Z-axis not moving up accurately when printing

I was having problems with the print becoming “squished”. It resulted in a part (say) 10mm high ending up (say) 8mm high with one or more layers being chewed up by the nozzle because the Z-axis wasn’t moving up the correct distance between layers. The fault was intermittent and seemed to occur about 40% of the time I ran the printer. After trying all sorts of software fixes (none of which worked), greasing the threaded Z-axis rods (lithium grease) and cleaning the smooth rods with IPA, the problem remained. However, I think I have finally found the problem. I carefully removed the plugs that go into the base of the two Z-axis stepping motors and cleaned them (these white plugs simply pull out). I then repeated the cleaning operation on the black z-axis plugs that go onto the Rambo control board. (You’ll have to open up the case).Fortunately the cables are labeled. (Note to remove the two black Z-axis plugs on the Rambo board you have to depress a tab under the plug (you can’t see it easily, but you can feel it). Don’t just keep pulling at the plug, and certainly do NOT pull the wires entering the plug). Work slowly and carefully. Cleaning method: Add a few drops of 91% IPA to the pins in the socket, and a few drops into the holes in the plug. Wait 10 - 20 seconds and blow away any remaining liquid with compressed air. Repeat. Carefully replace the plug in the correct socket. Be gentle and don’t force the plug or you might bend a pin which could mean a new Rambo board! The plugs go in very easily.
So far this seems to have resolved the problem.
Here is a" before and after" photo of part of a key holder:


At first I thought this “Squishing problem” was related to the way the printing head retracted after the print had finished (in multiple vertical steps, rather than one continuous action), but it doesn’t seem to be. For more details on this see my posting of about a week ago.

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Having a similar issue on the Workhorse :frowning:

Let me know if cleaning the Z-axis connectors on the Rambo board and at the motors’ end works for you. So far it has worked for me. I live in downtown Cincinnati, sandwiched between two freeways, so the air is pretty polluted and with the fan pulling in air to keep the circuitry cool, I figure it pulls in enough oily pollutants to compromise the connections between plug and board. Thus, the Z-axis misses a few pulses each time, and the missed pulses accumulate, which is why the problem got worse as the height of the print increased. The plugs and pins are, incidentally, budget priced nickel plated, not gold plated, the former being more prone to poor connection. My Mini is about 2 years old and the only modification is the addition of the GLCD. I was using PLA as the print medium.

Interesting info. Thanks.
What is the GLCD mod that you mention?
Also where I live IPA refers to beer but I doubt it would be the best thing to clean contacts with :slight_smile:
Barry

If you compare the Mini 1 with the newer Mini 2, you will see that the Mini 2 has a small black box fixed to the top right of the frame. This is the GLCD (Graphical LCD), and is available as a bolt-on to the Mini 1 model. If you buy the GLCD (available from Lulzbot) you no longer need to connect your Printer to your computer. You can download your design in G-code to an SD card and stick that in the side the the GLCD box. Much more convenient. (The GLCD also allows you to control the printer in other ways too).
IPA is short for Isopropyl alcohol and can normally be bought from any pharmacy as either 70% solution or 91% solution. It is also known as rubbing alcohol. If you drink it, it will probably kill you; and if you clean the contacts in your printer with India Pale Ale (IPA) it will probably kill your printer. Take care you choose the right one! :open_mouth:
By the way, Cleaning both ends of my Z-axis contacts seems to have completely fixed my printer - not a failed print after cleaning. :grinning:

Thanks. I did consider adding the control box to my mini when they were on sale a while back but I had just setup a RaspberryPI with Octopi to do the same thing more or less and for me I think it works better. I hooked up an old webcam to the pi which already had wifi so now I’m able to view what’s going on from any device in my house basically.
The finish on some of my prints are a bit like your ‘before’ shot but since I’d never seen anything better I assumed that to be normal. I purchased my mini used and not working. Had to fix a broken wire going to the X axis micro switch. Maybe I will clean up the contacts and see what happens.