RepRap: Blog

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. 

I've got a process sorted for making thick 2D objects like Hello, World and possibly some structural items. I recreated the HW by the following process:

Text is created from an SVG and converted with jscut.org using a speed of 1000mm/min, 10mm tool diameter, outside cut, cutting 1mm in 10 passes. This effectively goes over the text 10 times while only moving the tool head a micron. I do not claim these settings to be optimal but they are repeatable.

Stick a very small piece of tape on the opposite side of the slide. This denotes where your part will be and makes it a helluva lot easier to find!

On the "right" side of the slide, smear a very small quantity of Nail Art resin (not doing well with 3DP resin yet) and use a manual probe to make sure it covers the taped area smoothly with no bubbles.

Set the μRepRap up, position the fibre as close as you can get to the thin film. Load "Hello World" GCODE. Hit 'Run" and turn the UV on. Wait until it finishes and immediately flip the UV off. In this example I did not flip it off, but moved the tool to (0,0) and then rapidly to (-50,50) before turning the laser off just to see what happened.

The result:

Looking from the side you can get an idea of the thickness. It is interesting to note what happened with the manual move of the UV beam (tail, bottom left). Apologies for lousy photography:

The result is table, can detach from the slide, and appears to be moderately flexible as per this animation. Do bear in mind that when I poke it with a needle it's the equivalent of poking a macro-sized object with an aircraft carrier:

 Obviously, this affects plans for making small tools and mechanisms...

 

Oh yes. Barely recognisable, resting on the sea bed at nearly 3 kilometres down...

Well, maybe not, but if you squint it looks like a Benchy sure enough. The wee beast was sliced on PrusaSlicer, and the GCODE slightly filtered to to 650μm long (1/100th scale) without extrusion and other GCODE commands that confuse the heck out of GRBL.

Next step was to load it all into CNCjs and fire up a couple of microscope views. Then the end of the 125/9 fibre was touched off on the glass slide just by eye, and raised I think 30μm:

 

Then a drop of nail art resin was deliberately dropped onto the fibre tip. The GCODE was run and the UV source manually turned on. The model tool 13hrs to print with 2μm slicing and 10μm/sec print speed. As non-printing movement speed was far, far higher, it was not necessary to switch off the UV source.

So controlling the UV with GRBL is probably a good idea - I missed the end of the print by 5 mins and kinda irradiated it a bit. Also the UV blasts through already printed parts and sets all the resin underneath. Diffraction Limited uses turmeric extract to fix that. I might do that, or use a UV-resistant marker pen ink.

I think the speed can be cranked up, and the layers made a little thicker. This'll speed the print. Ultimately and improved UV source and greater speed will help.

But overall the process is quite fast, quite easy to set up, and will allow me to print some serious parts even without the above modifications. 

I'll talk about the philosophy of moving to fibre/UV another time, it's kinda deep. I'll leave you with a picture of Benchy in progress. It's not easy, but you can just see bits of it inside the resin droplet just under the centre of the white fibre sheath.

 

Cut to the chase. Have this wondrous bit of psychedelia:

The writing is 250μm across. That's meant to be a 100μm square at the bottom, but obviously I need to work on something. The lines are approximately 10μm thick. I think they're about 50μm high but don't quote me.

How? You may ask. Well Diffraction Limited did this video where they used their very high tech 3D manipulator to 3D print using a 4μm optical fibre and a UV laser. I don't have that stuff. But thanks to a helpful donation to my Ko-fi account (hint), I could get some cheap 9μm fibre and I do have a 1W UV LED. Now you'd normally use some kind of fancy coupler to connect the fibre to the light source. I, uh:

 Yah. The other end of the fibre, obviously needs a high precision connection to the μRepRap which..

..kind of degenerated into a couple of zip ties. None the less, if I smeared out a layer of resin, set the movement speed to 1 micron per second, and did about 10 circuits , I could set up 50μm or so of resin in a 100μm diameter cylinder:

 So there's my 100 micron minimug. Got to run. Hope you enjoyed.