Monday, October 13, 2025
Testing The Level Of The Bed, Or Not...
I attempted a resin deposition run, unsuccessfully. This was due to a number of factors, most of which are visible in the following micrograph. This was taken with my phone through a microscope that cost me 30 quid from Liddell's, and focus is particularly blurry on the left, but it's the best magnification I can get:
This is an attempt at doing the "300μm" plot at a 10μm pitch using the acid/salt Nichrome probe. Why etch rather than deposit resin? Well, the height slope on the Y axis meant that the resin-dipped probe did not contact the surface, so I put down some Sharpie to see what was going on.
Setup Issues at 1000V/mm
During the Z-Touch phase I noticed that by dropping the probe speed to 2mm/min I could touch the foil reliably several times in the same location, but not if the tip was in resin. I think this is because the voltage will jump the air gap between the probe and the touch plate. Inaccurate rule of thumb suggests air breaks down and becomes conductive at roughly 1000V/mm so we'll go with that. The probe is at 5V, so at somewhere in the order of 5μm we'll start to pass current through it. The deceleration of the probe will stop it in less than 1μm, so by going sufficiently slowly the probe doesn't actually contact the foil much if at all - in air. On average.
The Y axis driver was noticeably (or rather, audibly) unhappy. There was insufficient tension on the anti-backlash bands, and the Drive Screw was periodically binding on the printed flexure assembly. I'll relieve the binding and increase the height of the bar with the backlash bands on.
Resin Issues
The main problem was making contact some distance from the touch plate. The next problem was trying to tell what a resin dot looked like amongst the scratches and debris on the slide. Illuminating clear resin for imaging is tricky. Coloured resin tends to have pigment in it, with a particle size of ~5μm. So, no resin results today.
Accuracy Analysis
Proceeding with the probe and a Sharpie, the actual impact points are pretty well distributed along the X axis. I'd call that 10μm or near enough, and I'd hazard a guess to say I could position at 5μm or better without too much trouble. Except for the backlash. The tail on the micron character should be under its left arm. It misses by about 5μm on the X axis. That's the only dot that is subject to backlash. So it appears I have that much backlash in the system.
Levelling Analysis
As the probe strikes the surface at a 60 degree angle to vertical, it will move across it at roughly 1.5x the distance of the over-penetration. From the image, after 100μm of movement on the X axis, the probe skids roughly 5μm sideways. So there is effectively a 1 in 30 slope on the slide. The dirty hack would be to shim up the left side of the 25mm wide glass slide by about 0.8mm, and the proper thing to do (eventually) would be to provide for bed levelling.
So, a few things to fix up, then we'll try again. I'll post a picture of what the probe tip looks like after all this when I take the machine apart.
