RepRap: Blog

As one might have expected, the signal-to-noise ratio caused by motor vibration makes attempts to use a piezo on the probe to detect the bed impractical. Still, had to give it a go. Getting well bored with this Covid thing by now.

I had heard potassium hydroxide was the electrolyte of choice for etching titanium wires. I tried it on my Nichrome. It is much less ... aggressive. I had to run it at 12V to get anything to etch, and then, well, I bring you The Demon Probe:

Totally unusable, but very eldritch. There's a lot of gnarly corrosion on there that won't boil off.

Conclusion: salt works better for Nichrome wire tips. But I will try to source some titanium wire and see what that does. Anybody got donations?

I just stuck a standard piezo disc on the stage (with a 1M2 resistor across it) and prodded at it with the probe. I'm getting a 0.02V response when the probe hits it with a positional accuracy of within 40μm - astounding considering the roughness of the piezo element and the fact that it's held down with a tiny piece of blue tape.

So, might be worth taking a side-trip to get some form of Z-height automation going on. So far the best algorithm seems to be to lower the probe until values happen, then lift the probe until they stop happening. There is a zero point in between, which complicates things and stops me just using it as a Z contact, and I have no idea what happens with fine probes (but I suspect it won't work so well...).

I guess the next step is to make a probe arm that holds a piezo with a tip stuck onto it and see what the heck happens. If anyone has been here already, please pipe up.

There is remarkably little noise introduced by the movement of the stepper motors.

I tried using the thickened resin again, and turns out manual flickering of the UV led is not accurate enough for a consistent result. Probably also temperature dependent. I noticed that the drawn-out lines of solidified resin warped and moved under my breath, but not a blowtorch draft, so the material seems to be very moisture sensitive in thin layers.

I got a thicker point which has heavy corrosion on it from not being cleaned properly after the electro-etching, and tried that as a dip pen. Just using a drop of resin off the end of a dental probe was too much material. The resin blobs when the point goes in, so using tissue paper I wiped most of it off, leaving a smeared layer approximately 0.3-0.4mm thick. This allowed me to dip the probe tip without causing resin to splurge everywhere.

Once dipped, I moved the tip away 1mm and lowered it to the slide surface. Not particularly accurately, just give or take 0.05mm. Raising the tip left a droplet roughly 100μm in diameter (don't know how thick yet). Moving back to the smear of resin, moving forward, new droplet, repeat, produced this line. Smear can be seen as darker area on the right.

 

An unforeseen problem is that the size of the smallest reservoir drop I can easily make is about the size of my work area, so I'm working around that by making the reservoir and manually aligning the probe with the edge of it before engaging the stepper drivers. Anyway, the Covid is starting to win again, so that's it for now.

Sorry folks, got the covids. Normal service resuming when I can figure out what normal is.