which secure case support, B137952, and shift case support until correct reading is obtained. Secure case support in thisposition. Spring, A36657, which bears against rear sightslide, B137951, can be adjusted to provide proper degree of friction inoperation of slide. S E C T I O N VI

CAEE AND PKESEEVATIONParagraphCare and preservation_______________________________ 10

10. Care and preservation. The instrument should behandled carefully to avoid unnecessary shocks. t should be kept inthe carrying case when not in use. After use in wet weather, theinstrument should be wiped dry before being placed in the carryingcase.J. When the instrument is moved f rom one position to another, theleaf sight should be turned down to c lamp the compass dial and theclinometer wedge knob pushed in to c lamp the cl inometer dial, therebypreventing injury to the pivots.


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TM 91595OEDNANCE DEPARTMENT

Particular care should e taken to prevent bending of the leafsight vaneor leaf sightvaneholder.

Moistureduetocondensationmaycollect in the instrumentwhenthe temperature of thepartsis lowerthanthat of the surrounding air.Thismoisture ifnot excessive can eremovedby placing the instrument in a warmplace.

lubrication is requiredforthis instrument.


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PRISMATIC COMPASS Ml9 8TM 9 159510

SCREW-A4939IASCREW-A4939IASPRING -A366S7SCREW-BC6X4BT

SECTION C C

COVER-C70III WHDOW-A49380-P1NSTCHT-O36x|j|OIALC70II2NUT A39925

SCREW-BCL X4BC-

OISK A49382PAD A39924SCREW A4939IANUTA4939WEIGHT BI37954

JEWEL A3908HOUSING-A39739

F rumti- : 2. Prism at ic com pass M101Ssocti oned views.


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TM 9 1595ORDNANCE DEPARTMENT

PIN.STGHT ^xfj HOLDER BI37957SIGHT BI37950 VANE A49392

SPACER A4937I PIN.STGHT ^xjiPRISMA49372 BARA49378HOLDER A49390 HUB A 49373

SLIDE BI3795IAOAPTER BI37953J

-SCREW.OVAL HD-.112x1KNOB A49 68CATCH A49 7

LEVER A49370JB R A CKET 6137959

SCREW A39923WASHER A49377

PLUNGERA49 85

PLUNGERA49386GUIDE 6137956SCREWFIL.HD-.ll2xl

SE TIONE E

SPRING A 49387RIVET A49388

ORD 14608U K S 2.Prismatic compass, M1918sectional viewsContinued.

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TM 9 1595 O R D N A N C E DEPARTMENTA P P E N D I X

LIST of EEFEEENCES1. Standard Nomenclature List.

Compass, prismatic, M1918 (Sperry type)_____ SNL F-232. Technical Manuals.Materiel inspection and repair____________ T M 9-1100

[A. G . 062.11 (5-26-41).]BY OKDEK OF THE SECRETARY OF WAR : G . C . MARSHALLOFFICIAL,E. S. ADAMS

D I S T R I B U T I O NB and H (6); E 2,4-7,17 (2); Bn9 (2); 1C 9 (4).(For explanation of symbols, see FM 21-6.)

12. S GOVERNMENT PS'IPTING OFFICE: 1941

For sate by the Superintendent of Documents, Washington, D. C. - - - - Price 5 cents