How much force does it take to mill steel?

[Billhill]

I'm scratch-building a CNC mill, and need to know how many foot pounds it takes to push the cutting head through CRS and tool steel, aluminum and brass.

I understand that the cutters need to be at their sharpest, and that the tool path should take off small chips (small depth of cut), and that the X-Y-Z motors should not be rushing along.

Any help will be gratefully appreciated, even from manual machinists who can guesstimate their forces.

While you are at it, give me some ipm figures to shoot for, broken down by materials.

Thanks

[protman16]

Billhill,

Got to hthe Kennametal site and look for their horsepower and force calculator.

[Jason3]

Sure - you don't mention what size cutters you'll be using, so for say, 10 mm (3/8") using the following parameters: Side milling - 1.5 x D DOC, 0.1 x D stepover, slot milling 1 x D DOC, the load on the cutter is about:

Aluminium - side milling ~ 250N, torque load 0.16Nm, slot milling ~ 600N, torque load 0.4Nm

1045 Steel - side milling ~ 600N, torque load 0.4Nm, slot milling ~ 1200N, torque load 0.6Nm

For Alu, side milling, the above is based on 3750 RPM & 1000 mm/min feedrate, slot milling 3150 RPM, 300 mm/min feed rate.

For 1045 Steel, side milling - 1400 RPM, 450 mm/min feedrate, slot milling 1250 RPM, 100 mm/min feedrate.

All figures are for Carbide tooling. What size machine are you building? - the figures above are a pretty decent load for a desktop machine, but easy for a knee mill... You can reduce your DOC to reduce the power required, but don't reduce your feed too much without reducing your spindle RPM or your tool life will suffer. In Aluminium, you'll want coolant at those speeds, or the chips will likely start to weld themselves to the cutter. To cut Alu dry, you'll need a fast spindle - I use 25,000 - 30,000 rpm and a 0.02 - 0.04" DOC, and feed at 100-150 ipm for roughing with a 1/4" 2 flute carbide cutter.

As to the spindle power required, I think you'd be looking for about 1 Hp to be safe with those cuts. I know from a simple exercise a couple of days ago a 50 mm face mill in Alu at 4200 rpm, 0.1" DOC and 40 ipm needed 3 Hp.

Hope that's some use!

Best regards,

Jason

[Billhill]

Jason3
Thanks a lot for the great info.

Aloha!
Bill