RepRap: Blog

New microscope exchanged by Jaycar with no problems. Homing the axes however, problems. Notably my brainwave for just running the axes out of the drive nuts produces so much vibration the nuts move, and the drive screws won't reliably go in again. In fact it vibrated a mounting screw loose!

I guess I'll have to do it properly and put switches in the base. *Sigh!*

# posted by vik-olliver @ 8:34 AM 0 comments

 I've uploaded the build files for Titch's main body and base. I have also created a collection on Printables of the parts used in the project so far. Please join in.

# posted by vik-olliver @ 6:40 AM 0 comments

I've published the files and assembly details of the glass slide holder on Printables here.

# posted by vik-olliver @ 11:35 PM 0 comments

No microscope, so I thought I'd noodle around with some useful bits of 3D printed hardware. Looking for a way to hold the glass slides in place.

Now I've settled (for the moment) on squares of glass microscope slide, it has been worth developing a holder that will clip them to the Block Stage platform. I came up with this little clippy gadget which I have given the snazzy name "Glass Slide Holder." 

Once I know how well it works I'll post the files on Printables.  Why is one corner sliced off? Because it would collide with the probe platform.

Be nice to test it out, but without the microscope I can't see a damn thing!

# posted by vik-olliver @ 7:01 AM 0 comments

The illumination in the USB microscope/macro camera that I've been using has failed. Should be under guarantee, but development this weekend is now slightly embuggered. I'm sure Jaycar will get a replacement in fairly promptly, have good working relations with them.

Just before that, I was measuring how much height difference I was getting in a 0.4mm radius. Looks to be about 0.02mm which is not terrific. So we're looking at a 5% slope, roughly. Once the microscope is back, we'll see how easy it is to compensate in software.

Just realised I can use the probe to draw calibration marks for re-zeroing the probe. That might help.

The glass microscope slides turned up too. I've cut one into 1/3rds (basically inch squares in old money) which *just* fit on the stage. Will probably make a holder with clips for them that screws on to the stage, as I'm currently holding them there with blue tape...

# posted by vik-olliver @ 1:34 AM 0 comments

I've made a holder that clips onto a standard 40mm, um, biological sample pot. This suspends the wire in the electrolyte and gives you an easy way to hold the wire at the right level with the positive croc lead. Makes probe tip manufacture a heck of a lot easier. Files and process on Printables here.

# posted by vik-olliver @ 11:42 PM 0 comments

I have *a* way of levelling the axes on the Block Stage: Drive the motors until they back the adjustment screws out of the drive nuts, at which point the motor just spins on top of the drive nut. Then drive them back in half way. Crude, noisy, probably good to only 100μm max, appears to work...

# posted by vik-olliver @ 11:13 AM 0 comments

I've bent a few probes now. They're delicate little snowflakes. So I've created a storage spigot and added it to the probe arm files. This spigot can be glued inside a pill container lid to allow the probe to be protected by the container without rattling around:

# posted by vik-olliver @ 12:49 AM 0 comments

Scrappy innit? I could tell from the microscope that the probe was tracing out a square, however point contact is a bit patchy - don't expect to see individual 20μm squares as this is a rigid chonky tip.

As this was scanned in both X and Y, we can pretty clearly see that the probe is too high in the top right corner of the image. Rough sums as follows:

Height of stage: 75mm

Travel from centre to endstop: 2mm

Therefore Pythagoras tells us 0.025mm height variation on the flexure stage.

We're moving 0.2mm here, so we'd expect a height variation of roughly 2.5μm, which feels about right. A few more test patterns required, and a way of actually making sure I'm properly centred to get some consistency. Perhaps a pattern of groups of concentric squares varying in height?

# posted by vik-olliver @ 10:26 AM 0 comments

So I've tested out the new probe holder fitted with with a fairly broad etched tip. Back to a glass slide, which I have to mount sideways to fit on the stage (more on order).

Over 400μm of logo I'm noticing a roughly 7μm variation in probe height. This might be due to my stage not being perfectly level, or the stage dropping slightly as the X and Y axis move. That should be a very small effect but I'll have to run the sums because 7μm is indeed very small.

If I make smaller things though, the Z height variation will be less in proportion. Still, here's what the test looked like. I'll run up a proper test grid and run some off with the axes positioned at different maxima and minima. See what's actually going on.

Speaking of which, I'm starting to get annoyed about not being able to "home" the axes, so that might happen in the near-ish future. Personal life getting in the way of that.

# posted by vik-olliver @ 1:01 AM 0 comments

I've added a probe socket to the probe arm files.Partly because I wanted to stiffen up the wire probe tips I'm making, and partly because I realise that hypodermic needles are not universally available. These press-fit onto the end of the probe arm.

The probe wire can either be just wedged in the slot (which conveniently tapers inside), glued into place, or melted into a spludge of plastic with a soldering iron.

# posted by vik-olliver @ 7:51 AM 0 comments

I may be blaming my tools here, but I'm running into a persistent problem with my clever idea of using glass cover slips: They seem to be uneven. Or the cheap batch I have are anyway. This might not normally matter, but when you're controlling the probe height to a micron or two it can be a pain in the butt!

I'll have to switch back to slides. Which means I'll have to cut some down because a whole slide won't fit on the new stage. Or make a new stage, I suppose. I'll have to fork out for more slides eventually as I have like one spare and all the others have really interesting specimens on...

# posted by vik-olliver @ 9:58 AM 0 comments