Hot-End/Bed Collision - Z axis travel problem?
I received my Prusa i3 MK2 kit a few days ago. The build went pretty smoothly and having slackened off the nuts and doing various 'tweaks' back and forth, I seem to have the whole structure square and true. The only casualty was the right-hand front corner block which cracked through due to the tightness of the Y rod!
The self-test passed first time but I am having a great deal of trouble with the calibration. The hot-end collides with the bed in the Z move every time and at every point. Despite doing this with the hot end cold, the bed surface has inevitably sustained some damage which is rather upsetting.
After much checking and diagnostics, the following is what I seem to be experiencing -
If I run the Z axis right to the top (until the motors clack) the Z-move screen shows +210.0 which I assume to be correct. If I then run the Z axis down until it just touches the bed surface the display reads +002.0 This is consistent in all four corners of the bed and in the middle. I assume that it ought to be able to reach 000.0 and that should be when just in contact with the bed.
I have checked that there is no further movement available of the M10 studs down into the slots of the frame and checked all the other possibilities for movement through mechanical adjustment. The only thing I wondered about was if it is correct that when sent to the top position, the top guide blocks actually encounter the 2 screws each side that hold the two top frame rod blocks in place rather than the cut-out on the block itself. The difference between the two would probably account for the missing 2mm of travel. Does this sound like the likely source of the problem or am I missing something else?
NB I have also altered how the tie-wraps hold the slide-bearings on to the bed support just to make sure that the cut ends of the original tie wraps were not making the bed sit high - and I have checked that the bed PC is seated well on the bed support and the assembly looks unstressed and nice and flat.
I have watched various You-Tube videos including those from Joe Prusa himself and Thomas Sandalier but have not found anything specific about this problem.
Any suggestions would be greatly appreciated as I thought I would have been up and running several hours ago 🙂
Adrian
Re: Hot-End/Bed Collision - Z axis travel problem?
Does the inductive probe work? In inactive (not triggered) state you should see red LED light coming from its upper end (where cable comes out). When triggered, the light should go off. You can manually trigger the probe by putting metal object (pliers) near its probing end.
What is vertical distance between hotend and probe? When the nozzle touches the bed, what is height of the tip of the probe? It should be something between 1-1,5mm. If it is too high, the nozzle will hit the bed sooner than the probe can "see" calibration point.
Re: Hot-End/Bed Collision - Z axis travel problem?
Thanks David, the probe was working just fine - however, I followed your suggestion that I lower the probe and having done that, the calibration procedure is currently running OK! To achieve the 1.5mm I had to totally ignore the positional setting that was given in Joe's video and it is now about 3mm lower than it was!
I'll report back if all else goes well.
Re: Hot-End/Bed Collision - Z axis travel problem?
All looking pretty good so far. I used the 'live Z adjust' to get the correct performance of the test pattern. The figure was -1.8 which seemed a bit large but as the machine seems to be working OK, I have left well alone.
Thanks for your help with my problem.
Adrian
Re: Hot-End/Bed Collision - Z axis travel problem?
Adrian, one more question:
Are your trapezoid motor nuts in the Z axis installed in the correct direction? If they are upside-down then it's quite possible that it's never reaching it's maximum travel height due to the motor nut hitting the Z-stop too soon.