Z axis calibration fail  

Re: Z axis calibration fail

Hi Christian,
can we see a picture of the printer please?

see if we can notice anything odd?

Joan

Re: Z axis calibration fail

I have just finished upgrading a friend's printer to a Mk2.5 which has the same Pinda and heatbed as a Mk3 and I, also, had a problem with XYZ calibration. I am in the process of writing the solution up as I think the problem is a design issue with the heatbed. But my experiance may help you now so I'll put in my 2 cents.

My problem was that the probes did not find the third calibration point in the right rear. The first two were fine but the third got it confused. Occasionally it would "find" the third point and continue on to the fourth and only then report failure.

Here's how you can tell if your failure is similar to mine:

If it stops at the third point then that's a sure way of telling. That's what happened to me most frequently.

If you watch carefully during the first two points you will see the Pinda search in a circular patter for the calibration point, the head going lower each time. Once it detects the point it does a "raster" (back and forth) search getting a better location. Finally it homes in on the point, going from the center of the point to the edge repeatedly. This last action tells you exactly where it thinks the calibration point is. In my failures it either failed to find it during the raster search and stopped right there, or it had a false detection of the point and the fine search was centered NOT on the printed calibration spot but somewhere about a cm away. Then it would continue to the fourth spot, which it detected fine but then would give the cryptic "calibration failed" message.

A video of one failure is here:

My "fix" was to use a small (1/4") metal disk (0.25mm thick) stuck to the bed at the third calibration point. I used some wax to temporarily stick it there which worked. Then it must be removed to do the final height calibration. Here's the video of it working:

As I siad before, I think this is a design flaw in the heatbed. The area around the third calibration point is too "noisy" for it to reliably find the right spot.

Hope that helps,

Bill W

Re: Z axis calibration fail

Pictures attached (hope this works 🙂

After exiting the wizard, the printer displays z-axis: 5 (???)

Re: Z axis calibration fail

screenshot

Re: Z axis calibration fail

That Pinder is way too high or sure looks that way in the picture.

Your Z is most likely failing because the pinder probe isn't detecting what it should - this is because the pinder isn't working or isn't adjusted properly.

Is the top of the pinder illuminated when powered ? are you sure it is connected in the correct place near the top at the far right in step 30 here

http://manual.prusa3d.com/Guide/8.+Electronics+assembly/513?lang=en

Also you can't do Pinder height using hit and miss methods. It needs to be set when the nozzle touches the bed with the metal plate on (best done manually turning the Z screws manually) the pinder should sit on top of one of the tie wraps (as per the build instruction) with a slight resistance, yes the pinder can be hard to move but make sure the clamp is slack and open the slot a little - and I do mean a little to let the pinder move. Press the pinder probe onto the tie wrap and you're in the ball park needed, tighten it up - doesn't need much tightening. I do this setting with the pinder over the beds centre and then check in a couple of other places.

http://manual.prusa3d.com/Guide/9.+Preflight+check/514?lang=en

You're looking for a 1mm gap between pinder and metal sheet when the probe is touching the sheet - do not move the bed when the probe is in contact with it and don't force the nozzle into the bed.

It doesn't really matter whether you set the pinder height with or without the metal sheet - the height doesn't care what surface it is measured from.

Re: Z axis calibration fail

The "Z 5" just means that the head is 5mm above the bed. At that stage it's not really meaningful.

If you watch the calibration at each point does the Pinda circle then zero-in on each printed calibration circle correctly or, as in my case, it zeroes in on a spot slightly (~1 cm) off of the circle on the third calibration point? First it does looping circles, then back and forth then it should zero right in on the circle, going from the center to the edge repeatedly. If that's not right over the circle then it has not found the correct spot. This was my problem for the third calibration point. It either didn't find it at all or found a false spot and failed at the end.

Re: Z axis calibration fail

Your extruder is completely misaligned, hotend should sit much higher up.
Dismantle the extruder and build it according to the manual.

Re: Z axis calibration fail

Well spotted - there is far too much thermistor showing below the bracket - mines approx 10mm if that below the clamp, shouldn't be able to see the nozzle as much either below the fan duct

Re: Z axis calibration fail

Hi Cristian,
your
extruder cold end heatsink is not located in the proper retaining slot
so it's too low

which messes up the Z distance

you will also need to readjust the Pinda

regards Joan

Re: Z axis calibration fail

Thank you all,

this was indeed the error.

Currently fiddling with the first layer adjustment (I think it is almost there now).

Again thanks for the professional advice given 🙂 🙂 🙂

Christian

Re: Z axis calibration fail

I have noticed the rug underneath your printer which may cause these problems.
In my case I have layed it down on two "same height" tables next to each other and it caused bending of the bed.
Conclusion: lay it on flat, solid, leveled surface.