Speed Matters 20mm/min vs. 5mm/min & Z Touch

Couple of important things about this otherwise ordinary-looking logo attempt, scratched with a hypodermic tip on a Sharpie-coated glass slide by Maus. First off, the top one was printed with an X axis speed of 6mm/s and a Y axis speed of 20mm/s. The bottom one with X&Y set to 5mm/s. So there appears to be a speed limit on smoothly driving flexures and that needs investigation. Mind you, the bottom one looks pretty darn good, though the corners are not yet as sharp as those from the OpenFlexure stage.

Second off, these were done by getting the probe height using a Z Touch plate. This was made by sticking aluminium foil to a glass slide. The procedure was to take a clean glass slide and drag lines of a very small amount of 3D printer resin around one end of it in roughly a 25x25mm patch. 25 micron aluminium cooking foil was then placed on the resin. A piece of 80gsm printer paper was laid on that, and rubbed hard with the base of a smooth, thick-walled polyethylene bottle. This created a very flat foil surface, and exuded much of the already small quantity of resin.

Microscope slide, left side coated with aluminium foil. Black mark is Sharpie marker. 0.4mm object engraved at 47mm mark, just below centre line.

The underside of the slide was then exposed over a 4W UV LED to cure the resin film. This foil acts as the Z Touch plate, and when connected to the GRBL board inputs together with the probe wire, the CNCjs Probe Touch function operated normally. The touch plate thickness was set to 25 microns, but this may not necessarily be the true thickness of the foil for many reasons. Repeated touches in the same spot eventually gave CNC readings consistent to +/2 microns though the true error is unknown.

Note: Acceleration of the Z probe is problematic for Z Touch operation. GRBL will only decelerate at the same rate as the maximum acceleration value for that axis. Basically, when the probe touches, it takes a while to slow down. I have set the Z axis acceleration rate to 1mm/s/s and at this rate it does not deform the foil. X & Y are currently set to 0.1mm/s/s as an estimated initial starting value for testing.