Friendly warning: Mind your Z axis smooth rods  

Friendly warning: Mind your Z axis smooth rods

Hey guys,

I've just found out one possibly big problem with my assembly of MK3S and fixed it. This is just to let some poor souls out there know what to look out for (It was not in the manual).

The Z smooth rods were not pushed properly into the holes near the Z motors. This is not an easy task, as you are supposed to do it with the motors with lead screws already installed on the frame holding on just the 3D printed holders. This caused the top rod holders to be very hard to mount on the frame and the rods. This might cause following issues:

• Random crashes on Y axis if both of the Z rods are off by a similar amount (the Z axis would lean forward).
• Random crashes on X and Y axis if the Z rods are off by a different amount (the Z axis would lean forward and to a side).
• Turning crash detection off would result in various but consistent amounts of shifts on just Y or both Y and X axis.

This is what I did:

• Turn the printer off (we'll be rotating the Z axis motors by hand which is not possible with printer turned on, also is dangerous).
  Move X axis down with extruder down by rotating the Z axis lead screws, nozzle some 2cm above the bed. This is to move the weight to the bottom so the threaded rods are not deformed.
• Dismount the top holders.
• Carefully pull out the smooth rods away from the bearings (you can probably just pull them out a little without removing them from the bearings, but it'll make eventual cleaning of the hole at motors a bit harder).
• Clean the holes with a drill (by hand).
• Remove pieces of filament with pliers, tweezers and compressed air.
• Inspect the image below, the smooth rods and lead screws are not supposed to be aligned (smooth rods are a little bit higher; mine are 2mm higner).
• Hold the motor of the Z axis with one hand and push the smooth rods back.
  • Be careful with the bearings if you have removed the rods from them).
  • This might need some force.
  • You can also put something firm under the motor before you start pushing the rods into the plastic.
• Move the X axis with extruder up about 10cm below the frame by rotating the Z lead screws manually. This would align the rods on the top better and helps you spot additional problems with X axis rods.
• Put the top holders on the rods. The should just smoothly click. In my case the frame screw holes were not aligned with the holes on the holders (slight shift to side). I manually turned one of the Z axis lead screws. This would move with one side of the X axis up down and as a result it would lean the rods and the top holders to sides to a align with the holes.
  • Be careful here, if you don't see the SAME alignment with frame holes on BOTH top holders, your X axis might be pushing the Z rods away from each other. Most likely the rods on the X axis are not pushed fully into the holes on the X axis holders. In this case you'd probably have to dismount the Z motors in order to pull X axis off and disassemble it to push the rods in fully (it's a pain).
• Once the top holder screw holes are aligned well with the holes on the frame, the top holders were sitting nicely on the rods (try to take the holders off and put them back on a few times -- they should just click smoothly). The frame screws should go in without any additional alignment needed.

The rods are not aligned on top even in the 3D model. My smooth rods were some 2mm above the lead screws.

Hope this helps, cheers.