1/ Half the time you can't be bothered to change the belts so spend ten times as long watching a small drill thinking all the time 'I should stop and change up but I'm not going to cos the next drill is bigger'. Best use for a 3 phase with speed control.

2/ Amateurs don't. Who can afford multiple drills. In theory some people suggest dulling the cutting edge for brass to stop it snatching but that would mean resharpening unless you have 2 sets so who is really going to do that.

If you want a slow spiral drill just buy a cheap Chinese set and watch it untwist itself when it hits a hard spot

A typical bench drill will take bits from ~1mm up to 1/2".

You can send ages studying charts and formulas but if you select the pulley sizes roughly in proportion to drill size with top speed for anything smaller than 1/8" and don't expect to drill at the larger sizes in one go, you won't go far wrong.

Neil

<edit> Chrats? What on earth is a chrat, neil?

Edited By Neil Wyatt on 28/08/2015 10:47:33

Good number to remember :- 1000 RPM 1/4" mild steel, other sizes pro-rata, ali faster, cast iron slower.

Frank

I have a Ryobi pillar drill with infinitely variable speeds from 400 rpm to 2500rpm. These are purely mechanical being belt driven expanding cones controlled by a lever whilst it's running. It has a digital readout.

It's been very instructive altering the speeds while drilling with different types and sizes of bits into various metals. I've found very little correlation between published drilling table suggestions and what actually works best!

Roger