Overheating in Short Cuts

      Maintaining the right RPM and bit speed gets tricky when the cuts are short. February 28, 2012

Question
I have tried a 2 flute straight cut at15,000 RPMís and 500 IPMís, a 3 flute upcut at15,000 RPMís and 500 IPMís, and a 2 flute straight cut at18,000 RPMís and 500 IPMís. The cut is small - about four inches long, so it barely gets up to speed. Does anyone have a good suggestion to make this sort of cut and keep the tool cool?

Forum Responses
(CNC Forum)
From contributor D:
My machine has a maximum acceleration of 0.10G's or 38.61 inches/sec^2. On a four inch run it takes 0.90 inches to get up to 500 IPMís and then another 0.90 inches to stop - a total of about half the length of the cut. In terms of time, it spends about 10% of the time at 500 IPMís and 90% of the time either speeding up or slowing down. I don't yet have a good handle on what the best balance of slow/fast is yet, but I'd bet that 90% slow isn't helping. If it were me, I'd reduce the RPMís or try a single flute bit - upcut if you can get it.



From contributor C:
You need to double the feed speed or cut the RPMís in half. Typically in particle board on a nesting CNC a 2 flute should spin 16k rpm at 25 MPM (meters per minute) or around 950 inches per minute.


From the original questioner:
Contributor C Ė thatís faster than I run my 3/8 mortise compression through 3/4 melamine. It sound like the bit could break at that speed. I started cutting 1/4" deep in one pass and then I changed it to 1/8 passes to a 1/4" deep total and the bit was still getting hot. I think I need to try a single flute.


From contributor C:
I missed the 1/4" part. Slow the RPMís down until you no longer have a nice cut. Then increase the RPMís by 500 to 1000 RPMís. The bit is getting hot because it's double cutting. Talk to the bit manufacturer.


From contributor H:
The problem is what the others have said. The machine cannot ramp up that quickly. So basically you have to lie to the machine and say you are running 800 to 900 IPMís even though you are not. Or decrease the RPMís. Itís one or the other.



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