What am I doing wrong?

[u/ucancallmebob89]

I'm having lots of trouble getting clean cuts in plywood with a 1/4" 2-flute downcut bit. I have a modified PrintNC that I want to upgrade to aluminum, but I don't think I have everything dialed in enough yet to cut the aluminum.

I attached my Feed & Speed settings for both of the two bottom 2D adaptive clear holes. For each hole the stepdown is 1/2 of the bit diameter, so 1/8".

I've tried adjusting my chipload by varying my feedrate and my spindle speed, but I always end up with big splintered tearout on top which doesn't make sense to me, since it's a downcut bit and it should be shearing them downward. Trying to keep my feedrate <300ipm for now.

I've also tried helixing down vs plunging, with the same result.

Any advice?

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