RepRap: Blog

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. 

# posted by vik-olliver @ 12:01 AM 0 comments

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.

# posted by vik-olliver @ 11:04 PM 0 comments

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. 

# posted by vik-olliver @ 9:30 PM 0 comments

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:

# posted by vik-olliver @ 6:26 AM 3 comments

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.

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.

# posted by vik-olliver @ 12:04 AM 0 comments

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... 

# posted by vik-olliver @ 9:34 AM 2 comments

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

# posted by OfItselfSo @ 7:47 PM 3 comments

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

# posted by vik-olliver @ 3:29 PM 4 comments

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! 

# posted by vik-olliver @ 8:26 PM 2 comments

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. 

# posted by vik-olliver @ 12:41 AM 2 comments

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):

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. 

# posted by vik-olliver @ 12:16 AM 1 comments