RepRap: Blog

The blog has stopped accepting images for unknown reasons (bug-a-minute here), so this one is pointing to my Mastodon account on the NZOSS server. I hope it works. If it vanishes, sorry, I have the original.

 

What you should see here is four etched probe tips, numbered, etched from 0.3mm 316L SS wire. #14 was made a couple of days ago before my Z Axis died. That was given a 20 second roughening etch, then the GCODE-controlled etch as per the github repo /utils directory. It has a smooth ogival point.

#15 and #16 were the ones that ended up malformed due to the misbehaving Z Axis. I cut the tips off, and re-etched the wires using the same GCODE as #14. These display a significant stepped profile to the point. Not what I was looking for.

So I wondered. What effect is the roughening etch having on the point profile? So I etched #17 with the same GCODE as #14 but did not do a roughening etch on it. The ogival profile is very good.

All of the probes display a slightly roughened area about 0.1mm behind the tip. This is unplanned but fortuitous. I will experiment with #17 to see if the roughening process is worthwhile when using the sodium chloride etch. The nitric acid roughening etch certainly soaks up the resin, but I have not seen any of this behaviour on the sodium chloride etched tips unless they are over-dipped. Over-dipping is not good for accurate resin deposition as it results in a roughly spherical blob held on the tip by surface tension rather than a film held by capillary action.

Anyhoo, now have tips. Next step is to mount them to the Flexured Probe Holder I printed earlier. 

I took the Z axis off and followed my own instructions https://github.com/VikOlliver/RepRapMicron/wiki/Probe-Tip-Fabrication-And-Assembly to build three probes. When I started doing the second one, it was pretty obvious something was wrong because I had to raise it much higher above the etchant to break it clear of the meniscus. They came out like this:

 

 

Hmm, maybe one is usable but it looks a bit too sharp. After poking around at the Z axis I determined that the locknut at the top of the ZAxis Drive Screw was no longer in the right place. It seemed tight enough. It's possible it released and then re-tightened itself. It's also possible that the Flexure Coupling on the stepper motor has failed or compressed, or that I never had it right to begin with and just got lucky.

Anyway, it is re-tightened. I'll just chop the ends off and try again tomorrow.

I am still not capable of putting more than a couple of hours at a stretch in at the bench I'm afraid. The Doc is pleased with my progress, has upped the painkillers slightly, and - within sensible limits - is allowing me to drive again. So there's improvement somewhere anyway!

Oh, if anyone can donate me any single mode fibre cable, OS1 or OS2 or anything with a 9/125 fibre core or finer, would be appreciated. Why? Well, check out this video of someone else's micro-fabricator: https://youtu.be/UvV2CH5il3Q which is using a fibre to spot-cure resin. Not the approach I wanted to take, but they get more views than me so I have to get with the program and be relevant :) The same arrangement will work just fine on the RepRapMicron.

I printed the Probe Flexure with a 0.1mm layer height on the Prusa XL and they came out really nicely. Worth doing in the future.

Still haven't etched the new probe. Thought I'd make a proper set of croc leads with a plug on, got croc clips, Du Pont connectors etc. and then cleverly put a socket on the leads instead of a plug. Arrgh!

I believe the USB microscope was resetting and misbehaving because everything was plugged into a USB 2.0 hub. I don;t think it could handle two high-res cameras with lights and an Arduino. Something gave. So I have replaced it with a USB 3.0 hub (any donations for my rapidly shrinking personal hardware fund to https://ko-fi.com/viksworkshop ...) and it seems to stay up for 5 mins without flashing the red light at me.

However, as is the way of things at the moment, I broke the flexure probe when fitting the microscope back on and not paying attention:

And so I have to make another one. I'll have to make a new tip as well because I really smacked the point into the slide hard and blunted it:

So that's another hold-up. 'Tis the season, apparently.
 

 

This time I'm making the very thing smear on the slide before I put it in the μRepRap. For reasons unknown, the microscope then crashed and flashed it's little LED at me. Reset everything, try again. Problem repeats. Unplug everything, reset everything, try again. Damn.

Okay, microscope is not playing today and prefers to flash status LEDs instead. I'll clean the slide with isopropyl alcohol and an air blast, put the microscope on charge to see if that helps, and try again tomorrow.

As the last attempt went poorly, I thought I'd take the opportunity to describe how I recover the slide. If you're using a new slide, the preparation is the same but without the initial peeling/scraping.

Required materials: Isopropyl alcohol or (acetone, MEK etc.), wipes (ideally lint-free), boxcutter, tweezers, air duster, adhesive aluminium tape, pointed probe, aluminium foil.

First, scrape up a corner of the old aluminium tape and use tweezers to pull it off together with the hardened UV resin on it. 

Then scrape the failed UV resin print off very thoroughly with a fresh boxcutter blade. Don't gouge in the point or use a nicked blade or you'll scratch the slide. Keep the edge flat.

Clean both sides of the slide with solvent and a wipe. Blow dry with air duster or clean shop air. 

Cut a square of adhesive aluminium tape, and stick it to one end of the slide. Burnish it down flat with a dry wipe. Pay particular attention to the edge closest to the centre of the slide. Wipe with solvent to remove fingerprints. 

Run the tip of a pointed probe along the edge of the tape. Push into the join, but not so firmly as to scratch the glass. The objective is to cause the edge of the tape to curl up slightly and present a barrier to UV resin that might otherwise encroach on the slide.

It's hard to catch it in the focal plane of the microscope, but you might be able to make out the raised edge above. It doesn't have to be particularly tidy, it's just a barrier.

The slide is then rinsed with solvent, dried with an air blast, and wrapped in aluminium foil until needed.

Well, that's how I do it at the moment. 

This didn't go to plan, but the failure was instructive. I started with drawing a 16x16 hollow square (black pixels on white background) then using this to create the GCODE:

../png_to_gcode.py 16x16_hollow_square.png -d 10 --safe-z 30 --dipify 100 -o test.gcode

The "dipify" tells the code to dip the point in the resin initially and every 100 points. That function does not currently do a UV exposure, so I'll have to remember to do that for now.

So a very small drop of resin (the probe is 0.3mm diameter for reference) is placed on the aluminium foil covered part of the slide near the edge. The droplet is ~1.7mm in diameter. Then it has to be spread out:

 

A little bit of Kapton tape folded flat over the end of a stick is used to push the droplet into a smear. This was my first mistake. I should have pulled the droplet away from the edge after pushing it forward. I've been away from this too long...

Time now for the probe to make contact. Note that there is a heck of a lot of surface tension around the probe/resin contact area. This is causing a lot of resin to accumulate on the probe. This is not optimal. If I had remembered to pull the droplet back after pushing it forward, the probe would only be entering a thin smear.

If you zoom in on the probe point here, you'll see the problem. The surface tension high up the point has caused a relatively large droplet to form, dangling from the point. This will make a large blob on contact, not a fine dot.

And everything after that point was a mess. So, I set the resin with UV to look at the mess (nothing of note), and cleaned the probe with IPA. I'll scrape the slide clean with a box cutter blade, then IPA, then a blast of compressed air, and remake the slide for another go. Hopefully tomorrow as I'm working today.