RepRap: Blog

Happy New Year!

The hand has healed up enough to make more slides, so I printed all the ideas I had kicking around while convalescing. I tried a few 200μm diameter micromugs, which ended up being dog bowls again, and a chain of hinged squares to test multiple folding. I'll cover that in a later post when I've origami'd it.

But the main push was to try and print a pyramid, on the grounds that they're infamous for standing up. Mine was 400μm on each of its three sides, and 300μm tall, making it the tallest and largest thing I've tried to print.

Of course, it didn't go as expected. It looks like it's spent 10,000 years in a rough desert and learned bad things from a ziggurat:

It didn't help that I probably started the probe a bit too low either. My guess is I need to get the layer size (2.5μm) down even further to make sure there's enough resin in the middle of it, maybe adjust the print width a little lower too. However, it did print all the way up even if it did sag like a poorly-baked cake! Where the print is sliced a little denser at the top and the corners you can see some facets trying very hard to happen.

The UV cured the resin from underneath too, so that answers whether the underslung tiny LED can cure relatively thick layers of resin.

Other good news, the printer stayed together throughout the entire process, and the resin was in the reservoir was still perfectly good after all the exposure to air and scattered UV. I should point out too that this was printed using short segments rather than dots of resin. That is significantly quicker to do. It would be interesting to compare the dot-by-dot approach for quality at some stage.

Why is it dark grey? It isn't. That's a refraction of the black microscope stand underneath. Doesn't it just highlight all the defects beautifully? The resin is actually quite dense and optically good, which is why I think I need to just make the layer spacing a bit thinner. Could probably print simple optics. I'll finish off with a shot taken straight down onto the frosted glass surface:

 

Working on improving the photography. The trick with propping things up on lead bullets only gives me a couple of directions of viewing, so I've designed a gimbal rig. With this I can turn the microscope slide any which way under the binocular microscope. Getting good pictures is important because saying "I am creating tiny transparent things that only I can see" is a good way of getting an express ticket to the Funny Farm. Here's a good angle of the folded squares:

 

It has two sets of pivots, and the base can be rotated to give a third degree of freedom. This is what the contraption looks like:

 

If you want to build one I've put the STL model and source here: https://www.printables.com/model/1534011-microscope-slide-rotating-gimbal-mount

Back again, been doing a bit of organization behind the scenes. The hand is still a bit wobbly so I increased the size of the hinged squares to 0.8mm on a side and two print lines thick to give me a fighting chance.

The sides are 30 or so layers thick and two print lines wide. Line thickness is dependent on direction of travel of the angled probe, so I'll make one with a vertical tip later.

The lower square is filled in with 2 solid layers. I tried depositing unset resin on the hinges, but didn't get enough on and added some manually with a hypodermic afterwards.

After gently teasing the hollow square off the slide manually under the binocular microscope, I folded it up 90 degrees, and held it in place with a "finger" - the little hinges are capable of pushing the 15g weight aside, so I'll have to make a heavier one:

Then I added resin to the hinges and cured it all with a UV lamp. The square stayed vertical, so I threaded one of my fine greying hairs through it for the top photo.

This is the current microphotography rig:

I have a new ring light that allows me to use the crappy 0.6 Mpixel microscope imager. A new 8 Mpixel one is on order. I have been planning a better gimbal rig for orienting the slides. I hope to get μRepRap under the rig too once I have joystick control software, which will allow more delicate manipulation of finer prints and better imagery. 

I have now posted the results of FPath Experiment 011 which is part of the FPath project. This is not an actual experiment per-se, rather, it is documentation of the image recognition and Graphical Stigmergy techniques applied in Experiment 010,

Experiment 010 used an interesting image recognition technique in order to automate the movement of a probe at the sub-millimeter level. The major benefit of this technique is that it is fast enough to keep up with a sequence of 640x480 images arriving at a 30 fps frame rate. 

Also, which may be of some interest, is a discussion of the mechanics of the Graphical Stigmergy algorithm. This discussion shows how complex emergent behaviors can be obtained from combination of relatively simple actions and the modification of the environment to send signals.

I just thought that some of you might be interested in how all this is done. The video explains all: https://youtu.be/be725uWk4c8

The image below shows a frame from the video - Ok, I know, it isn't the most sophisticated graphics you've ever seen. (click on the image to enlarge, watch the video for context) 

 

Labels: FPath, Graphical Stigmergy, Image Recognition, Sub-millimeter Control

One idea for fabricating structures with RepRapMicron is to print them flat with hinges, and fold them up into place. I thought I'd try it out now I can print ... things using 2.5μm layers. So I took those badly printed linked 400μm squares from the first image and just gave it a go manually under the microscope. The result didn't end up like origami, more like a crumpled tissue, but it demonstrates the principle and I learned a lot about how I'm going to need to do it in an automated way:

 

I didn't mind sacrificing the awful print, which is just as well as I ended up breaking or damaging both hinges. The point I used to deposit resin in the joint to lock it was way too large. I needed a static prop to lean things on, so I put a hypodermic in a clothes peg. Even so I missed my 90 degree target by a bit - need longer hinges.. Curing the resin was done with a hand-held lamp. I tore parts some, so manipulation tabs would be a good idea.

Might make a few changes and try for a full cube, simultaneously improving print quality. Will need to make a slightly finer print probe at some point, and possibly a manual probe for putting resin on joints. Also, drinking less coffee may help.

I managed to make a taller object. Kinda. I've been drawing short segments rather than dots because it is significantly faster, but it does not seem to be accurate enough for fine work. Maybe with a finer probe?

Anyway, it looked plausible from the top view. This is 400μm diameter and allegedly 125μm tall. The purple colour is because I put Vivid marker under the resin reservoir:

Slightly blobby, but has obviously slumped when viewed from the side:

The lowest part on the perimeter looks to be about 2/3 the way up, so my guess is I got to 90-100μm before it all flopped over. That's not too bad. The wall of the cylinder is double thickness BTW Will try again with clear resin and probably stop at 100μm so we have something cool to look at.

Also tried printing two 400μm squares with a 100μm double hinge between them. Haven't poked at it yet. Note that the left square is filled, the right one is hollow:

 

Looks to be a little uneven but I don't think I was running the probe out of resin enough before removing it and things got messy.
 

Remember that unsuccessful attempt at a micromug? Well, I wanted to reuse the slide and set about cleaning it off. I noticed that I had not cured the resin in the reservoir, and it had flowed around - but not into - the micromug. I thought it might be messy to clean off the resin, now two or three days old, so I decided to try to cure it with a UV lamp. It cured, and I started to peel it off under the binocular microscope to make sure the slide was clean.

To my immense surprise, I was able to peel the object embedded in the flowed resin off intact! Closer observation revealed the bottom of the micromug - approximately 12μm thick - also remained intact. This suggests a way in which thin printed objects can be removed from the slide. Here is the micromug embedded in a thin resin sheet, lifted and placed almost on top of a 0.5mm hypodermic tip:

 

This is the first time I have successfully separated an object from the print bed. Granted, it was an awful print, but it has still served a useful purpose.

[UPDATE]

Here's another truncated micromug with a bit of Vivid marker in it. The outer 40μm rim is definitely solid enough to be manipulated with a hypodermic point, and you can clearly see not just the 3D shape of it, but the intact base to the micromug.

By the way, I cleaned Probe 9 off by soaking it in a 0.40S&W case full acetone and scrubbing it with a cotton bud. It seems to have survived this treatment. We shall see. Darn thing could be tougher than originally envisaged.

Looks like (on a sample of 2) folding the edge of the foil reservoir is a good idea after all. I think the UV is reflecting inside the solidified resin that creeps over the edge, which then sets everything solid for a millimetre or so. Unfortunately that was where Probe 9 was. It's got a bit of solidified resin on it:

I also accidentally drilled into the foil, which creates a hole. Which lets in the UV, and that sets too, encapsulating the probe. It got pulled out leaving a crater. The muck on the probe, and the resin build-up at the edge conspired to produce a wave of semi-set resin at the edge of the foil, which the probe duly swept into the print attempt, totally ruining it.

I don't know if the Vivid marker had anything to do with it or it was just attached resin, but one or the other insulated the tip of the probe. So when I tried again, with the next Z Touch the probe didn't stop and pile-drived into the slide.

I have straightened it, and will try soaking it in acetone to revive it. I have low hopes of success, and see more etching in my future.