Homebuilt Lulzbot Mini

Making some progress on this! Turns out it may be a really easy mod if you don’t care about automatic bed leveling. but I’m planning on upgrading my electronics and switching to a bed leveling probe eventually on mine. More details on my blog.

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I am a retired instrumentation designer. If I was building my own mini I would mount the ‘Y’ limit switch to the frame rather on the bed which moves. The wire to the switch on mine has broken twice. It is wrong to mount switches on moving objects. The other wires need to be there of course to heat the bed etc.

All good points. If i was starting from scratch i probably would try to think about that more. There are many places where the lulzbot designs could improve a lot, and you make a good point about limit switches and mounting. I personally have never had my wires break from movement, but that may all be a matter of time.

You may not have noticed that this is a really old thread that has been revived to mention the mod of the metal flexible prusa bed plate over the old glass bed. Partially because Lulzbot refused to sell me a new aluminum bed plate for my Lulzbot mini 2 upgrade. Partially because metal bed plates are better, and it was actually way cheaper to buy prusa parts from Europe than it was to buy them from Lulzbot in the U.S. Imagine that.

what i didn’t mention before though (but is mentioned on my blog) is that i am also independently planning on upgrading my mini rambo board to a EINSY Rambo, which is the same as the Prusa i3 MK3S. The Lulzbot Mini 2 uses the Einsy Retro which is basically the same except for a few connector differences. The new trinamic stepper drivers on these boards may allow for the possibility of having no limit switches at all. I’ll have to check if the prusa machines are doing that by default now or not. But if not, it probably is an easy change in the marlin firmware.

I’m not a 3D technophobe. What is gained by replacing the control board? It may be something that I should look into. So far the mini has done everything that I have asked of it although until Covid I only made toys for kids really. Lately I have been running it 8 hours a day printing ‘ear savers’ for folk who have to wear masks.

The biggest for me is the trinamic stepper motor drivers that tune the motors much quieter. That would be worth the upgrade alone from what i hear.

The second advantage for me is the ability to add an LCD screen. My original rambo mini is pre 1.3 and as such does not have the correct pinout for an LCD screen.

But i am also interested in using a magnetic bed leveling probe. But that is a mute point.

Thanks for the reply.
I had no idea that the futuristic sounds coming from my mini were caused by the control board and to not hear that would be nice. I don’t feel that I need the LCD screen as I use Octopi and find it very convenient.

lol. Yeah, i haven’t tried them myself yet, but the trinamic drivers sound really nice. My new Prusa Mini is nearly silent. https://youtu.be/sPvTB3irCxQ

I also use Octopi, but i like the idea of an LCD for changing filament and other nice features. Not needed, but nice when you do.

Update on my blog:

I’m currently in the process of reporting what i believe to be a bug in Marlin firmware. I encountered it when i went to center my new prusa mini bed plate.

Just wondering if you have any info regarding the purpose of the U2 pins shown on this board. I ask because I had problems the bed temperature instability and could find nothing obviously wrong with the wiring or thermistor however while looking over the electronics board I did notice that the plug attached to these pins was almost off because there in no locking mechanism. When I reassembled everything, and after refitting the U2 cable connector, my problem was gone. This may be coincidental and I may still have a wire in the process of failing.

I just looked at a spare mini Rambo board I have. I believe U2 is actually referring to the Atmega chip. But if it is the only connector connected to the 6pin header right next to U2 with no locking mechanism then yes I am familiar with it. If I remember correctly it actually goes to the lower z limit switch and the two pins it is connected to actually go nowhere. It is a dummy port basically. The z-min switch actually goes to the bed leveling probe / hotend. So in essence you have a limit switch that does nothing. Probably coincidental as that was probably not your problem.

I made a big stink about lulzbot continuing to wire up zmin switches if they actually do nothing. Lulzbot no longer even wires them up anymore now.

Honestly though it would be nice to have limit switches for safety. Wiring it to the bed leveling probe seems like a hack to me and not real engineering. But I guess some other 3d printers may do the same.

Thanks for this info. It’s very weird that they wired this and used the wrong type of connector to do it to boot, and yet it has no purpose. I’m guessing it was to do with bed levelling but got superseded by some other method, but never decommissioned. Its confusing because I have no wires below the bed, looking for a place to go. Right now everything is working fine but next time I have it apart I’ll take the time to trace out where those wires actually go.
I am thinking that I should probably order a complete new bed as a backup as although mine is working right now, I have sanded it lightly many times to improve grip. Is Lulzbot the only supplier do you know? I see that they are currently out of stock.

I think lulzbot has stopped making the old heatbed in favor of the newer 2-piece modular system. https://www.lulzbot.com/store/parts/lulzbot-mini-etched-modular-print-bed-heater

ItWorks3D is a pretty good place to look for lulzbot parts. They probably have the original style heatbed for a decent price. I haven’t used the modular system, but I think I would go that route if I wasn’t doing my Prusa mini flexible bed mod. It would make it nice to replace cracked glass but not the heater. Plus you can flip it over bare glass on one side and PEI on the other.

I went ahead and ordered a heater/bed assembled from IT-Works 3D mainly because Lulzbot are out of stock. I’m sure that it will fit my needs for now anyway although I do like the modular idea. Damn shipping is expensive for it though, 30% of the total bill!

Can anyone with a lulzbot mini check my marlin 2.0 bug for me? I would really appreciate it. Thanks!

My mini came with two seemingly identical print heads complete. In the docs, ‘EO’ = 833. Can you tell me if this value for the print head that it came with it or is it to do with something else? I can seem to find any reference to ‘EO’ in the Lulzbot docs that I have. I am wanting to try the other print head but not sure of the precautions/setup that may be required.

I’m not sure what EO stands for but 833 is a value I recognize for E-steps. Usually LulzBot would put a sticker with the E-steps value for each tool head on the back of the mounting plate (so you can’t read it when the tool head is installed).

It is E steps. I just couldn’t recall when I was typing:) The spare toolhead has no label on the rear, but I’m guessing that there must be a way to calculate what they should be? I’m guessing it’s a fine tuner for extrusion but not sure

Yeah 833 is pretty close to the calibration for the steppers lulzbot uses. There is a calibration procedure in the OHAI docs if you want to fine tune it.


Actually, it’s not the stepper that affects the calibration, it’s the diameter of the hob bolt. Some of the newest tool heads based on the E3D mechanicals start at around 420. The older hexagon mechanicals are in the 800-850 range.

Thanks for this. I will give it a try once I get the Covid stuff under control.