CNC Tool Overheating and Fire Risk

      Tips on CNC feed rates and rpm's to reduce the risk of ignition in composite panels. November 23, 2008

We have two CMS routers that are 10 years old - spindle speed of 16000 rpm's and feed rates up to 1200 inches per minute. We do nested base processing on our machines and when we are machining patterns out of some of the newer "green" materials, we experience some burning of the flake core and are very concerned about having a fire in our dust collection system. We typically run 3/8" up/down spiral compression bits at around 600 inches per minute. The spec on the tooling calls for 20,000 to 21,000 rpm spindle speed, but we are only capable of 16000. Is this the problem? We take delivery of new machines beginning in August (which have the capability of the higher spindle speeds) but I am concerned about the burning issue from now until then. This happens whether it is brand new bits or re-sharpened bits on the very first sheet.

Forum Responses
(CNC Forum)
From contributor J:
Two flutes? 3/4" material? If so, I would start at 528IPM. You're close at 600IPM. Are you getting (fine) sawdust? If yes, increase the feed until you get small shavings. I would guess the burning is from running too slow, unless there's something wrong with the tool geometry. In my opinion, a recommended RPM without rate is useless.

From contributor M:
I have noticed that when the chip load is not terribly unreasonable, like yours, and there is burning, it can often be traced to a poor re-sharpening service. Try new tooling at the same feed rates and see what you get.

From contributor G:
You are running at a good feed speed and rpm's for your chip load. Older machines do not have the same capabilities as newer machines, with regard to acceleration and deceleration. With older machines it takes longer to decelerate in the corner (tool dwells). This may be one problem. Lower your RPM to 15K.

From contributor B:
Try using a temperature gun on your bit as soon as it lifts out of the cut. It should be well under 200 degrees F and should cool rapidly. If it's running too hot, increase the feed rate. If you can't do that, lower the RPM. You need a heavier chip load. Getting the bit into fresh wood will actually cool it. Wood and paper burn at the same temperature and that is 451 degrees F. If your bit is anywhere near 400 degrees F you could have a fire. I use these to determine when the bit is getting dull.

From contributor J:
"Lower your rpm's to 15K." He posted that his RPM is fixed at 16,000...

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