Short story:My dremel smoked up and doesnt start after trying to surface particle board in 1 1mm pass at ~30k dremel rpm. Machining time was around 40 minutes with a break in the middle to cool down.
Setup overview: 7x7 zen, stock leads, 4000 dremel spindle, using a dremel 5.5mm cutter with 10 flutes, LinuxCNC and TB6560 board.
Long Story:
I have a 7x7 zen machine and cut only foam on it since I had the machine until yesterday. I wanted to cut out a surfboard fin cad model I made in freecad with wood. My first step was to replace my foam "spoil board" with a harder spoil board. I cut out a rectangular piece of particle board that covered the cutting area of my machine(200mmx160mm). I wanted to try and surface It since it seemed a little higher in one corner then the other and the fin was going to be a 2 sided part.
Using CamBam I exported a g-code file that cut a line in the center of the board and then worked outward in rectangles( I didnt really have a preference how I did it other then efficient cutter movement and CamBam gave me that the easiest starting with a rectangle drawn with its CAD features). My machine will cut foam reliably at 325mm/min(except the Z axis which I limit to 150mm/min) so that's the feed rate I put in knowing I could slow it down with feed rate over ride. I have a dremel 4000 for a spindle and the most I ever ran it was 10-15k rpm and mostly below 10k, but just testing how the dremel cut a piece of plywood by had I knew i needed to up the rpm over 20k. My cutter was a 5.5mm square dremel bit with 10 "flutes" on it. I started the cutting out at 325mm/min with the dremel around 25k-30k. The initial plunge into the material seemed fine and it started cutting okay. I was watching the particle board to see if it was burning and It looked to be browning in some spots. Since I didn't notice the steppers skipping I brought the feed overide to %110. This made the steppers start to skip pretty bad so I dropped the override down to %80 just to be sure it wouldnt get thrown off more and I would only have to go back and clean up a few mm of missed particle board since the machine lost its reference. I brought the dremel up between 30k-35k since I slowed the cut rate down. I could defintely notice the cutter getting hotter and hotter so about halfway through the surfacing I paused the cut and let the cutter rest for 20-30 minutes and cool off.
The surfacing was going pretty poor from a machining stand point but I kept going just to see how it would turn out. I started the machining back up with the cutter cool again and let it keep going. Well a little while later with about 10-20% of the board to finish the dremel started to dig into the board and run downward till it burrowed and stopped. I hit the e-stop as soon as I could. Then smoke and a burning smell started coming from the dremel.
After I took the dremel apart I found one brush in perfect condition and another stuck inside the brush slot with its spring clearly damaged from heat and coiled into itself. It actually melted into the plastic cap that holds the brush spring in place. I am sending the dremel back for repairs.
I am just wondering since I burned the dremel out so fast that using it for cutting any wood is unrealistic or will it be possible if I just adjust my cutting feeds/depths and spindle speeds more conservative. I honestly was worried only about the particle board burning, skipping steps or the bit dulling from the heat and not thinking the dremel would fail. I knew I wasn't doing its long term life good by running it high but for one use within its "rated" speed I thought it would be fine. Again this is the only time I have done anything about 15k on this dremel and its only been used maybe 5hrs of run time if that across 2 years of owning it.