RepRap: Blog

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.

Soooo, turns out I needed quite a lot more of the blocker pills once I got up and about, and something else cropped up during a scan. Damn. I think I'm back on top of it though. Can walk with stick, even allowed to drive the 10 mins to town (but no further). So back at the workbench, which currently looks like this:

 

I'm having too may problems with artefacts from slicers when trying to deposit objects. Anyone want to help write a custom slicer?

[crickets] 

In that case, to make progress, I'm going to use the png_to_gcode.py script to make something simple and repeatable, where I can alter one variable at a time. That script takes a black and white pixel image and plots it as dots of resin with a spacing and height of the user's choice. So far I've only really used it for etching in Sharpie marker.

The plan:

Determine voxel spacing needed to deposit a square that clearly isn't blobbing in at the corners. How many microns between points? Is one row of points enough for a reliable line?

Establish the height of the square's sides.

Deposit a second layer. Determine the height of that.

Repeat, third layer.

Now this all sounds nice and straightforward, but I'll be really lucky to get this done with three resets or less. I have to clean/swap probes before measuring the height of something for a start.

How far have I got? Well, I have moved the RepRapMicron onto a sturdy bench that is separate from my keyboard, so that I can operate the machine without vibrating things. I've shortened the microscope pole to lower vibrations off that, and I've prepped a slide with an aluminium reservoir (I'm using adhesive aluminium tape). I have a 16x16 PNG of a square to start with.

But I have to meet a good friend in an hour, so I can't start now. Hasta Mañana, Amigos.

The FPath Project is an R+D effort to follow the Feynman Path to Nanotechnology - the use of tools to build smaller tools which then build smaller tools and so on. The ideal situation would be the eventual development of kits of tools and techniques applicable to various scales (sub-millimeter, micron etc). 

In order to bias the direction of the FPath Project experiments towards this goal, a series of challenges has now been created - each of which solves a useful problem. 

http://www.ofitselfso.com/FPath/SubMillimeterChallenges.php 

The FPath Project will attempt to complete each of these challenges - but they are generally open to others. If you complete a challenge (or even make a valiant attempt) I am happy to post a link to your solution on the the Results Page.

New Challenges will be added in the future and suggestions are appreciated.  

Labels: Additive Manufacturing, Feynman Path, Nanotechnology

I can now sit at the desk again for a bit, and slide things around the bench. Tremor from blocker pills is fading, and I can manipulate tiny things. So I've shuffled the μRepRap under the binocular microscope:

 

This gives me an enormously better view. Erm, 3 wee issues:

1.    While binocular vision is very nice, I can't share it on the blog.

2.    When looking into the binocular microscope, I can't operate the CNC jog controls.

3.    I can't bend over to look through the eyepieces for very long right now.

4.    It does rather get in the way, doesn't it? 

 

I'm collecting ideas for when I'm declared fit again:

Cheat like hell to get a useful micron-sized tool. 

Etch a pattern into some Sharpie or other masking material, then drop resin on top, then expose the resin through the etched Sharpie mask.

Try the old "write on a grain of rice" trick.

Nail some CNC joystick control software that allows constant acceleration with an analogue stick.

When removing the previous probe, the one with the touch indicator on it, I realised I didn't have anywhere to put it! So, I've uploaded a newer version that has a tip cover that can be attached using a screw.

I'm going to have to construct some kind of enclosure for the μRepRap, as I'm having problems with sunlight prematurely curing the resin during a print. The tip on the probe in the picture above is in fact caked solid.

Progress too on the RepRapMicron mailing list software, "listomail", which now supports the redistribution of file attachments to the mailing list. I've yet to add autoreply detection, and the IMAP handling relies on tickling the IMAP timeout with NOOPs too much, but I think the list server script is now sufficiently reliable for regular use. So pipe up if you want to join the email list.