Archive for July 17th, 2019

MPCNC: Diamond Drag Engraving Speed Tests

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:

MPCNC - GCMC Text - 250 mm-min
MPCNC – GCMC Text – 250 mm-min

Diamond drag engraving produces a thinner line and makes the wobbulations more obvious:

MPCNC Engraving Speed Test A - 600-900 mm-min
MPCNC Engraving Speed Test A – 600-900 mm-min

Another test showed similar results:

MPCNC Engraving Speed Test B - 700-900 mm-min
MPCNC Engraving Speed Test B – 700-900 mm-min

Slowing down definitely reduces the shakes:

MPCNC Engraving Speed Test B - 100-300 mm-min
MPCNC Engraving Speed Test B – 100-300 mm-min

Producing the best results takes quite a while:

MPCNC Engraving Speed Test A - 50-200 mm-min
MPCNC Engraving Speed Test A – 50-200 mm-min

Similar results on another test:

MPCNC Engraving Speed Test C - 50-150 mm-min
MPCNC Engraving Speed Test C – 50-150 mm-min

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:

MPCNC Engraving - Guilloche drive platter test
MPCNC Engraving – Guilloche drive platter test

A closer look at the text:

MPCNC Engraving - hard drive platter - detail A
MPCNC Engraving – hard drive platter – detail A

And some digits:

MPCNC Engraving - hard drive platter - detail B
MPCNC Engraving – hard drive platter – detail B

When I want to brand an engraved CD, this will suffice:

MPCNC Engraving - CD attribution text
MPCNC Engraving – CD attribution text

All in all, the MPCNC engraves much better than I expected!

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