RepRap: Blog

After seeing Jon struggle to fit the Flexure Coupling to his RepRapMicron  stepper motor, I've reached the conclusion that relying on precise printer dimensions for shaft fit is foolish. Coincidentally, I appear to have stressed my X Axis Flexure Coupling to the point where it cracked (see black mark):

This was caused by me tightening the Drive Screw down too much, but spurred me to modify the Flexure Coupling to have a conical hole in it (on github and Printables). The gentle taper makes it easier to start pushing the motor shaft in. The downside is that different printers and shafts will bottom out at different points. Still, there's a few mm adjustment in the design, and spacers in the print file for adjusting for gros shaft length.

The cracked flexure also explains why my X backlash increased after I fiddled with the Axis Driver. I'll fit the new one and see if that fixes it.

The main moderator of this blog has had to retire for personal reasons. I'd like to take the opportunity to publicly thank them for all the work they have done not just for the blog, but for The RepRap Project as a whole. You have my respect, and I wish you the best possible future.

Sincerely,

Vik Olliver 

The python script to create X & Y axis verniers for detecting backlash is up on github at https://github.com/VikOlliver/RepRapMicron/blob/main/utils/backlash_vernier.py

This has allowed more detailed examination of the backlash (line spacing is approx 80μm):

The first set of lines (upper or left) spacing increases by 0.5μm each time. The other set is at a constant spacing. Each set is drawn heading in the opposite direction to its partner. So the left set spaced on the Y axis aligns with the second marker (1μm) and the right set aligns at the 4th or 5th marker (2.5μm).

As they're headed in different directions, the relative backlash is doubled, so backlash on Y is 0.5μm and on X 1.25μm. I may need to increase the strength of the backlash bands on the X Axis Driver, but frankly for this stage of the game I'll only do that if I have to take it apart or realign it for some other reason.

FYI The slightly kinked line roughly in the middle of  the leftmost horizontal set is where I bumped the bench.

I drew a series of vertical lines spaced at 100μm plus an increasing/decreasing delta, hoping to create a kind of vernier scale. The upper lines were done left to right, the lower ones right to left. Yes, I need to level the bed again, still haven't got round to it. Also need to glue the magnets down because they're moving, which should not matter but just in case...

The results here, to my immense surprise and joy, show no discernible backlash on the lines at each end, which are the ones that are supposed to line up if everything is aligned properly with no backlash. There might be a bit, but it's within the "noise" of dragging a probe across the surface subtractively.

I'll have to check my algorithm because the spacing looks a little wibbly, and do one for the Y axis as well, then post the vernier generator on github. Still, it's consistent behaviour, and nice straight lines, which I will take as a win.

Found the loose screw on the X Axis Driver. Re-doing the grid produced something quite a bit nicer. Still not perfect, but it's shaping up and close enough to proceed with some backlash testing:

Again, that's a 10x10 grid of 100μm squares. Line widths are a tad more consistent now I've fitted a temporary part to compensate for my mis-printed PIKA Z Tower, thus improving the probe angle.

Little divot in the bottom left is just me figuring out where the substrate is.

I could probably make a 1mm QR code... 

I fired up the PIKA and ran a test grid. Been having a few camera issues after the laptop upgrade, but that's sorted now. More generally useful stuff on that in a later post, TL;DR vlc, mpv etc. aren't doing what I want so I've hand-rolled something.

The python script for creating the grid GCODE is here: https://github.com/VikOlliver/RepRapMicron/blob/main/utils/grid_gcode.py

Here's a 10x10 grid of 100μm squares etched into marker using Probe 9:

 

Spacing is pretty good on the Y axis, but the X axis needs a bit of love. The X deviations seem to be regular, so I suspect I just need to centre the Drive Screw a bit better.

Line widths are different on the X and Y axis this is because my particular PIKA prototype has the Z Tower 2mm too close to the centre and I have to tilt the probe at an unholy angle to get it in contact. The PIKA chassis takes a lot of printing, so I'll probably print a temporary probe assembly to work around that, which is a much smaller part.

The actual consistency of line width (given this is subtractive scraping) is reasonably constant over a 1mm square, though does fade out a bit towards the top right. My office got unreasonably hot yesterday, so I think I may need to re-level. 

Just to help Jon Oxer out during https://www.youtube.com/watch?v=r19WoewJ_Ys. These are the photos of the V0.01 PIKA Base assembly and Axis Driver integration that I took for the docs:

 

No code changes, just ran it. The old 30μm/pixel version, 1.2mm long . So, backwards compatible.

 Used a hypodermic needle probe, so not the most elegant or fine dots, but well spaced.