RepRap: Blog

In an attempt to make a more rigid probe, I started with some 22 gauge (0.6mm) "Nichrome" wire. This took nearly a quarter of an hour to corrode away in the electrolysis cell, and when the end finally fell off it looked like this:

You do not have to be an expert metallurgist to see there's something ... interesting going on in the manufacture of this brand. There is a clear spiral pattern to the erosion, and fibres of incompletely mixed metal in the alloy. While sold as Nichrome, the packaging itself only states "Resistance Wire" and it appears that resistance is futile.

I'd recommend getting wire from a manufacturer that states the percentage of nickel and chromium, and make sure the numbers add up to 100.

# posted by vik-olliver @ 3:12 AM 0 comments

I found a limitation with jscut in that it always closes a path, so if you draw a 'U' it will join the two ends at the top. So jscut is not suitable. After looking for something that works, I found that PrusaSlicer imports SVG paths (though they need re-scaling for undetermined reasons).

So I wrote a RepRapMicron printer configuration for PrusaSlicer based on Marlin and told it not to use the extruder. It put 'A' commands and 'M' commands in the GCODE though, so I used a post processor to strip them out:

/bin/sed "s/ A[0-9.-]*//";grep -v "^M"

This allowed me to import an SVG line drawing and produce this:

 Due to the probe impact problem producing a bloody great horizontal line every time it hits the slide, some things are a bit obscured, but that's a 500μm line with end marks and the letters "500um" underneath it.

So now I can draw open-ended paths and can get on with creating some calibration patterns manually.

I also really need to print a microscope slide storage box to take to Everything Open. Must remember to set the printer type back...

# posted by vik-olliver @ 12:13 AM 0 comments

Happy New Year! Is there anything that I should put at the top of my New Year's Resolution list to release, document, or improve things that you want to see? 43 people have checked the new git repo, please do tell.

I wrote the GCODE for a calibration zigzag, 500μm lengths, 50μm spacing, repeated along X & Y with a staircase gradually lifting the probe by 2μm for each segment. I ran it twice, and took an image of the calibration slide with the same camera settings:

Immediate things, X scale is off, the lines are only 415μm long, not 500, fixed that in GRBL config.

Lighter lines are generally more consistent, which figures as less stress on the probe.

Y axis seems to have consistency issues being +/-30μm. Needs an overhaul. I'll probably do a diagonal calibration slide later to test the overhaul. Even so, that's literally within a hair's breadth.

[Edit: It seems one of the bands used for backlash has broken, which is going to tilt the drive nut...]

But the X axis, other than the scaling issue, seems to be positioning +/- 10μm absolute which I am moderately happy with for now.

Start point divots are reduced, possibly by a 5x reduction in plunge speed. I noticed a lot of vibration of the probe through the microscope. Not sure how much of that is the axis mount, and how much flexibility in the probe, but both need to be addressed.

I'll take a peek to see what's up with the Y axis. Now I have had experience in handling the setup, I think I might risk a decent probe with a more symmetrical cross section and see if that improves things.

This all brings to the fore the question of end stops, so that I can guarantee the same starting point every time and thus experimental consistency.

# posted by vik-olliver @ 2:33 AM 0 comments