RepRap: Blog

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...

I made a wee box to hold a UV light and some CO2. There's a bit of tape at the bottom to hold the slide in place, and a hole in the lid for me to gently squirt CO2 into from the family Sodastream. Being dense, the CO2 should accumulate at the bottom of the container.

The test article for the cure is an attempt at printing a flexure. Unfortunately the dot spacing was finer than I thought I'd get away with using Probe One, so the lines don't join up. I spaced the proping points at 10μm and will use a finer 5μm resolution on the next attempt. I can probably do more than 15 dots in a row too.

 

 [Image above modified with "pop" filter]

The flexure frame is about 500μm across. I deliberately blobbed the bottom of it unto a puddle of resin to give it a sort of handle. Dragging a line from the puddle to the object makes too large a blob and wipes out the object. Must drag from object to puddle next time.

Not going to be a pefect result, but it'll test the process. We'll see how it goes. 

The dipify_gcode.py script seems to be functional again. Needs a couple of tweaks, but I printed this using it with 8μm pixel spacing and Probe One:

 

The slicer is adding a few clever bits for extrusion that I don't know how to turn off, but it plots one layer on top of another now. Just need to add something to flash the UV LED to cure the resin.

About that resin... Funny thing about 3D printer resin is that it doesn't cure well in the presence of oxygen. Not a problem in a standard DLP printer, but obviously μRepRap has issues there.

Now you can cook the sample at 90C to encourage it after printing, or use a shielding gas - CO2 is fine.

But I wondered if we can use this to our advantage. If we deliberately cure resin in air it goes semi-solid and washes off with IPA. Thought: Cure support material in air, and what we want to be solid resin under CO2...

 

We knew there was something up with the Y axis. Here's Exhibit A in centre frame:

That little hook-like protuberance is what holds the anti-backlash bands on. Those lugs are optimistically thin, and under load seem to bend out. I've strengthened them and added some clearance inside the frame in case they bend again anyway. Made a bit more room in there for the bands too.

While I had to take the damn thing apart I took the opportunity to replace the Y Flexure with a solid beam rather than the wibbly flexible thing that V0.04 needed. Testing that before Githubbing it.

There's more stuff to come on problems with curing UV resin properly, but we'll get there after I've done a few more tests on it.

The colour scheme is definitely taking on a festive air. 

The LCD-as-a-backlight trick doesn't help image structures around 200μm across with the camera. It does help me see and find them on the slide, but that's a visual trick requiring binocular vision - your eye notices the discrepancies in the left and right images.

I tried to create the shape using the GCODE "dipify" code that turns GCODE slicer output into dots, but that went poorly because I've stuffed up the python script in a really weird way that'll take a bit of investigating.

But I did manage to get the lighting angle right in the cheap scope, so here's what happened:

 

Plotted in resin at 10μm/step using Probe One, 16 dots before recharging the probe, then cured under UV. As you can see, quite the distortion under deposition and curing though Probe One is a durable, blunt-ish probe and I might well do better with something more pointy if only I hadn't rammed it into the slide. I might be able to do better line integrity if I decreased the distance between plots and kept the object the same size.

However, that image is definitely resembling the test loop in promising ways. Being able to image something at last by waving lights around the microscope stage is a big deal. Now I can do that I have four things that need doing and I'm undecided about the order:

• Fix the "dipify" GCODE script
• Print a foldable or flexing structure
• Try to deposit actual layers
• Try to attach a printed object to a wire or probe tip for handling

Feedback welcomed. 

Just for giggles I worked out that assuming the hole (~70μm diameter) was the flagpole hole on a Benchy, and I can do layers, overhangs etc. (bridging in just resin is unlikely at this stage, but there are tricks) we'd be looking at a 3D Benchy roughly 1.6mm long. If I cheated and filled in that and the funnel hole like every other beggar printing tiny Benchies, we'd be looking at a 0.5mm long Benchy, or possibly a 300μm Benchy-Shaped Object. Of course, this is all pure speculation because I haven't deposited an actual shape in layers and the whole thing may just melt into a puddle.

I laboriously peeled off a large sheet of polarised film from an old LCD, crossed the polarisers under the microscope with a random resin sprinkle between, and ... it didn't help worth a damn.

Then I used my cellphone as a polarised light source. That didn't help with polarised viewing but I noticed I could see the grid pattern of the screen. This is because the little dots of resin act like lenses, and bring the LCD pixels, which are out of the depth of field, back into focus. This image is approximately 1mm wide:

Of course, I have to take the picture with the crappy imager because my cellphone is under the microscope, but we can see a number of little grids where the resin dots are. The smallest seems to be around 50μm, but as I change the focus on the microscope, different sized dots come in and out of view as their intrinsic focal length is different depending on the diameter and thickness of the dot:

The smallest dots visible seem to be in the order of 50μm. I'll print more accurate structures, find another cellphone with a decent resolution screen, and check back later.

You may remember that Probe One had a somewhat spongy appearance, and I wondered if it would absorb resin. I fitted it, stuck it in a blob, and yes it does. Whether this is a good or bad thing remains to be fully explored.

 

Here you can see the dark line of the resin creeping up the probe, above the meniscus of the resin. A reminder that Probe One had a rounded tip rather than a sharp point.

I had updated the png_to_gcode.py script to "dipify" the probe and created an 8x8 pixel hollow square. This is not yet in Github but will be updated after a bit more testing.

After manually aligning the probe with the Stage using Sharpie, determining the location of the resin reservoir (an unshielded smear)

I created several plots for the 8x8 pixel square:

• Spacing 30μm with a dip every 5 dots.
• Spacing 15μm with a dip every 8 dots.
• Spacing 10μm with a dip every 12 dots.

Then, picking points over a ~500μm distance of the reservoir I plotted the squares - without adjusting Z height. All the prints were only just visible and were at the limits of resolution of the guide microscope due to being small and transparent. It was not possible to photograph the results with the binocular microscope.

The 30μm square showed distinct dots of approximately equal size. They appeared even, though when moved to the binocular microscope after UV curing one corner had significantly drifted.

The 15μm square showed the occasional dots attempting to merge, but all dots were deposited. The consistency is TBD because of the viewing issue.

The 10μm square appeared to show contiguous lines of resin  with the dot placement barely discernible and possibly part of my imagination. One corner blobbed over into the interior a bit, possibly due to it being the first impact point from a dip. It may be necessary to sacrifice the first dot after each dip to ensure consistency.

The results were visible in the binocular microscope, probably due to the optical effects of viewing slightly different images with both eyes. This means they are not readily photographed, and even with AF Lock the cellphone camera would not resolve the image. Nor would my ancient cheap-arse microscope imager.  I transitioned to the bench microscope. Unfortunately the more powerful lenses have suffered over the years, and I could not resolve the image very well. Are are the original and enhanced shots, the smallest square is lower centre:

 

I attempted to use an ethanol-based safranin stain (which seems to stain every damn thing in the workshop if let loose) to improve contrast but sadly this destroyed the sample. I suspect it rinsed off, even though I used minimal water. I'll try a few different ways of resolving resin features and try again.

It is essential that the results be successfully imaged so that I can determine how many dots can be deposited consecutively, and their quality/height. This will matter even more as we move into 3D and microscopic mechanisms.

Now the probe is reasonably consistent over 200μm or so, I thought I'd have a stab at the 300μm test image with 15μm spacing. Here's how it came out:

The consistency of the dots is much improved, and we can start to see other variations in a useful way. There were other attempts, of course. Some of the test prints did not show white, photographable dots because they were only partially embedding into the Sharpie layer!

I did a series of dots at decreasing height of 1μm by the way, and the Sharpie layer is about 4μm thick. 

So looking at that with a calibrated MkI Eyeball I'd say our current hardware limitations are an accuracy of about 10μm on the XY plane, similar backlash, and within a couple of microns of height over 300μm of planar movement. So let's work within those restrictions for now.

The latest test results on height showed that the levelling bodge was likely stable overnight. I retested it, tested it in the same place, moved Y +100μm, tested that again, and finally did a test of Y +500μm. Results show some linear displacement on X, but I'm not going to fiddle with that for now.

Next steps, put "dipify" code into the PNG plotting script, put Probe One in the machine, and test some resin deposition. Of course, something else will come up...

Got it down to 1 μm in 270μm!

As per previous testing the probe wasn't staying at a consistent height, but the change seemed to be linear. So I tried propping up one side of the slide by sticking layers of that well-known precision shim material, duct tape. Yes, that's right. If it's good enough for bodging Apollo 13, it's good enough for me.

The tape was placed on the edge of the underside of the slide in stacked ~6mm strips. Each strip is approximately 0.35mm thick. The slide was covered with burnished ~10μm kitchen foil, burnished flat, adhered with UV resin that was pressed before curing. I used "Probe Zero" - the robust hypodermic tip. The results:

The Z axis values are reversed because I'm lazy and couldn't be bothered typing all the minus signs. The red and blue lines here show what happens with 3 layers of tape. The lines cross because I did the test with the tape on the -X and +X sides. As expected, the slope is fairly similar but reversed.

The yellow line is with one layer of tape on -X, and the green two layers on -X. As can be seen, one is too little (1:127), two is too much (1:128) because the slope changes somewhere between the two which would put the elevation needed at ~0.5mm. The previous round of testing indicated an error in the order of 75:1. I was unable to split a length of duct tape, but I strongly suspect one and a half layers would have been just about perfect. Total measurement error appears to be about 2μm judging from the delta between readings.

That represents roughly 13μm height gain/loss per millimetre of travel, which is probably enough for resin deposition of small objects. This only tests the X axis, but we know there is a deviation on the Y axis as well which is yet to be tested for.

My conclusion here was that designing a Stage with some kind of levelling in would take out a lot of the height variations and should probably be done before further resin tests to avoid probe damage. This will also facilitate Y testing. So another simple bodge: Stick split washers under the Stage mounting screws:

The maroon line here is the end result of the fiddling with the mounting screws after five tweaking sessions. Range of motion was 2400μm (2.4mm) and the final deviation was 8.7μm. This equates to the height being 1μm out in 277μm of movement on the X axis, so good enough for me to make things about 500μm (0.5mm) across. That's the approximate equivalent of the width of a human hair over an inch in old money.

Now the Y axis... 

Probe One (the acid etched stainless steel one here) was successfully mounted using the mounting jig and put in a nice, protective box until I'm ready to proceed. There's definitely a knack to it, and the jig definitely helps.

I'm going to get some polarized filters and test them on the binocular microscope first, just to see if it makes it easier to see the tiny little resin dots. There was an article on Hackaday about that a day or so ago, though that was about reducing reflections and I kinda want to increase the reflectivity of the resin dots. Not sure how that would work out.

I had been wondering previously whether some variation on a polarizing microscope of the sort used by mineralogists might work. I have a chunk of LCD screen and a heat gun, but outside weather is not cooperating and it definitely sounds like an outside job in the interests of domestic harmony.

I've tried illuminating from various angles, and that wasn't as helpful as I'd hoped. The best result previously was obtained by tilting the slide at an angle as viewing the droplets from the side makes them more visible. The downside here is that you only have a very small section of the slide in focus at any time.

First, I'll have a crack at sorting out the bed levelling using Probe Zero (a disposable hypodermic needle tip) so I don't munt the probe. 

Yes, disassemble number five. After smacking it around while investigating the probe height problem in the previous test the tip looks like this:

Well, damn. This is why we do not use micron probes for etching. I used the Probe Assembly Jig to get the probe out by the way, and it makes a decent Probe Disassembly Jig. May as well practice the technique on a damaged one.

This has implications for the previous test, in that it was unlikely I was ploughing the point per se into the marking dye. I have no idea at what stage I stuffed the tip, but I strongly suspect the initial touchdown into the resin-covered touch plate.

I'll make a new probe assembly using one of the acid-etched tips and try that out for resin deposition. Probably should image it after after the first touch and see what it looks like before I try depositing resin. It won't be anything like as accurate, but we'll see what data we can get out of it - particularly with regard to robustness!

The upgrades to the Y axis are done, by the way. I've added an 11mm booster under the tension bands to put more pressure on for anti-backlash. I added an extra band on each side too, though the little hook that they hang on to looks slightly over-stuffed with band.

If that works out, I'll put it on Github. Strange though that the other two axes don't show the problem. The Y axis isn't even the one with the highest loading.

I attempted a resin deposition run, unsuccessfully. This was due to a number of factors, most of which are visible in the following micrograph. This was taken with my phone through a microscope that cost me 30 quid from Liddell's, and focus is particularly blurry on the left, but it's the best magnification I can get:

 

This is an attempt at doing the "300μm" plot at a 10μm pitch using the acid/salt Nichrome probe. Why etch rather than deposit resin? Well, the height slope on the Y axis meant that the resin-dipped probe did not contact the surface, so I put down some Sharpie to see what was going on. 

Setup Issues at 1000V/mm 

During the Z-Touch phase I noticed that by dropping the probe speed to 2mm/min I could touch the foil reliably several times in the same location, but not if the tip was in resin. I think this is because the voltage will jump the air gap between the probe and the touch plate. Inaccurate rule of thumb suggests air breaks down and becomes conductive at roughly 1000V/mm so we'll go with that. The probe is at 5V, so at somewhere in the order of 5μm we'll start to pass current through it. The deceleration of the probe will stop it in less than 1μm, so by going sufficiently slowly the probe doesn't actually contact the foil much if at all - in air. On average.

The Y axis driver was noticeably  (or rather, audibly) unhappy. There was insufficient tension on the anti-backlash bands, and the Drive Screw was periodically binding on the printed flexure assembly. I'll relieve the binding and increase the height of the bar with the backlash bands on.

Resin Issues

The main problem was making contact some distance from the touch plate. The next problem was trying to tell what a resin dot looked like amongst the scratches and debris on the slide. Illuminating clear resin for imaging is tricky. Coloured resin tends to have pigment in it, with a particle size of ~5μm. So, no resin results today.

Accuracy Analysis

Proceeding with the probe and a Sharpie, the actual impact points are pretty well distributed along the X axis. I'd call that 10μm or near enough, and I'd hazard a guess to say I could position at 5μm or better without too much trouble. Except for the backlash. The tail on the micron character should be under its left arm. It misses by about 5μm on the X axis. That's the only dot that is subject to backlash. So it appears I have that much backlash in the system.

Levelling Analysis

As the probe strikes the surface at a 60 degree angle to vertical, it will move across it at roughly 1.5x the distance of the over-penetration. From the image, after 100μm of movement on the X axis, the probe skids roughly 5μm sideways. So there is effectively a 1 in 30 slope on the slide. The dirty hack would be to shim up the left side of the 25mm wide glass slide by about 0.8mm, and the proper thing to do (eventually) would be to provide for bed levelling.

So, a few things to fix up, then we'll try again. I'll post a picture of what the probe tip looks like after all this when I take the machine apart. 

While assembling those nice, pointy probe tips a certain amount of ... carnage was involved. I shall write "101 Ways To Trash Your Probe" at some stage. It became very worthwhile creating a jig, as it takes a while to re-make a tip (mostly in getting all the equipment out on the bench, mind). So I created this jig to hold a Probe Tip Arm in place while you glue the probe in it etc.:

The jig features a mark showing where the tip needs to be, and extensions to protect it as you work. Hopefully I have allowed enough clearance so you don't smash the tip on the side of the protective bits. Oh the irony.

The probe wire needs to be bent a bit so that it sits flat in the probe, and I'm just holding it in place with a bit of masking tape while I glue the probe wire into the Probe Tip Arm. I'm not sure if it's worth trying to make a tool to angle the probe tip. Let me know how you go.

It handily protects the probe while the glue dries and as you shuffle things around the workbench. I'm backing off now as our electricity is turning on and off like disco lights. The jig is on Github already as https://github.com/VikOlliver/RepRapMicron/blob/main/maus/maus_probe.scad

>Fzzzit!!!< CLONK WhrrrrimmmM!!!! 

Power Resumed

Sorry about that, folks. Electricity is back. The jig now has a slot in it to allow the Probe Beam to be fitted onto the Probe Arm without removing said arm, and you can nut the two together in the jig - admittedly a fiddly process unless you have a small nut driver. So anything that reduces tricksy handling of the probe manually is a good thing! There's also a little notch underneath so your finger can push the screw up into the Probe Arm. I've updated the Github.

 

I got some actual 316L stainless steel wire and some Nichrome 80, after the "Art of Bulshito" non-stainless non-steel wire incident. I decided to try etching them in either 1% nitric acid or 5% salt solution using the rig and instructions here on Printables. Using 3xAAA batteries for power, immersing the wires 8mm into the liquid, and with a stainless steel spoon/cathode 40mm from the liquid's surface. Blimey, wasn't expecting this:

 

Using nitric acid seems to produce a very robust probe tip, with an almost foamed shaft. There was indeed no cloudy precipitate during etching, but the tips of the wires did not fall off. What you see in the top photos is just the eroded end of the wire.

The salt was as cloudy as ever. The 0.12mm Nichrome dropped off at the meniscus. The 0.3mm Nichrome parted about half way down the immersed section.

The tips were gently rinsed with water and sprayed with isopropyl alcohol to remove any remaining liquid.

It appears that nitric acid is best for creating a robust tip. Nichrome creates extremely fine tips, but using wire as fine as 0.12mm diameter produces a very short tip that appears uneven and particularly delicate.

I think the most impressive tip of this batch was the very fine, spire-like tip produced by the 0.3mm Nichrome in salt. The tip is exceptionally small (too fine for the camera), the length has a gentle taper, and the sides look like they would hold a good dose of resin by capillary action. Here's an image zoomed in on that fine tip, with a piece of 0.3mm wire (almost in focus - sorry, it's hard) for scale.

That tip though is really fragile, and finer than I need - I had to make a jig to protect it during assembly. I wanted something half way between nitric and salt in dimensions. Well, lets put about 5ml of 1% nitric and 35ml of 5% salt solution together and... interesting. That stops the precipitate forming, and I can see the point sharpening nicely - hydrochloric acid might do the same and is easier to get, which I'll try later.

Anyway, that combination allows me to get a good tapered point, and tune its thickness to my requirement of the day. Now to join it to the μRepRap and see if I can deposit an even smaller resin Jolly Wrencher with it. 

Doesn't look as fragile as the long thin one (foreshadowing).

Yep, stung again by an Amazon supplier. Advertised as 0.3mm Stainless Steel Wire. Absolutely not, as you can see. Some plated copper muck:

 

So three spools of that can go in the bin. My first clue was that it started copper-plating the spoon, er, cathode in my electrolysis setup:

FYI I was using 1% nitric acid rather than my usual salt water. I intended to see if that would stop the production of cloudy iron hydroxide so I could tell when the end fell off the etched probe more easily. Turns out I need to try a different batch of wire, huh?

The objective was to find out how consistent the μRepRap was when using an aluminium foil touchplate. Simultaneously an overall difference in height was observed on the Z axis when the X axis was displaced.

A glass slide with UV resin-bonded aluminium kitchen foil burnished in place was placed on the stage and connected to the Z-Touch ground probe. 0.5mm approx of one edge of the foil had been bend right over prior to burnishing, presenting two layers of foil. There is a limitation here in that irregularities in the foil will cause cumulative errors in the height of the second layer of foil.

cnc-js was then used to position the probe over the foil, and Z-Touch data noted at 300μm intervals along the X axis on single and double layers of foil. The separation in the Y axis was 300μm, however it had to be manually adjusted in cnc-js by approximately 50μm due to inconsistencies in the preparation of the foil edge in the XY plane.

Repeated probing of the same point was not possible. The probe point cannot be instantaneously stopped, and deceleration after time of contact results in holes being poked in the foil.

The resulting data were crudely spreadsheeted.

Analysis shows that the difference in probe heights between the one layer and two layer probe points on the X axis was in the range of 10-11.7μm, suggesting that this technique is likely capable of locating initial probe Z height to within 2μm. 

Closer examination showed the Z values decreased as X displacement increased at what appears to be a linear rate given the sample size. Maximum vertical deviation was 28.5μm over an X distance of 2.1mm

Concluding, Z-Touch capability is suitable for at least initial probe height determination, and possibly may be sufficiently accurate for subtractive operations. If the probe tip is to be kept within 1μm of the surface, a working area of +/-75μm could be covered without compensating in software.

Note that the cause of this error is unknown. It may be that the stage is slightly tilted, or that tilting the stage will fix the issue regardless. However the Stage can reliably relocate within 50μm when homed, less than the distance for 1μm Z deviation. If the error really is relatively linear it will be possible to consistently compensate within 1μm accuracy - at least on the X axis.

Well I had a hypodermic needle probe in, and there was some resin, so I tried it as a deposition probe. Not very good results, wasn't really expecting much. Here's a micrograph:

 

Initial contact point is the top left of the square. White lines are probe tracks in Sharpie, blobs on the corners are cured resin. The sides are roughly 100μm a side (sorry, done manually) and so the blob of deposited resin looks to be roughly 30-40μm diameter. Not good enough. Will have to make a proper micron probe, which last time got me better than 10μm dots.

Aside on microscope image sensors: This cheap one (sub-Mpixel) I'm using here is heinously sensitive to IR light and grubby as all heck. If I try illuminating the sample with a halogen bulb it instantly whites out. Had to take this using the LED desk lamp. Better 23mm dia USB image sensor is on my Xmas list if Santa is listening... 

Every time I see those black and white micro scale images posted by the MEMS crowd I get a bit of calibration envy. The images all seem to have those really useful scale bars which provide an indication of the small size of things they are displaying.

Well, no more. I have added calibration tools to the software which controls the experiments in the FPath project and, henceforth, my images will now also contain a scale bar.

I just thought that some of you might be interested in how it is done. The video explains all:  https://youtu.be/nirIiC6hnc0  

The image below shows the scale bar in place while measuring the length of the claw at the end of a bee leg.(click on the image to enlarge, watch the video for context)

 

 

Labels: Feynman Path, FPath, millimeter scale calibration, Windows Media Foundation

I've been building up to a resin print test campaign, starting end of next week. So have been working hard on getting V0.05 into a usable state. Hardware is running quite happily down to 10μm per pixel, even in engrave mode. Here's the hackaday.io "Jolly Wrencher" logo etched into Sharpie marker. That's a 50x50 PNG done at 10μm per pixel, making the whole thing 0.5mm wide. Zoom in and you can see a bit of a gap between pixels, so I might even make 8μm.

 

 

This is a big little deal. Achieving 10μm is what I said I'd be happy with as a positional accuracy goal for this prototype. Of course, I need to get the resin going still. But the reason I picked that number is that it was the feature size of the original Intel 4004 CPU, and it seems to me to be some kind of tipping point.

Below is the new probe holder, allowing three degrees of freedom. The new probe holder requires you undo one of those vertical screws at the top to remove it, and requires a bit of fiddly setup to get the length right. But it is much more easily positioned over the UV source than the V0.03 design, and as V0.05 has such a massively improved range of motion on the Z axis you don't need to manually adjust it so often - just wind the Z axis up out of the way.

Below is the view I get on my "microscope" console with the print about half way through. The other console is taken up running cnc-js. Using mpv with custom pan/zoom macro keystrokes on the keypad instead of vlc has made the view much more useful.

Oh, note that the 10μm image was done using a 0.5mm hypodermic needle, not even a fine tip probe. That's the big, fuzzy grey thing centre to top right.

List of To Do's is growing a bit. I want to run resin tests using a hypodermic, after seeing how it did in the above test. I want to test Z Touch on a doubled sheet of aluminium foil to give me actual numbers on the thickness of the foil (which I shoulda done and never did). Finally, the bugbear of having to do version control and docs is getting kinda important.

Just as well I'm kept up at 3am by a helluva storm raging outside, ay? 

Update: Build files now on Github https://github.com/VikOlliver/RepRapMicron

Someone likes "Hello World"? Ok, a compromise. Here it is with some 3, 4, and 5 hundred micron markers. The markers are done at a pitch of 15, 20, and 25 microns respectively:

For a sense of scale, the "m" in "300μm" is about the width of a hair.

Attaching the probe was harder than expected. The eventual solution was to put it on a 20mm Metriccano Square Strip using an M3 x 35mm screw, adding a spring washer, and attaching that to the end of the Z Axis Driver with a nut. Tightening the nut raises the tip. Tip can be easily swung in and out by sticking a rod into the yellow block as a lever.

I adjusted Z height for the starting dot for each pass, getting lighter each time for smaller dots. With the binocular microscope it is easy to see that the dots get deeper as the probe tracks right. Possibly the slide wasn't quite level?

The other stand-out is the curling of "ld" which I'm unsure about but suspect stage rotation. More testing needed, but I think I need to get that probe in the dead centre next, so the UV LED will cure resin properly, and get a few mm of height adjustment.

Once that's done:

Make new fine probe tip, make new prepped slide, test Z Touch, and make some small stuff! 

I have to clear up desk space, so I though I might document the progression from the V0.04 axis driver through to what I hope is the reasonably stable V0.05 Linear Axis Driver. Here's the family portrait:

 

The good news is that the V0.05 is still mostly compatible with the existing V0.04 Table and Stage hardware. The major "Gotcha" is that the old Z Tower won't hold the probe in the right place. That's printing off as I write, and all being well I'll have everything back together tonight.

There will need to be some later structural changes to the XY Table to improve rigidity on the micron scale and resist rotation at extremities, but it's good enough to get on with some fabricating for now. Ideally I'd get a new probe holder designed, but if I can bodge it reasonably tidily to the point where others can easily replicate it and get on with depositing resin, that's what'll happen.

Some family business is coming up in about a week which will drag me kicking and screaming from my workbench. That will give me no excuse not to update the documentation and code. Should manage another blog update or two by then. 

Many mods and great results from the Z Axis Driver. I'm unable to see any lateral movement at all (with USB microscopes anyway) as the probe goes up and down. So far I've driven it from the Stage all the way up to 3.5mm, and it is such a relief to have a usable range that does not require me to manually position the probe tip to within a mm of the stage and tighten a clamp without shaking. I have no probe holder yet, it's literally just bolted on. Looks like this:

 

A lot of the holes are going away now I know where I want to mount things. This should result in a more rigid structure that prints faster and is less confusing to assemble. I'm happy enough to put a "V0.05" stamp on it and prepare for an interim release. 

New features 

From the left: In black you see a U-shaped bracket bolted to the end of the framework. This is an easily adjustable Limit Switch, enabling maximum usable range and simple realignment of the contacts in the event of a mishap.

Two holes right, you will see a couple of blue vertical cylinders; "Nut Bars." These are clamped to the frame with two M3 x 50mm screws, which add rigidity. The crossbeams above and below hold M3 nuts drilled out to 3mm which significantly limit the wobble of the drive screw and make the thing much less finicky to assemble (more on that later).

One hole right there are 3-hole long lugs that more or less allow mounting to V0.04 frame parts. Not perfect, needs a bit of shim, but functional.

Next we see the rectangular pair of complementary flexures. These constrain the moving end so that it can only move up and down. Coupled with the Nut Bars, these give the probe excellent stability and repeatability.

Completely missing off the right end is any kind of adjustable probe holder. You can see the small shiny probe tip, bottom right, and for now it's just held there with a bit of Metriccano and an M3 x 40mm screw. Unfortunately the increased length of the Axis Driver means the old mount no longer holds the probe tip near the centre of the Stage, so I've had to pull the slide out and examine it with a proper microscope. The dreaded "Hello World" (I swear I will do something else shortly):

Nut Bar Advantage

On that micrograph you'll see two obvious things: Smaller dots on the top image, and random displacement on the Y axis.

Y axis error is large because the Y Axis Driver lacks the lower Nut Bar. I'm replacing that driver with one that has a Lower Nut Bar right now.

Dots are much more consistent in size because the probe no longer oscillates. The dots are smaller at the top (approx 10μm dia) because I was able to position the probe more accurately. This was done using the new video workbench. If I push too hard on the surface with the probe tip, it starts sliding off to the left and the dots get elongated.

Video Workbench Height Determination 

I've switched to using vlc to mpv. The latter is better supported and allows me to assign keys to move around the image and zoom in and out easily (plus it doesn't use the accursed Flatpak). By zooming in on the one pixel at the very tip of the (now stable) probe, I can discern a brightness change in that pixel that is caused when the probe tip hits the glass slide and thus get a really good indicator of zero height.

As the Stage isn't optimally positioned, figuring that out that was tricky. But it should get easier once I've fixed the Z Axis Driver support structure.

So, get that Lower Nut Bar on the Y Axis Driver, Relocate the Z Axis Driver so the probe fits on the Stage, and we're back on track. I'll do a release then, unless anyone contacts me asking for files.