Feed Speeds, RPMs, and Bit Life
"Make chips, not dust" — chips take heat off the tool, so to make bits last, set feed rates and RPMs to cut large chips. May 23, 2007
I need a little advice on what tool, RPM and feed rate to use when cutting through 3/4 import birch/poplar. I have a 5 hp Columbo spindle and my Shopsabre router has a max feed rate of 600ipm. I have been using a 1/2" 2 flute MC endmill bit. RPM at 18000, feed at 300ipm, plunge at 150ipm. Cutting all the way through in one pass, except small parts which I onion skin.
My concern is the bit seems to be getting too hot, so life is an issue. I just cut 16 sheets and by the time I got to the 11th sheet, the bit sounds a little dull and I had to slow down to 200ipm feed to keep it going without bogging down. The tool is from Integra and they tell me I should spin at 18000 rpm and feed at 600ipm. I can do that if cutting 1/4" deep dados, but not on the through cuts. What am I doing wrong? Should I be using a different type of tool, smaller diameter, maybe a 1/4" bit instead?
From contributor K:
I don't think you have enough HP. 300ipm @ 18000rpm is too slow. If you can't run it at 600ipm, try to play with your rpm. I would try to get it as low as you can without hurting the motor. Maybe 12000-14000rpm @ 300ipm.
From contributor P:
If the bit is getting too hot, I think you need to increase the feed rate. You should increase it until you start to see the cut quality start to degrade, then back it off a little. The larger the chips you form, the more heat you take off the tool. Going too slow causes the tool to heat up. If cut quality is not critical, use a single flute or a chipbreaker.
Let us know how it goes.
From contributor T:
Here's a formula to help get your speeds and feeds dialed in.
(chipload) x (# of cutting edges) x (rpm) = feed rate
From contributor A:
Try a 3/8" 2 flute cutter. The smaller diameter may allow you to boost the cutting speed to keep the bit from burning. I cut mostly 3/4 ply at 600ipm and 16000rpm, getting 100 plus sheets per bit.
From contributor J:
I'm having the same problem that the questioner is having with burning, and when the bit gets dull, it starts slipping inside the collet. I think that I am probably cutting too slow also. I'm using a 2 flute 3/8" straight bit making 2 passes at about 200ipm and cutting 3/4 birch and maple running a 8hp hsd spindle. Are you using a straight flute upcut or compression, and what size router are you running? Are you making more than 1 pass?
From contributor G:
You are burning up your tool, because you are recutting the chips. Reduce your RPM to 12K. Longer tool life will be the result. At 600 IPM, your RPM should be 15-16K. Most firms (and I do mean most) reduce the feed speeds; they should increase feeds or reduce RPM. Remember, make chips, not dust.