RepRap: Blog

I now have a couple of pretty identical tips:

Probe #17 received the second pass treatment (top) with probe #18 for comparison. Might need to tweak the second pass GCODE to take a little more off, but we'll see which one works best first.

I've fitted Probe #18 to a flexure tip holder, and Probe #17 to a holder that has been extended so that I can get the microscope angled more vertically over the probe:

 I'll try that one when the glue has set and I've put the Z Axis back on the PIKA.

I wanted to get the tip right, and the tips I was making just weren't ogival enough. For those going "Wut?" an ogive is the shape of a pointed gothic arch. I made another probe tip because I wasn't sure how this would play out. After the automated two-pass etching process (without roughening) it looked like this:

 

 It's too aggressive. It needs to be less pointy.

It might be fine for depositing teeny little dots, but what we're trying to do is lay down 20μm-30μm lines and build something relatively solid. The catch is that we need to do that without flooding the nascent part with a torrent of resin. The ogival point I created for Probe 10 seemed to do that well. 

I ran the second half of the automated etching GCODE that basically tried to etch off the last 2μm at a time. I noticed that it etched off roughly 8μm at each dip, so a lot of dipping time was wasted. I wrote a second piece of GCODE that dipped 5μm at a time and ran that. I took off approximately 110μm  of the point and it looked like:

Now this is much more like the desired ogival outline, and the area above the tip is roughened so it should hang on to a layer of resin by capillary action. I'll mount this one in a contact flexure and we'll try it out. [Edit: Turns out I put my monitor on top of the last printed flexure so will have to print another]

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.