Z calibration revisited  

Z calibration revisited

This is a continuation of my original thread " Calibration failed". I started a new thread to save you a long read. I got another intractable clog, and took down my hot end again. On reassembly I once again got the calibration error.. "check axes and try again." This time my messing around with the Z axis did not work. So I thought some more. Calibrate XYZ starts with calibrating Z. So how does the device' s teinsy brain know where the head is in Z. It certainly does, as it displays the value. The stepper can count turns, but it must do so from a sensed Zero. This is provided by the PINDA sensing the bed. So calibrate Z should start by the head going down until the PInda sees the bed . Then it goes up to 5 mm. Now suppose the PINDA is stuck on " yes I sense the bed" . The head does not go down and keeps going up, because there is never a signal " Now I don't sense the bed". It keeps going up
until it hits the top z stops and stops, showing Z = 5. The clue was a chance remark from St Joan of Halifax, " change in the red light is not enough to prove that the PINDA works .. you need to check via the end stop display" . I thought that my PINDA was intermittent when I assembled the machine but the machine worked. I think I fixed it in a working position, but it eventually failed. So I chatted , since PRUSA should have replaced the probe ( 5 month old machine). Chat was so slow that I could do a sudoku between replies, and wanted pictures and movies. I realized that if, in my conceit I value my time at minimum wage, I would save by just buying one, which I did, and it worked. I learned a second lesson also. X calibration will fail at the first point of 4 if the head does not go close enough to the left side of the X axis. You need to see just about Zero of the shiny smooth rod at the left end. In my case I just needed to tuck in the left sided fan wires better. I redid the cable wrap for the PINDA wire. I may be approaching half of my ZIP tie supply.! 🙂