Help! I keep breaking 1/16 endmills

My cuts are clean but I’m busting bits too quickly for my settings to be right.

I am very likely being too ambitious with my feed rates and DOC when using 1/16 end mills, but I want a little better resolution than what I get with a 1/8 endmill so I need help because I can’t make a 1/16 end mill last more than 5 minutes.

This is me cutting 6mm lexan…
Spindle is approx 20k RPM using a DW660 and a rheostat.
2 flute up-cut 1/16 end mill
DOC 1mm
Feed rate 20mm/sec
Plunge rate 6mm/sec

My calculations say to run around 30mm/sec and the bit simply is not going to hold up to that. I am skittish in slowing down the spindle speed because the rheostat cuts voltage and that builds heat in the motor. It is my understanding that going too slow makes for a less clean cut in lexan.

So I’d love to hear what others are using or where you think I’m screwing up.

The following should be a link to the video:

You plunge is probably too fast.

As for the rest, the best way to approach a cut is keep everything the same and only vary the Depth of cut. 20 is faster than I ever cut but if you want to do that just take much smaller passes, or cut all the way through and use adaptive/tricoidal.

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