I machined some plexiglass last night for the first time, and I noticed that there are some rough tool marks left over from the facing operation, only in certain sections. (Picture below).
Here are my machine settings for the facing operation
Machine: Shapeoko 4
Spindle: 800W brushless spindle
Tool: 6mm 3 flute coated end mill
RPM: 20K rpm
Feed rate: 70 in/min
Stepover: ~0.120"
Stepdown: ~0.120"
Finishing stepdown: 0.007"
Workholding: Double sided carpet tape
All 4 pieces were done on the same operation, and if you can see on the left side there are some white scratches. Those scratches are the “rough spots” left over by the face operation. The right half all looks/feels smoothWhat should I do to diagnose the cause of the artifacts? Or for those of you who have experience on finishing acrylic/plexiglass, would you just recommend wet sanding and polishing it? Thanks!
To make the edge better looking I have used a propane torch to burn off, or melt the fuzzies. Practice on a cut-off part first to get the right temp and speed to accomplish it.
Thanks for your response! Actually thinking back, I do remember upping the feed rate to 200% on carbide motion after my tool gummed up on the first pass. So the effective feedrate would be ~140 ipm with a 6mm 3 flute. I will try it with a 6mm O flute though. I actually get the same effects on Delrin as well, (the surface finish/tool markings changing midway through a facing path), but it’s just not as rough as with the polycarbonate.
Also what I found has helped eliminate fuzzy edges is running a 2d chamfer operation with a 45* V bit, but running the same duplicate chamfer operation TWICE. The first chamfer gets rid of the sharp edge, but forms a smaller fuzzy edge, and the second run gets rid of the smaller fuzzy edge for good. I’ve found that after the 2 chamfer passes, it got rid of 95%+ of the fuzzy edge.
Earlier today I tried wet sanding the plexiglass with 1000, followed by some polish and it turned out great. I think I’m going to just go this route.
Interesting that it’s in the same place on both parts. I think the most common cause is schmutz stuck in the cutter. I don’t have a dust collector, so I use spindle fans, or my mist cooling system with no lube to clear chips away.
The next, I think would be vibration in the part from not being held down rigidly enough.
