RepRap: Blog

I tried to create a single beam with a flexure joint in it as narrow as I could. We're looking at a flexure 20μm thick and a beam width of 60μm. The beam in the image is about 500μm long, but note that one end is severely dinged up. This happened during the washing process. These things are very delicate and very poorly attached to the slide. That goes double for long, thin bits. Hopefully I can string them together for improved stability. Also this one was only 20μm thick, and thicker is probably more durable - as long as you can get it to stay stuck to the slide!

This object is not attached to the glass, by the way. It came free during the very gentle washing/drying process. I can't see much until the prints are dry because they're too optically close to the surrounding resin/solvent and are basically invisible. I look for the distortions in the fluid surface, which the microscope overhead light brings out quite well. I know there's something there, but have no idea what it is until the solvent dries!

I had to bring print overlap up to 25% and "extrusion" width down to 7μm to make this work.  First layer is now 7μm and subsequent are 4μm. I'm printing at 120μm/s with 100μm/s bridging. Next step I suppose is to have two beams carrying a flexure between them...

I've dropped pre-built STL files for the UV fibre print head here https://www.printables.com/model/1871410-high-resolution-resin-print-head-for-reprapmicron

 

 

I've added all the stuff I used to generate the UV fibre prints (code and models for the fibre/LED interconnects) here:  https://github.com/VikOlliver/RepRapMicron/tree/main/UV_head

I'll get some instructions and assembly pictures together for the Wiki, but followers will have seen most of it in the blog. Shout up if you need anything to go to the top of the queue.

Gratuitous picture of a slide with the 500μm Benchy printed on it. Spot the Benchy:

 

Took me a few years, but here we are. This Benchy is 500x258x400μm and took the RepRapMicron PIKA V0.02  2hrs 41min 22sec to print in eSun Standard Resin. This was using the same 125/9 fibre head as before, but with the UV LED controlled by the GRBL Coolant Mist output:

Settings: 30μm/sec print speed, 25% speed first layer, 6μm first layer, 4μm layers, 2 perimeters, 2 top 3 bottom layers, 9μm print width,UV LED, and 56R 5W resistor. If you zoom in to the stern you can see the infill lines.

To rinse off excess resin I plcve the slide flat under the binocular microscope with a pad of tissue underneath. Then a 1ml hypodermic syringe and 0.5mm needle with about 0.6ml of isopropyl alcohol is dropped on and jetted at the print. This is gently air dried with a slow fan.

Yes, some detail is missing because the UV beam sets the resin for a considerable depth downward. This can be avoided by adding a UV dye to the resin, but I haven't done that. Have other plans. You can do it if you want, just use alcoholic turmeric extract. 

I'll take a pause from making lots of stuff to document everything and upload the PrusaSlicer filter, LED holder and so forth, have a coffee (https://ko-fi.com/viksworkshop) or mebbe something a bit stronger :)

I've managed to get something more plausible out of ordinary 3D Printer resin. The trick was to move faster with thicker layers. The print is a bit fuzzy because I'm not yet turning the UV LED off while moving. However, here is a cylinder notionally 200μm diameter and 178μm tall (my tallest structure yet):

 

There's probably the odd artefact from me turning the UV on and off manually at the start and end too. I'm running this with a 6μm first layer, 4μm subsequent layers, 2 perimeters, a print speed of 100μm/sec and a maximum travel speed of 250μm/sec - which it might be nice to increase because I can see hairy filaments where the resin has set in fast moves. First layer was at 30% speed btw.

Curiously, I'm not seeing the conical appearance of the Nail Art resin prints, which is good. Even more puzzling is the fact that those overshoot artefacts appeared in Diffraction Limited's  prints but not mine.

Anyhow, now I have something dialled in, I'll  try to get the LED turning on and off. Also might try a more mechanical part and another Benchy just for the lols.

The old light source was a bit hit and miss because its alignment with the fibre and the UV LED wasn't perfect. In fact shutting the workbench drawer could cause it to drift. I've purchased some 3W UV LED modules, and connected one of them up to a 5V power supply. With a modified adaptor, this now screws everything firmly together. Here's a low-light macro photo of the UV beam hitting a fluorescent translucent plastic rod:

There should be enough UV in that to cure the resin. The star-shaped LED base is an aluminium PCB with notches in, which takes M3 screws quite nicely:

The RAMPS board power outputs are at 12V, so I can't directly run this module off them. The UV LED in the stage runs at a much lower current, so I can get away with a small series resistor, but this thing is taking about a Watt. I'll have to wait until the stores open, then I'll go in search of a 5W 68R resistor to put in series. After that I'll be able to control the UV LED from GCODE.

I've been having little luck using the fibre process to create objects in 3D Printer Resin. At best I get a few fragments. They're either falling apart when I drop IPA on them, or not sticking to the slide surface properly. I very carefully ran a print at 1μm/sec with a 4μm first layer, and the Nail Art resin stuck while the 3DP resin didn't.

The object was a 100μm diameter minimug, with an attempt at two layers on the wall. Either the walls washed away completely or never got created. Here's the surviving base together with what PrusaSlicer thinks should be there: 

I'm using an improved fibre holder rather than the zip ties for added stability (photo below, on the left). 

Now, it could be that I'm attempting layers that are too thin, or just moving too fast for the resin to cure, but that's for further experimentation. The takeaway so far is that Nail Art produces something and 3DP resin produces nothing so my material choice going forward is clear.

They are important factors though. If I'm using enough UV but not using it right, I won't need to wire up this fearsome array of 3W UV LEDS:

 

I think that might contravene local directed energy weapons treaties...
 

I took a few measurements  off the micrographs of the most recent "Hello World" and got some data points. First, if I spread a thin film of Nail Art resin as thin as I can without leaving any wrinkles in the surface, the film is about 50μm thick. Any thinner and it starts to glob. I can spread such a film over at least 2mm x 3mm.

Shining UV from the 125/9 fibre a few microns above the film surface causes the resin to cure in the following pattern:

I am advancing the UV fibre along the surface at 2μm/sec. This gives some idea about how simple, flat structures such as folding frames may be designed. Obviously not very high resolution, but I suspect would be a fair bit faster than building something from single layers.

Unfortunately I am dragged away from the workshop once more and cannot conduct further tests on building layers with the fibre probe immersed in resin. My current theory is that it might be best to make the first layer several microns thick, which would effectively level the first layer. Then subsequent layers can be made a couple of microns or less thick.