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aviphysics

anyway to auto home z without smashing filament into hot end?

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It seems mildly problematic that the nozzle smashes itself directly into oozing filament during the z homing operation. I tried making it also jog along the x axis during the operation, but it only wants to move one axis at a time.

Anyone have an idea?

For the time being, I have been just reaching in and grabbing the filament, but I don't like doing this and sometime burn my fingers on the hot end.

 

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I do the same work-around for some months. And sometimes I miss the right time to grab the outflow with tweezers (better for the fingers).

Actually, it should be possible to solve the problem as all the involved actions are in the start.gcode.

So this order might solve the problem:

 

  • heat up the bed (if a heated bed is present)
  • zero the z axis
  • lower the bed by something like 10-15mm
  • heat up the hotend
  • move it a small amount in x or y direction
  • zero it again (in case you change the height manually)
  • and from there it goes...

 

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It's really not that much of an issue, especially when the head is hot,since the bed is sprung, and will deflect out of the way; it is a good idea to just grab the filament - I generally put a pause into my UM1 start gcode and right after the initial priming extrusion, to give me time to clean up the head with a pair of tweezers. Part of the standard process is actually intended to drag the oozing head over the bed specifically to clean it, on the way in to the start of the skirt.

What is potentially more of an issue is homing the z-axis before heating the head; you really do want any plastic attached to the head to be molten before you ram it into the print bed. Because of the springs, it's probably not a huge deal either way, but I always make sure to heat the head before homing the z-axis.

 

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[...]

What is potentially more of an issue is homing the z-axis before heating the head; you really do want any plastic attached to the head to be molten before you ram it into the print bed. Because of the springs, it's probably not a huge deal either way, but I always make sure to heat the head before homing the z-axis.

 

That's true!

I was assuming a clean head....

 

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I drilled a large half inch hole in my bed plate where the Z homes. So when my Z homes it homes into thin air and sometimes when it primes the filament goes through the hole to the area beneath.

On the negative side of this: I can't build a part that utilizes this spot on my built plate. Or if I do it will be bridging on the first layer.

 

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Another solution might be to mess with the "start gcode" settings. For example you can add a sleep (say 3 seconds) and/or a pause (where you have to push on the ulticontroller to continue). That gives you more time to not burn your fingers.

And while changing that code you might want to increase the E feed from 3 to 6mm of filament and decrease the speed by maybe 3X so you don't extrude to fast and potentially grind the filament.

 

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