Further question re large drills

Some of the batch of large drills that I purchased have been turned down on the shank. The turning is very rough and I would like to give the shanks a decent skim to get things right. These shanks are seriously rough, such that I doubt that a small fraction of the total area of the jaws of a large drill chuck will be in contact with the turned down shanks! Some of them are indeed running out of true anyway.

So is this a 4 jaw job and clocking it up to run true before skimming. Sounds like a self answering question, but I usually make some incorrect assumptions. So before I go ahead, can someone confirm this is the correct procedure?

Thanks,

Andrew.

Four jaw and clock is probably the best option with inevitably limited home shop facilities. Mounting needs a bit of thought to get a clean grip on the drill, especially with a large drill in relatively small chuck jaws. May well be worth making some pads to extend the jaws a bit so all are cleanly on the flutes. But that isn't as easy as it sounds. Probably some form of location needed to ensure they don't tilt.

I've got loads of kit and better ways but with limited equipment would probably make an alloy sleeve with a single slit in it to compress down and grip the smallest drill then bore it out for each successive drill size. Need to fill the slit for each bore out of course.

Rough turning is due to Bubba thinking its an easy job and just grabbing in the three jaw. Inelegant, unbalanced, partial gripping on the flutes meant it was unstable.

Coming to the conclusion that every time you think "Ha, nice easy job." you should walk way, get thinking cap and cuppa then sit down and properly think it through. I pretty much never have issues with the obviously harder work that clearly needs thought. Its the "clearly obviously easy" stuff that has the gremlins sharpening claws and fangs in anticipation.

Clive.

Hi Andrew,

I have turned down the shank of large drills to 13mm so they would fit in my drill chuck. I used a 4-jaw independant chuck and a dial indicator (as suggested), the drills work fairly well.

Thor

I successfully turned down the shanks of a number of square taper shank drills some years ago so as to be able to use them in a standard drill chuck. As I recall, the method was to chuck a suitable blank in the lathe and bore a hole a close fit to the drill which was then forced into the hole by pressure from the tailstock centre in the pre-existing female centre in the drill. The shank could then be turned, as it were, between centres.

I have no doubt other ways would work but I had in mind that the drill has a tiny taper along the fluted section and holding it directly in collet or chuck would be less satisfactory.

Edited By ega on 16/09/2017 17:29:13

I did that too some time ago and it work out well.Not too difficult and cheap !

Why not make a split brass bush to suit the drill, and support the shank with the centre if it is still there. It may not be so easy to hold the 2 flute drill with is spiral flutes in a 4 jaw.

Chris Gunn

Would a collet chuck be a better option?

I don't have collets that big Vic!

Andrew.

Assuming the centre hole in the tang is still retrievable, sharpen the drill first, so the pointed end is actually in the middle, and drill a small bevelled hole into a spare blank arbour to fit your headstock.

Use this to locate the sharp pointy end and turn between centres.

Bill

Your re-turning can help trueness but not friction between shank and jaws.

Contact area does not matter very much ,but jaw forces do.

Edited By Niels Abildgaard on 17/09/2017 06:39:01

...Or bore a hole about half a diameter deep and a light drive fit on the drill's circular land in a bit of scrap material in whatever chuck you happen to have in place. Use the tailstock centre in the drill's tang hole to push the point into your bored driving plug, and you should then run very concentric, for a series of light cuts down to a diameter suitable for a drill chuck.