Four Facet Drill Grinding Jig

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Four Facet Drill Grinding Jig - Construction Notes

This drill grinding jig is based on a design published in Model Engineer magazine in the mid-1990s. I do not have a copy of the magazine, but I made some notes from the original article.

I made a number of changes to the design as originally published to make the jig easier to useon my grinder. The notes below, and the associated drawings, are compiled from my sketchesin my notebook and measurements taken from the jig I made.

Throughout these notes reference is made to brazed construction. I MIG welded my unittogether, each joint held by a few tack welds rather than a complete unbroken bead on theseam. It doesn’t look as pretty, but it works just as well.

No dimensions are critical except those that determine the grinding angles, and the cross holesin the four guide blocks (parts 20) which take the drill to be sharpened – these holes must beon the centreline of the blocks, or the symmetry of the drill point will suffer.

When matching the jig to a particular grinder it may be necessary to change the height of theMain Body (part 6) to ensure the drill point is at approximately the same height as thegrinding wheel centre. Similarly, the ‘reach’ of the body (dimensioned as 35mm on the

drawing) was necessary to clear the base of my bench grinder – this may need to be changedto match the grinder that the jig is being fitted to.

All sheet metal parts are made from 2mm thick material. Again, this dimension is not critical,but if changed, the appropriate changes may be made to the relevant dimensions on parts 4,10 etc. for cosmetic reasons.

For most parts the materials are not critical – I recall that in the original article the drillsupport was made of aluminium and the various knurled screws were made of brass.

Two alternative constructions are shown for the drill end-stop. The original article describeda component fabricated from sheet (parts 13-16). I made the stop from a solid block (part 22)

secured by a screw (part 23).

The M3 x 0.5 threaded hole in the feed stop bush (part 8) was intended to take a grub screwand a nylon or copper pad to act on the feed stop (part 9) to prevent it changing setting dueto vibration. I cut the M6 x 1 thread on the feed stop with a split die adjusted to cut thethread a little large so it is a firm fit in the bush – further anti-vibration precautions proved to

be unnecessary and the grub screw and pad were never fitted.

The pivot stud hole in parts 1, 2 and 3 is initially drilled 2mm.

After the parts are brazed together with the pilot holes aligned, the hole through all three partsis opened out to 3.3mm and tapped M4 x 0.7

When the pivot stud hole has been tapped, a short length of M4 studding (a bolt with the headcut off) is brazed into the tapped hole – the spelter being fed in from the part 1 side to prevent

it flowing into the thread that will take the nut/locknut.

Four guide blocks (parts 20) are specified, each with a different size cross hole. The crosshole takes the drill to be sharpened and each block covers a range of 1mm in diameter (e.g.the 3mm hole covers drills from 2-3mm dia. Etc.). Although four guide block screws (parts21) are specified, only one is needed in reality as the same screw can be fitted to which everblock is in use.

Ian Newman

[email protected]



Four Facet Drill Grinding Jig – Instruction For Use

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Installation

The 8mm bar that forms the top of the base body must be at 90 degrees to the grinding wheel

surface.

Position the base body so that when the feed stop is fully unscrewed the main body is just clear of

the grinding wheel surface. Check this in both the 10 degree grinding position and the 30 degreeposition.

Check the location of the jig. Read the section on Using The Jig (below) and put a few drills of

various sizes in the machine to check that there is enough movement to allow the unit to operate– if you use a bench grinder you will find things are a bit tight under and around the grindingwheel and some wood blocks will probably be needed to bring everything to the right height.

Secure the jig to the bench.

Using the Jig

1) Using the smallest guide block that will fit the drill, place a guide block on the drill body atthe base of the flutes.

2) Looking onto the point of the drill, rotate the drill until the line of the cutting edges (the lips)

are at 90 degrees to the long axis of the guide block – see diagram below.

For small drills a loupe or other magnifier is a help here. As the drill is ground back, the lineof the lips rotates in a clockwise direction (down the helix of the flutes) so this position may

need to be reset if you are grinding back a particularly blunt drill.



Four Facet Drill Grinding Jig – Instruction For Use

Page 2

3) Set the grinding jig in the 30 degree position (with the angle setting lock screw located inthe lower locking guide). Place the rocker vee at the bottom of the main body over the

rocker bar that forms the top of the base body and adjust the feed stop so the jig is 2-3mm

clear of the grinding wheel surface.

4) Place the drill in the drill support groove and adjust the drill end-stop until the drill is just

touching the grinding wheel.

5) Press the drill clamp down to hold the drill in place, check that everything is clear of thegrinding wheel then start the grinder.

Holding the drill clamp firmly against the drill and pushing the rocker vee feed stop againstthe end of the rocker bar, rock the drill across the grinding surface (observing all the usual

safety rules)

6) Take the drill off the jig, rotate through 180 degrees and repeat to grind the other edge.

7) Adjust the feed stop to take off a little more from the drill and repeat steps (5) and (6) untilboth sides of the drill have been ground to a smooth, uniform condition.

8) Stop the wheel and reset the adjustable body to the 10 degree position.

9) Using the feed screw adjust the position of the drill so it just touches the grinding wheel

surface.

10) Start the grinder and repeat the grinding process to produce a thin 10 degree lip on each

side of the drill.



Four Facet Drill Grinding Jig – Parts List

Item Description Material Dimensions Qty1 ADJUSTABLE BODY MS 1

2 ANGLE SETTING PLATE MS 1

3 PIVOT BLOCK MS 14 ANGLE SETTING LOCK BUSH MS 1

5 ANGLE SETTING LOCK MS 1

6 MAIN BODY MS 1

7 ROCKER MS 1

8 FEED STOP BUSH MS 1

9 FEED STOP MS 1

10 ANGLE SETTING LOCK GUIDE MS 2

11 DRILL SUPPORT MS 1

12 DRILL CLAMP Nylon 1

13 DRILL END-STOP PLATE MS 1

14 DRILL END-STOP PLATE GUIDE MS 2

15 DRILL END-STOP LOCK MS 116 DRILL END-STOP LOCK NUT MS 1

17 BASE BODY MS 1

18 ROCKER BAR Silver Steel 1

19

20 GUIDE BLOCK MS 4

21 GUIDE BLOCK SCREW MS 4

22 DRILL END-STOP BLOCK MS 1

23 DRILL END-STOP LOCK SCREW MS 1

24

25 PIVOT STUD MS M4 x 0.7 x 15 1

26 PIVOT WASHER MS M4 crinkle 1

27 PIVOT NUT MS M4 x 0.7 1

28 PIVOT LOCKNUT MS M4 x 0.7 1

29 FEED STOP FRICTION PAD Nylon 1

30 FEED STOP FRICTION SCREW MS M3 x 0.5 grub 1

31 DRILL SUPPORT SCREW MS M3 x 0.5 x 5 hex 2

32 DRILL CLAMP SCREW ∅3 x 12 self tap 2

33

34

35



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Four Facet Drill Grinding Jig