UM3 extended Z axis print start errors

[burdickjp 6]

I have a UM3E which I've installed some buildtak print sheets on. I've turned off automatic leveling, as the nozzle would melt the print surface. This was behaving correctly for a long time, but recently it's started to misbehave.

 

At print starts it will drive the Z axis down past the end stop. Since it's lost its Z position it will then drive the nozzle into the bed.

 

When I turn on autoleveling and switch to a different bed material the startup sequence is a little different and it behaves normally.

 

I'd like to go back to buildtak sheets. They worked before.

 

Has anyone run into similar problems before? Any suggestions on fixes?

[Enigma_M4 101]

Hi,

it sounds a bit confusion, as moving past the Z end stop (lowering the bed to much) would normally result in to much space between print bed and printhead at start of print.

Your problem may result in the bed stopping before the Z end stop is reached.

So you should check the small pit where the Z end switch is located for debries blocking the Z switch.

Regards

[burdickjp 6]

1 minute ago, Enigma_M4 said:

moving past the Z end stop (lowering the bed to much) would normally result in to much space between print bed and printhead at start of print.

Your problem may result in the bed stopping before the Z end stop is reached.

So you should check the small pit where the Z end switch is located for debries blocking the Z switch.

Regards

 

If the machine tries to go past the bottom of the Z travel then the head to bed distance is shorter than the controller thinks, and it crashes the nozzle into the bed.

The bed is homing correctly during other operations, including print completion and automatic leveling.

 

[Enigma_M4 101]

15 minutes ago, burdickjp said:

If the machine tries to go past the bottom of the Z travel then the head to bed distance is shorter than the controller thinks

I'm sorry to say so, but you're wrong. If the distance between lowered bed and head is shorter than the controller thinks (which means, shorter than it should be), the bed hasn't lowered enough, it didn't lower too much.

Check the Z switch as suggested, as it's easily be done, also check, if the Z enstop works at all (in systems menu).

[burdickjp 6]

Just now, Enigma_M4 said:

I'm sorry to say so, but you're wrong. If the distance between lowered bed and head is shorter than the controller thinks (which means, shorter than it should be), the bed hasn't lowered enough, it didn't lower too much.

Check the Z switch as suggested, as it's easily be done, also check, if the Z enstop works at all (in systems menu).

 

If the bed is driven past the bottom of its travel then the Z axis stepper motor stalls and skips steps. The controller thinks it kept moving. The mechanical distance between the bed and nozzle is less than the controller thinks.

[Enigma_M4 101]

If you think so ....

I'm out.

[burdickjp 6]

All end stops are working according to the systems menu.

[Josnoww 15]

Hi @burdickjp

 

I am sorry to hear you are experiencing problems with your printer. From the information you provided it is difficult to determine what exactly causes the problem with your printer. 

 

One thing you could try is to check the Z- limit switch for debris. It very rarely happens, but it is possible for debris from previous prints (prime blobs, or other little parts of extrusion) to make their way into hole where the Z switch is located. This can cause the homing to fail or home to an inconsistent position. Which could lead to the behaviour you are describing.

 

To check for debris you need to raise the bed and find the limit switch location. On the UM3 it is located in a hole to the left of the Z-spindle. From experience I can say that it is quite difficult to feel any debris by manually pressing the switch. So I would recommend doing a good visual inspection. It can be quite difficult to reach and see at the same time, but with a phone and a flashlight you can get quite a long way.

 

I hope this helps for you. If not please let me know, then I will see what else we can try! :-)