Milling Speeds for end mills

I just gave a generic speed for "steel" using HSS to show Chris how the numbers work in the formula, Speed could have been anything from 50 to 150 feet per min ( 15-50m/min) depending on what steel and type of cut, type of cutter, any coating, etc as per my previous comment. If you take a look at the likes of Tubal Cain in Model Engineers Handbook he gives us 2000rpm for a 1/2" cutter in free cutting steel in which case 800rpm is a bit tame

Treat published speeds as a starting point and adjust to suit machine and job in hand and as I tend to find with teh smaller machines they are best run towards the fast side but with reduced DOC and possibly feed to keep the motor in the sweet spot and to compensate for their lower rigidity.

Have scanned pages from Tubal Cains 'Model Engineers Handbook edition 2' if it's of any help.

George

Edited By mechman48 on 24/10/2020 16:48:00

There’s fundamental problems with Tom’s tables in the past I have used them but i became exasperated with my copied tables until I realised the error
why? His speed for a 1/4” 4 tooth endmill is 960 in steel with 1 -3/4” feed , yet for a slot drill it lists 1600 rpm and a feed of 3” min. He has the headings the wrong way round! If you follow this point then the tables are very low in cut per tooth

using the 4*cs/ dia yields 1600 rpm ( cs= 100 fpm) Using a feed per tooth as recommended between 0.0005” and 0.002” this yields a feed rate of

fr= rpm x no of teeth x feed per tooth

= 1600*4* 0.001= 6.4 Inches per min.
Tom’s numbers are at the bottom of this range, and he states the tables came from Clarksons Autolock Chuck data.
with more modern spiral endmills with various coatings and the increasing use of carbide cutters in the home workshop, his tables aRe becoming outdated

Edited By Zan on 06/11/2020 21:25:40

Missed the link. Presto information in the “Counsellor” Pages 48 and 50

https://www.presto-tools.co.uk/Downloads

I think you have a misprint, TC gives 2000 rpm for a 1/16" cutter, not 1/2"

Duncan No misprint just you have misread it. Mine is what I said yes he gives 2000rpm for a 1/16th cutter but not in group "D" which is what he classes free cutting steel as, does not even offer a speed for a 1/16" cutter in that.

Edited By JasonB on 07/11/2020 07:14:47

.

That said ... The asterisked footnote is worth reading

MichaelG.

Whoops, I agreed with what Mick meant rather than what he typed!

Dave

Sorry Michael I should have said "does not offer a maximum speed" not to be exceeded if the machine is capable.

He gives it for the 1/8" & 3/16" with the asterisk but not the 1/16th, probably did not want to muck up the tabulation when the speed got into six figures.

Having arrived at rotation speed to achieve the correct surface speed for the cutter material mand the work material, the bother factor to take into account is the feed rate.

For each type of cutter there is feed rate determined by the number of teeth, and rotation speed.

An End Mill will probably have a feed per tooth of 0.002" (0.050 mm ). So running at 1,000 rpm with a 4 tooth cutter will result in a feed rate of 2 inches (50.8 mm ) per minute.

Feeding above the ideal feed / tooth will wear the cutter, and even break it if sufficiently excessive.

Feeding much too slowly will cause the cutter to rub, and the local heating may well soften and blunt it.

The feed rate will affect the surface finish, coarse feeds, as you would expect should produce a rougher finish. This is acceptable for roughing where the object is to remove metal as rapidly as possible. For finishing cuts, the depth of cut and feed rate will be decreased.

Carbide tooling requires surface speeds and feed rates that differ quite markedly from those for HSS.

Howard

Feedrate = feed per tooth x number of teeth x rpm

With the figures above I make that 8"/min.

It's surprising how big a chip load one can use without breaking the cutter. If I get careless when climb milling the cutter will drag the table. My mill is pretty worn, probably 12-15 thou backlash on X. When the cutter grabs there's a bit of a kuthunk but the cutter shrugs it off and everything continues as before.

Andrew

Ah yes I'd misread it, but note that TC says immediately below the table that 'for milling treat F.C steel as C, so he recommends 480 rpm. 2000 rpm on a 1/2" cutter is 262 ft/min, which is very high for even FC steel.

Edited By duncan webster on 08/11/2020 01:16:20