First aluminum fail, figuring out why

Yes, I used a 3/16" 2-flute ZrN bull-nose endmill. My parameters are:

  • 0.00125" CPT @ 20000 RPM
  • 0.015" deep
  • 40% optimal load

I have trammed my machine and surfaced my wasteboard. I use double sided tape for workholding coupled with some clamps.

Any suggestions?

0.075 is too much for opt load. I usually don’t even go past 0.060 even on full kill. Doc should be much much higher

Go deeper doc and cut opt to 0.050-0.030

Calculating chip thinning is very important when using small adaptive stepovers.


Got it. I will try that on Friday when I get some shop time.

When calculating chip thinning, I need to shoot to have an optimal chip starting thickness, right? I’ll check out your calculator above.

Edit: Yep, read up on chip thinning. Thanks for the resource.

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Sorry I posted about it twice, nobody ever really said anything to me about it so I try to pass it on. Was doing 10mm doc the other day and it helped quite a bit.

Usually I’ll use that calc to see the actual chip but the recommendations they give can get a little up there.


Thanks Vince on your recommendations! I cut much deeper now. Optimal load=0.04, CPT=0.0012 (with chip thinning factored in), and DOC=0.1. I also found that my 1/8" carbide endmill works well at DOC=0.075. Then I tried slotting with the 1/8" at lower DOC and filled up the flutes with aluminum. I think lubrication would help a lot.

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