Prusa assembly notes

[last updated: 2018-12-12]
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(link to:) Prusa Mk3 Assembly instructions
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Note: Prusa assembly documentation is great, organized in clear sections, with every step user-friendly, very clear even for beginners. Especially helpful are the comments from users following every step, so you can see problems that other people have had, and what's worked to fix them. I recommend reading the comments before starting a step, so you know what to watch out for.

That said, after the Pre-Flight checks, documentation on subsequent procedures is nebulous and difficult to find. I did manage to find what I needed, and I've included links here to help anyone struggling as I did to find out what to do next after a given step.

• Y-axis Assembly: started 2018/09/06
• Assembled the Y-axis frame, but then (step 10) you need to check the level/alignment. You're supposed to put it onto a "flat" surface and see if it wobbles. Where do you find a flat surface?? I have an old marble-topped cabinet, and thought the top would be about as flat as anything.
• My assembly did wobble a tiny bit, and no amount of loosening and adjusting and re-tightening eliminated the wobble, so finally I put a 35lb hand weight on a board laid diagonally across the frame. It worked well. Not perfectly, still a tiny wobble, but way way better than before.
• Electronics:
• Broke off the pin in the lower hinge for the electronics compartment door. It will still hang and be functional with just the top hinge and the final long screw in place, but I'll need to repair or build a replacement at some point.
• Build is complete!
• Pre-flight:
  (link to:) Prusa pre-flight instructions
  • Adjust pintle height:
  • The pintle is a proximity sensor (digital = on/off) that "triggers" when its face is some set distance above the bed. As the extruder moves down, the pintle senses when it's at the correct height, and stops the downward movement when the nozzle is the correct distance above the bed. If the pintle is set too high, the extruder assembly and nozzle will get down too low before the pintle senses the bed and triggers to stop downward movement, with consequence that the nozzle may crash into the bed. Not good.
  • Online comments show that the first step, adjusting the pintle height, is problematic, with questionable, ie. difficult to adjust, engineering in the mounting of the sensor, and instructions less detailed than needed, if not ambiguous, such that users are left to kind of figure it out themselves. Here's what I did:
  • Moved extruder all the way left, then lowered it to nominally 1/4" above the bed. Put a sheet of 20# printer paper (about 0.0042" = 0.107mm) under nozzle. Lowered the extruder/nozzle until I could just still slide the paper. Moved extruder to the right, continuously monitoring height above the bed with my paper shim, and adjusted right Z leadscrew to keep paper just able to move.
  • When this step is done, right & left z-axis leadscrews will be adjusted such that the extruder rails and side-to-side movement are perfectly parallel to, and the nozzle is the correct distance above, the bed. Now adjust the pintle height.
  • Online instructions say to adjust pintle to a height equal to that of the thickness at the middle of a zip tie (0.045" = 1.143mm = 10.7 sheets of paper by my measurement).
  • However online comments suggest pintle needs to be lower, like maybe 0.65mm = 0.026" = ~6 sheets of paper.
  • Split the difference between 6 and 10. Moved extruder to center of x-axis and adjusted pintle height to 8 sheets of paper.
  • As online comments suggested, I used a screwdriver to pry open the slot clamping the pintle, to release it and allow the pintle to move.

• Finished all 9/11

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eof