Layer change in 2 steps (overshooting-reducing)



  • Hi

    Is it possible to set the firmware to do the Z movement in 2 steps - first overshooting and then going to the target position?

    Let's say the layer height is 0,3mm. The bed would lower for example 1mm and then go up 0,7 to produce the layer change of 0,3mm.

    This might help in some cases (like mine) where the layer height is inconsistent especially with Z hop due to more complicated than usual mechanics on Z.

    Thanks!


  • administrators

    Can you fix this with Z hop on layer change?



  • Are you saying your Z axis doesn't move exactly as called for? It could be backlash in the Z axis, meaning if you move up 1mm and then back down 1mm it doesn't really come back to the original start point?

    I think there are backlash parameters you can adjust in Duet but I'm not 100% sure. Maybe someone will chime in on this?



  • Z hop on layer change, something that the slicer (Cura in my case) would offer? Can't see that option in Cura 2.7.

    My huge bed does not move accurately. Most of the issues come probably from the "homemade" GT2 belt (closed from an open belt) that joins the rods on the corners of the bed to one motor. Have had like 10 different approaches on that. Looks now that I have to go back in the initial idea of motor per rod (4 total).



  • What have you tried using to close the belt?



  • The loop is closed with a piece of the same belt, teeth sanded down and every 8 corners of the two pieces (belt and connector strip) slightly chamfered for them not to poke anything. The connection is glued with Loctite's gel glue (tried several and the best results so far are with consumer grade "Super Glue 3", brush bottle).

    The earlier iterations were failing probably due to the added thickness of the belt in the connection, since when the connected section was turning around any of the pulleys the layer height got a lot higher (yes, higher, faster movement in Z, no slippage). The trick to solve this was to join the ends when wrapping them around the same size pulley as in the ends of the Z rods producing one ugly curly joint in the belt but that did not cause weirdness when in contact with the pulleys. When gluing straight (using another strip of belt as a positioner) the prementioned problem occured - the longer the joint the more fat layers. And ofcourse when trying to make as short of a connection as possible the probability for it to snap mid print raised.

    Maybe somebody finds this helpful if considering belt joining (just put 4 motors instead of the belt)


  • administrators

    Regarding z hop on layer change, from memory you can contact figure slicers to retract on layer change, and zhop on retract… So that might work. Also I believe some slicers have layer change scripts that you could customise.

    It does sound though that it's a mechanical issue that really needs sorting.



  • Oh yes, retract on layer change. That would do it.

    Now running the printer with the new belt without issues (so far).


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