The MPCNC isn’t the most stable of CNC machine tools, given its large masses and 3D printed structure. My early plotting pen tests suggested speeds around 250 mm/min were appropriate:
Diamond drag engraving produces a thinner line and makes the wobbulations more obvious:
Another test showed similar results:
Slowing down definitely reduces the shakes:
Producing the best results takes quite a while:
Similar results on another test:
Those “mm/s” labels are typos; they should read “mm/min”. Plotting at -1.0 mm on scrap CDs and DVDs produces a downforce around 200 g.
Eyeballometrically, 100 mm/min seems fine, but 50 mm/min (I’d likely use 60 for a nice round 1 mm/s) eliminates all the shakes.
Smooth curves, like Guillloché patterns, can run much faster, because they don’t have abrupt direction changes. This 3-½ inch hard drive platter has text engraved at 100 mm/min and the pattern at 600 mm/min, both at -3.0 mm for 300 g of downforce:
A closer look at the text:
And some digits:
When I want to brand an engraved CD, this will suffice:
All in all, the MPCNC engraves much better than I expected!