View Full Version : Need Help! Milling a plastic with a CNC 770 milling machine

Edmond Young
07-10-2013, 04:22 PM
I am currently doing microfluidics research and kind of stuck on this situation.

I am using a 0.79mm or 1/32 inch tool to mill a "bean" shape that is 1.2mm wide on a Polystyrene sheet.
However, my tool keeps breaking after milling one "bean" shape on a polystyrene sheet.

I used 7000rpm and 250 mm per min.

Can anyone of you give me a tip or method that I should take to successfully mill without breaking the tool?

07-10-2013, 04:26 PM
What's your depth of cut?

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Edmond Young
07-11-2013, 12:51 PM
The depth is 0.5mm, I did some research online and apparently I need a faster RPM, but my milling machine can only go up to 10200RPM
Can you recommend ideal RPM and feed rate ?

Thank you!

SBC Cycle
07-11-2013, 01:15 PM
How many flutes are on the tool?

07-11-2013, 05:30 PM
Ideal would be like a router. Maybe 25000 RPM.
You may be breaking the tool due to heat by going that slow and that low on rpm.
That is about 10 IPM, which is very slow for plastics.
Put some coolant on it and speed it up as fast as you can on RPM and I'd say at least 25 IPM. Maybe 50 IPM.

Edmond Young
07-11-2013, 11:21 PM
4 flutes

07-11-2013, 11:44 PM
Switch to two flute, your probably melting the plastic.


precisebits has a nice write up on finding ideal feeds and speeds for small bits too.

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07-12-2013, 12:18 AM
Also, of you can switch to delrin or abs, they both machine better than polystyrene.

I have cut 500+ parts (5x15mm dimension)from 1.5mm abs and delrin sheet on the same bit. 18000-24000 rpm 15-30 ipm.

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SBC Cycle
07-12-2013, 09:55 AM
I suspect the 4 flute tool is your problem. Try a double as suggested or possibly even a single flute endmill (although at that size it may be very easy to break).

You can machine plastics with lower speed but the finish will suffer slightly, just keep your speeds and feeds relative - keep that tool moving and ejecting the hot shavings.