Mini mill RPM

[Taximanny]

I'm never done any milling before and had some questions.

Just purchased HF mini mill.. I got it set up and tried a test run on some brass.

Here's is the scenario
.04 brass liners
I'm using a 4 flute 3/8 end mill
I removed about .005 off of liner to relieve it. Give or take a couple thousandths.

The rpm I used was 1100 is that to slow or to fast ?
( I feed it super slow since it was my first time)

It came out really nice.

But I'm not understanding the milling charts.
One chart said 700 and another says 1170

So those of you milling out your brass liners what RPM do you use ?

Also what might be the best RPM for stainless liners?

Thanks
Manny

 

[SBuzek]

HSS or carbide end mill?

 

[Boogaloo]

Rpm is dependent on the material being cut, type of cutter (hss vs carbide) and the size of the cutter. Generally speaking: softer material and smaller cutters use higher rpm. Most charts will give you a recommended range of surface feet per minute for a given material and cutter. Then convert to rpm by multiplying by 12 (feet to inches) then dividing by circumference of your cutter (pi*d).
A quick shortcut that's pretty close is rpm=(4*sfm)/d
Hope this helps.