Drilling...help!

^ Good advice. My pillar drill pretty much stays in the lowest possible speed 90% of the time, as most of the holes are ~8mm and up.

One technique I've started experimenting with is 'peck' drilling. I found that even at a slow speed, drills can get quite hot quite quickly if you're putting enough pressure on for them to cut cleanly. Rather than lessening the pressure - which can cause the drill to rub on the workpeice without cutting it, eventually work-hardening the metal (esp. if it's stainless) - I briefly apply a high enough pressure before lifting the drill from the workpeice again. Repeating this keeps the drill working but without overheating. You do need to make sure that the drill does some cutting at the base of the hole. It looks a bit like a bird pecking at something - hence 'peck' drilling - and is widely used in CNC machining where there's no-one to keep an eye on the swarf.

Technically, it should only be required when drilling something that doesn't produce nice clean sprials of swarf (some steels, aluminiums, etc.) but where you're drilling by hand with not-quite-right drill bits - esp hand-sharpened ones - without a coolant spray (perhaps in a drill press that won't go slowly enough), I find it useful.

A video of CNC pack drilling, just to give you an idea.


I do something similar by hand.

To determine the correct pressure is a question of experimentation. Start applying a lot, with a sharp drill, and you should get long, curly swarf. If you reduce the pressure until the drill stops 'biting' and starts just rubbing over the surface, you've gone too far and need to apply more pressure.

Finally, proper cutting fluid does make a difference - not that cheap though.

Another thing to remember.

Big drills don't like cutting through solid material.

Best to start with a pilot hole, about 3mm and then work up in reasonable jumps, say to 6mm before finishing with a 10mm.

Anything over 1/4" I always pilot drill first. Larger drills need slower speeds, it's all about surface speed of the work piece/tool cutting edge. I could tell you all the recommended speeds/feeds quoted from Dormer, but that would be a little dull!
As a rough guide, up to 1/4" dia 1000rpm approx. 3/8" 750rpm, 1/2" 500rpm. all speeds are approx and if you're getting 'chatter', ie; vibration from the drill bit, then slow down more.

If any lube is used, you'd be better using a cutting agent, such as those used for thread tapping. Ordinary oil, whilst reducing friction on the sides of the flutes, can also have the same effect on the cutting edge, which is obviously not desirable. You want the drill to cut, not slide over the surface.

I really need to learn how to sharpen drills. Can anyone point me to a idiot's guide to doing it please?

In that peck drilling video above, is he not drilling with a straight fluted endmill and hence lifting the chips out manually?

Also, I read somewhere that masonry bits are actually good for boring harder steels but they need to have an edge ground on them first and that ordinary silicon carbide wheels are no good for them. Could anyone here shed any light on that? (And can they be sharpened with an aluminium oxide flap wheel?)