RepRap: Blog

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.

Fired up the μRepRap after nigh on a month, and after damp weather following an air conditioning failure. Still in good alignment, so I had a go at a resin print.

As expected, the steeper angle on the probe used produced a bigger droplet size (hey, it was what I had fitted at the time). This may seem counter-intuitive, but I've seen this before and  I suspect that a thicker probe tip pulls more resin back due to capillary action. The deposited first layer was approximately 8-10μm thick. Here's a shot of me doing a few tests of micromugs:

The takeaways from that run are:

Raking light from the top camera (now angled in at 45 degrees or so) is causing reflections at the contact point between the resin and the slide. This was a suggestion from a fellow Fab Labber. This, together with the 4K microscope, allows coated probe contact to be visualised relatively easily compared to previous efforts.

The first layer appears to be substantially thicker than subsequent layers. This is a slight problem, because current slicers all let you set the thickness of the first layer by determining the standoff distance to the bed for the first layer, and with μRepRap, the layer always starts at zero. Prusaslicer does seem to have individually configurable layer heights though, so I'll have to play with that.

Eventually this is going to need custom software, but I currently don't have the resources to manage that and I'll have to fake it.

PS I'm feeling fine now, but have to go back in hospital in a week to be introduced to some tiny little cameras so they can figure out WTF is going on. I hope they're narrower in diameter than my microscopes!

Last few days have been interesting. RepRapMicron mailing list attempts resulted in my SMTP IP being blocked by  Google because I had the temerity to send out 20 emails at once. I'll add in rate limiting. I've put the code on github https://github.com/VikOlliver/listomail in case anyone who knows anything about writing mailing lists wants a laugh.

My time has, however, been limited for medical reasons which have left me a tad fuzzy-headed. These got even more fun when combined with floods that've cut off a lot of the local area (including the hospital) and me suddenly finding out that I'm quite allergic to a prescribed antibiotic while on the other side of said floodwater. Can breathe easily again and improving.