RepRap: Blog

Using OXX Cosmetics UV Gel Top Coat (acrylates copolymer, hydroxypropyl methacrylate, hydroxycyclohexyl phenyl ketone) I wiped off the applicator brush on the brim of the container and touched the slide. With Probe One I printed what I'm starting to think of as the "Test Loop." I printed a few other bits and pieces, interlocking 80μm and 30 μm test squares, blobs etc., and cured the whole thing. First for 30 seconds with the built-in LED, then for 200 seconds on a 4W UV LED lamp. No significant shrinkage was observed.

 

The Test Loop consists of a nominal 100μm diameter circle with a 100μm line sticking out of the side. That's pretty much what I got. Note that this was done with two perimeters and 5μm intervals between dots. I could easily get 30 dots between dipping Probe One in the reservoir.

Under the trinocular microscope at 100x I tried to lift some test pieces of print with a hypodermic needle tip. They were not wet, but they did not stay together when poked. They were stuck flat to the glass slide. Fragments attempted to straighten out, so they were not in gel form. I had been printing for over 3 hours at this point, so the Top Coat definitely cures after prolonged exposure.

I went to the (now hardened) reservoir blob and pried the edge of that up. The thin edges tore, so I started prying at it until I found a piece that could be considered strong enough to peel away from the glass slide in a sheet. The material was quite flexible and could be bent over on itself. It returned to its original shape quite positively if slowly when released.

I propped up a torn segment on a 0.7mm diameter pin to get a look at the thickness:

The minimal durable film thickness appears to be approximately 30μm. I tried to determine the thickness of the printed Test Loop. Fragments edge-on were beyond the resolution of my optics. This would put the printed layer at very roughly 10μm or less.

Slicing Problems

While the probe dipping code works, and the PrusaSlicer integration is fine, the slicer doesn't accept layer and line thickness proportions that can be used on a scale of 1mm = 1 micron. I'm going to have to add some scaling to do layers, or use the PNG to GCODE script to stack my own. Possibly both. Also having to specify the reservoir location in the script each time I slice is a pain in the butt. May need to change the reservoir location to something closer to XY=(0,0).

Conclusions

UV Nail Gel Top Coat is a viable material for resin printing tests in air, though repeatable layering is yet to be accomplished.

With UV resin there seems little point in trying to print details much finer than 40μm at this stage as they are not robust enough to survive being detached from the glass slide with the equipment I have.

With 30μm voxels, it would take approximately 1mm^2 to make a complementary flexure that could move +/- 40μm. That would take several hours to print each layer at current speed, though that could be improved as micron precision is not required.

Probe One is a little too coarse for optimal resolution given 30μm voxels. 

Given a maximal thickness of the printed layer of 10μm and a minimal viable mechanical thickness, any printed object needs to be at least 3-4 layers thick to survive manipulation.

Before starting the "Top Coat" nail resin tests, I thought I'd check the state of Probe One (acid/salt etch on Nichrome) to see if it was still in good shape after being used for all experiments since the 17th October. Well, yes. 

I haven't been treating it particularly gently. I have been cleaning it with an isopropyl alcohol spray. But then I've been gently wiping it dry with the corner of a Sorbent white tissue. It's stood up better than anticipated, and the surface still seems to have pores in it.

That XY Table I said "Don't print this model, it's only a mockup"? Well, I had the model and there was a printer next to me. It kinda happened. In my defence I only printed it at 60% scale.

 

If you're also going to not print it, I warn you that my flexures were just eyeballed for the sketch and are too thick causing unwanted resistance/rotation. Also it needs a base of some kind (preferably with diagonal bracing) to stop the bent flexures digging into the floor. Other than that it moves surprisingly well, no sagging and the centre stays level when you move it about.

As I say, needs connections and mounts for axis drivers. But, uh, wow. Useful exercise. I'll keep it around to model in OpenSCAD if nobody else does it hint.

Now, stop playing with it Vik, and get on with the resin experiments. 

I've had this buzzing around my head for a bit. By clever arrangement of the flexures, I think it might be possible to print-in-place the XY Table. So I roughly (really roughly) drew this up in Tinkercad, which is really quite good for 3D sketches:

The green bit is the stage, yellow bits are flexures, red bits structural beams, and the grey bits will be hollow boxes but I've made them see-through so you can see the guts. The outer hollow box is the frame.

If you fancy tinkering yourself or looking at a 3D view, I've stuck it on the Fab Lab's public area: 

https://www.tinkercad.com/things/dTJWUZJloZ0-reprapmicron-xy-flexure-mockup 

Attaching the X & Y Axis Drivers is left as an interesting exercise to the enthusiast. Again, this is just a rough mockup of an idea. It's not meant to be a real printable thing. Do feel free to fix that... 

Got enough stuff up and running. Bodged a 12V laptop power supply into the microscope. New USB for the USB microscopes. I got some of the "OXX Cosmetics Cherry UV Gel, Nail Polish, Jelly Finish." Label states ingredients as "Acrylates Copolymer, Hydroxypropyl Methacrylate, Hydroxycyclohexyl Phenyl Ketone, Silica, CI 15850, CI 19140"

This appears to have some kind of dispersion in it (the silica?), but the particle size is not significant for the resolution of the μRepRap. It is very thick, and wants to stay in large blobs. Attempts to make small dots resulted in 50μm-80μm features as per lower left corner of the structure. The approach of using "dipify" software to make a pre-determined shape was abandoned, and a 500μm square manually created by dragging out the initial contact point, recharging the tip for the next side, dragging that out etc. This was Probe One, which is rather blunt, so perhaps different results may come from finer probes.

500μm Square, "Jelly" nail resin

Side view using lower quality microscope

 

 

Closeup using trinocular microscope

An attempt was made to create some kind of tail to hang on to the finished item. The resin was first cured using the built in μRepRap UV LED for 30s, transferred to a 4W UV LED for 180s, tested, then exposed for 8 minutes.

Adhesion to the glass surface was very good. The bulk of the large blob had enough strength to stay intact in the centre, but cracked when removal was attempted. The underside appeared to be of a similar consistency to the top surface. There was a notable lack of the clear, uncured fluid seen around attempts at curing 3D printer resins.

The strength of the resin was insufficient for the edges to be cleanly lifted from the slide though did have cohesive properties and hints of a stable layer were visible. The relatively thin single layer of the experimental square did not have enough strength to survive attempts to separate it from the slide resulting in the following mess:

Square destroyed by attempts to lift it

 

The "Jelly" nail resin did cure, and was easy to see. It was not immediately possible to create fine structures, and the results - with single layers anyway - were of low strength. Making this work with a finer probe might be challenging, and require multiple passes. I'll call this as being more suitable than 3D printer resin but not ideal. The "Top Coat" is supposed to be thinner and harder, but with poorer adhesion and harder to see. That'll be next, but that's not the only work on right now.
 

I haven't been able to use the workshop since the storm. It looks like one phase overvolted significantly. The printers still seem to work - they were turned off - but I have lost the microscope power supply, bench USB supplies (several), and all the charger units for my DeWalt power tools which are now useless as they're older XRP models. The RepRapMicron is on a 25 year old "survivor bias" PSU built like a tank, and that still works.  A few other odds and sods don't.

Most annoying. Still, the things that were running on the backup inverter have survived. I still have my laptop and screens. Obviously I have a lot of fixing to do. We'll see what we can get running.

A kindly nail artist suggested that I try this OXX Top Coat obtained from a convenient Kmart on my travels:

We survived Storm 1. Some property damage, power out for 10,000 homes now down to 2,500 but we're one of 'em. I have essential power, but none in the workshop. Powerco doing their best with my driveway and paddock looking like a construction hire company lot.

Should have that sorted soonish - just in time for Storm 2. A "Red Warning" with threat to life in about 18hrs. I'll keep the batteries topped up...

Then sadly I have family business to attend to in person. So if I drop off the radar next week I'm just flying low.

Here's the hard working Powerco Boys getting ready for a pole dance.

 

While waiting for nail art supplies I thought I'd try out metal foil. I have some gold-ish "Dutch Leaf" which I placed gently on top of a few resin dots and held over the UV lamp. I gave it 4 minutes and peeled off the foil.Fragments ended up all over the silide, the tools, me, the microscope, and the bench. Attempts to remove fragments guilded everything.

Examination of the remains showed 0.1-0.2mm dots of resin on the foil. It prefers to stick to the foil, not the glass. Observe the circular spot centre left frame between the two horizontal thin lines:

 

This is resin. It has cured, but is exceedingly thin and fragile.

I would love to continue, but we have a severe storm and the power is out. House is shaking like a caffeine addict, debris pinging off the outside walls everywhere. Backup power does not extend to the workshop, and I wouldn't use it if it did.

The CO2 container helped, but did not preserve the fine detail - that stayed gooey. Not good enough, but will repeat the experiment in case it was a fluke and give more than 4 minutes curing time. Yes, that's short for curing normal prints but its not as if the UV has to penetrate very deeply.

Perhaps there is already significant oxygen dissolved in the resin from exposure to air during deposition? The larger blobs were also distinctly wet underneath, but not as bad as earlier attempts. So I put the sample in the air fryer at 90C for 15 mins. Still not set, let's give it another hour...

Maybe some kind of cover to avoid flying fried chicken particles might be a good idea next time. Anyway, some more resin cured, and there are small chunks of cured resin in the print, but the fine details are not preserved.

So what thickness of printer resin do I need before it'll cure? Well, I have the blobs, so I broke one apart at the thinnest identifiable solid area and set a fragment of it on edge:

This also shows my limits for manual manipulation. The answer appears to be about 25μm. As I'm depositing dots smaller than 10μm, no wonder I'm having poor results. It also means that unmodified printer resin is not going to be useful with fine probes, and any objects I deposit need that as their minimum thickness. Damn. Something else to test as well.

There are additives that I can use, which are in common use in things like UV nail varnish and fibreglass resin hardener. Plenty of things to try out. I might try putting a few dots down, leaving them exposed to air for increasing intervals, cover them with gold leaf to exclude air and try hardening that. 

Mechanically, the resin is relatively inflexible. From just poking at it with a probe though it feels like I could make some kind of flexure out of it. No idea how it'll stand up to repeated stressing. Also there are more flexible UV resins available for DLP printers, and standard/flexible resins can be blended to get the desired rigidity.

I think I may have to lay hold of some "No Wipe" UV nail varnish. That has an oxygen inhibitor in it so that a thin layer can cure in air - and I can buy 15ml quantities. Hmm, I wonder if I can get some in translucent colours to make imaging easier? Plus I can do up my nails...