I’ve been getting a very poor finish on a small delrin part (photos of part and fixture attached) and am wondering what is causing it. The whitish markings show up at the same height no matter what parameters I’ve changed. The also show up on 3 sides of the part but not on 1 side. There are pretty much in the same location on every part I cut.
I’m using a 2 flute 1/8th carbide EM (TiN coated). It’s a 0.01” finishing pass, 0.41” DOC, 5100 RPM and 60 IPM. I’ve varied the feeds between 40 and 90 and tried reducing the speed to 4800. I’ve varied the WOC between 5 and 10 thou, tried cutting it in 2 passes instead of one full depth pass and have tried two different carbide end mills. The only way I have been able to eliminate the marks is by moving up to a 0.25” EM going at 5100 RPM and 90 IPM. This produces a good finish, but I have to use an 1/8” EM to get a proper radius on the outside fillets.
Any thoughts on what could be causing this? I'm thinking that my surface speed is just way too low (167 SFM for an 1/8" EM at 5100 RPM), but how to I fix this when I can't increase my RPMs any more?