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Harold Hall

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The instructions for using the jig (very limited) state that the drill should project beyond this by an amount equal to the drill's diameter though I have found it necessary to adjust this value. From here I will describe a method based on the jig's rotational stop not being used for that purpose. It should though be moved away from the drill and just used as a reference point for measuring the drill's projection.

 

First set the drill to project from the stop by an amount nominally equal to the diameter of the drill. This being to the outer end of the cutting edge and not the drill's tip. With that done the end stop should be set so as to maintain the drill's axial position between sharpening sides one and two, Photograph 8. The drill should now be rotated such that the cutting edge is vertical so that the whole length of the cutting edge arrives at the grinding wheel at the same time as the jig is rotated. A substantial error in this setting will cause the drill to be sharpened with a domed end as Sk. 6 illustrates. Like the 130° angle, this requirement is not vital, a few degrees error will have  limited effect. Actually, more important than the tendency for the drill to be domed will be that the chisel angle will be moved around by an amount equal to the error in the angle set.

 

Above I mentioned my reservations regarding the rotational stop, the reason being that at the required projection it did not if used result in the cutting edge being vertical.

 

To recap then, we have set the drill's projection and the cutting edge vertical and are ready for the next stage. Photograph 9 shows that the jig has a slotted base for mounting it onto the off hand grinder's base board that can now be used to bring the drill's tip to a position that it is almost touching the grinder's wheel. With that done, the grinder can be started and the drill fed into the wheel using the feed mechanism provided on the jig as seen in photograph 8. This will of course increase the projection but with it being such a small increase the effect in terms of the sharpened drill will be negligible.

 

Next, slowly rotate the jig backwards and forwards about the pin in the base a few times to complete the sharpening process of the first side followed by rotating the drill 180° and repeating the process for the second edge. I should add at this stage do limit the amount that is being removed as if too much is removed the drill may become over heated. Also, if you are establishing a new point on a broken drill then sharpening it by hand first would be a good idea.

Drill Grinding Jig, mounting
Drill Grinding Jig. Feed control.
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 8

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 9

Important

It is vital that the mounting surface is ridged as the assembly my deflect during the  sharpening process. This maybe causing the two edges to be ground unequally.

 

Similarly, do not place too much pressure on the jig itself  which may also flex and result in unequal grinding of the two edges.

Metalworking

Workshop Processes