Twist drill speeds

Two questions concerning twist drills.

1) Do you calculate the speed of a twist drill the same as you would a lathe or end mill.

2) Do you alter the cutting angle dependent on the material or thickness of the material you are drilling.

1) Yes

2) Generally no - there are a wide range of drills available, but I use Dormer 4-facet drills as standard. I tend to buy stub drills for the repetition lathe, but they need to be left hand as well. If I need to drill a lot of holes in a given material I sometimes buy slow, or fast, helix drills as required.

Andrew

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

Eric, the smaller the drill the faster it needs to go, the larger the drill the slower it needs to go.

In general a standard set of drills will do all you need, the only exceptions if you are cutting tough stuff or Alu. or bronze/brass. Then you need to find out how to thin the web of the drill and again you may need a 1 set of drills just for non ferrous materiels.

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

Eric, If you PM me your details , I will supply you a drill manufacturers pocket hand book .

Trevor

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

Frank

Oh dear ..... slightly embarrassed

I select my medium speed for drills and my (geared) low speed for tapping and for the very occasional big drill. I have no idea what speeds they are.

My drills are not broken or burned and my holes tend to be reasonable round. So it works for me

Cheers - Will

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

Properly it's a ch-rat or church rat. These are even poorer than church mice and have to steal loaves of bread and are pursued over half the country by some French rat. Which is how they end up in the sewers. Meanwhile the other rats are revolting.

Actually, all rats are revolting.