Strange Z-axis reversals on old Mini 1

I recently obtained a pair of old Mini 1s (a 1.03 and a 1.04 I believe). I’m trying to resurrect the newer of the two. The Z axis positioning is unreliable. It will reliably home using G28. If I then traverse to e.g. G0 Z10 and then back to G0 Z150, it will usually work, but occasionally runs in the wrong direction, often causing the nozzle to crash into the bed. I have seen it flake out in many different ways, e.g. start going in the wrong direction and then suddenly reverse, or for small traverses go in the right or wrong direction unpredictably. I even had it run a whole print successfully, and then just as it finished instead of raising back to the resting Z height it smashed the hot nozzle into the test print.

From other comments here it sounds like this could be due to the driver chip overheating (Mini 1 Z-axis fail) or general board failure (Mini 1 Z-Axis "Chattering" - HELP!!).

However I also hear some vibrations coming from the left Z screw. I just cleaned and lubed both z screws. So the question is, what should the next steps be for diagnosis? Any tips for discerning between mechanical problems with the z screws, bad stepper motor, bad connections, or bad board?

Thank you!

There wouldn’t be a mechanical problem that I can think of that would reverse the direction, especially not on both motors simultaneously.

Driver/board issue would be my diagnosis. I don’t think a failing Z-max limit switch would cause this sort of issue.

I wouldn’t put much work into a Mini 1. Mini 2s are great workhorses though. Unless you have real reason to keep using the Mini 1s, I’d really suggest putting effort elsewhere.

Wrathernaut, thank you for your candid advice. The only reason to work on them is that I have them, and I’m learning a lot about 3d printer design. As a last resort I will scavenge the parts for other projects, but I think the next step is to get a modern controller board and approach this as a sort of DIY build. Thanks again!

An skr turbo with bltouch, and sensorless homing configured would be fairly easy if you have any experience doing Marlin builds. Keeping the washer -based leveling is usually the worst part of doing a custom build on lulzbot machines, and usually the part you want to get rid of.

That’s encouraging. I just ordered an SKR pro board before seeing your post. Ironically I did so because it has all six endstop ports. Curious why the washer leveling is the “worst” part. It does seem like the wiping routine preceding leveling could be rather hard on the y axis, and that in general the conductive test might not be as foolproof as one would like, but I’m just guessing.

I already tried running klipper on my flaky old board, and was somewhat surprised to see that the ABL washer routine worked with the included config. So I find myself asking that dangerous question, “how hard could it be?”

Or is it simply that you feel BLTouch is better?

Washer leveling just fails frequently due to any sort of plastic throwing off the measurements. Wiping just isn’t effective enough, and each filament color and brand (almost roll to roll, even) has such a narrow temperature range where wiping works that doesn’t let more ooze out before probing.

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There’s a Youtuber, I think the same guy who writes the Lulzbot educational materials, who recommends using red 3m abrasive pads to wipe down the nozzle. He claims it doesn’t damage the nozzle. Well, I can for certain testify it will absolutely ruin even steel nozzles. I even tried using “non scratch” white painters pads and even those will tear apart a brass nozzle. And I think these are the same pads they use on the newer Taz printers. I don’t know what the solution is to consistent probing without intense intervention every time you print. Probably some combination of cleaning the nozzle after each print while the nozzle is still hot followed by an equal amount of cleaning before each print. Using something VERY soft in the process.

If you took time to look at the printed parts that come with Lulzbot printers, looks like they struggle too to get the probing to work properly. My Taz Pro XT has some of the worst elephant foot on printed parts I have ever seen. Like, I question how these parts made it out of QA. The ones on my Taz 6 were perfect, super clean printed parts. Something has happened over the years since then.

This was all super helpful. Thank you both!

I had good results with using red scrub pads when I was using washer leveling when combined with the Slice Engineering Vanadium nozzles. They were pretty good at resisting plastic in the first place, but at how tough they were, I wasn’t worried about wearing them out.