CNC - Tooling Parameters cutting HDPE

[mhuff777]

We have a CNC with max rpm of 18,000, and max Feed Rate of 350 inches/min; and using Amana Tool 51404-K Solid Carbide Spiral CNC Router Bit O-Flute Up-Cut (1/4" End Mill) to mill out HDPE.

From my understanding, we need to keep the Chip Load between 0.006" to 0.009".

My initial settings are:

• Number of Flutes: 1

• Spindle Speed: 18,000 rpm

• Feed Rate: 120 inches/min

• Plunge Rate: 10 inches/min

I wanted to check before we ran this.

[tomgardiner]

Your numbers check out but...
I would program a test run with theses parameters with the exception - raise your plunge rate to 80 - 120 in/min. Ramp in at 45°.
Also, the ideal chipload is often not the key determinant for successful cutting. Work holding, machine rigidity will be more important. There is a significant lifting load with an O flute bit so depth of cut might have to be adjusted.
HDPE cuts like butter and doesn't tend to weld to the cutters. Adjust your feed speed to get the right compromise between time and finish quality.

[adze_cnc]

With my machine your average chipload calculator results of between 0.07 and 0.010 inch chips works fine. The last three HDPE projects cut I cut were with a 1/4" bit and were two white HDPE (a 4.5 inch square clay extrusion die, large legs for holding an acrylic splash barrier) and long black HDPE frame borders.

The "feeds and speeds" were (pass depth of 1/4" in each case):

1. extruder die: 18000rpm; 120ipm feed and ramp; 0.0067" chipload (small details and a need for a smoother edge)
2. barrier legs: 24000rpm; 200ipm feed and ramp; 0.0083" chipload
3. black HDPE: 20000rpm; 200ipm feed and ramp; 0.0100" chipload (coloured HDPE tends to be less soft and seems to handle larger chips)

I generally do longer ramps. A previous post mentioned 45 degrees (the length would be your bit's pass depth). I like a 2" ramp for smooth material engagement's sake.

One thing that can help is to set your "Do separate last pass" allowance to 0.006 inches or so. This helps avoid odd cutting patterns on the material's edge. I wish I'd kept a certain feed and speed setting that produced a nice cross-hatching.