Chalky white, jagged cuts into cast acrylic

I’m having a hard time determining what’s causing an intermittent problem with shallow cuts into cast acrylic using the default settings in Easel (for acrylic) and speed of 1 on my 611 ( I know, most seem to say that that’s still to many RPMs for acrylic). Anyway, sometimes I get the cleanest cut of this font at the same depth, and sometimes it’s ragged and ‘chalky’ whitish and just not attractive - and the bit seems to leave ‘dots’ of depth in places (uneven in other words) You can see two cuts of the exact same thing done minutes apart (bottom one (the offender) is a bit fuzzy, apologies…but you get the idea). So I don’t feel like it’s a dull bit either. It’s like I can get one of these two results minutes apart with the exact same material and settings. Any clue what might be causing this?


That is melting/rewelding. Is the worse if the two the second one you cut and was it literally minutes? Because your bit is going to keep getting hotter without time to cool down between jobs. However that is not your real problem, it should not be getting that hot to begin with. Even the better of the two images you posted looks pretty bad to me. Speeding up your feed rate is your only option since you can’t slow down your spindle. If that doesn’t do it your bit is dull.

Thanks very much. Just the verification that it’s melting and not something else really helps. I’ll mitigate with better cooling and increase feed rate. Much appreciated!

I am looking into a VFD to have on a swappable mount. I am cutting so much plastic lately it will be a worthwhile investment.