Mechanical switch for tool length



  • Hi,

    I am really happy that I upgraded from Arduino+Ramps system to Duet.

    Now I want to add mechanical (micro)switch to my printer. The switch that one have in CNC machine to measure tool length.
    We print different materials, from PLA to Filaflex and etc... Flexible material we mainly we print with 0.8mm and PLA with 0.4mm nozzel for that we just exchange hotend with fins. Because of it, it happens that height of tool isn't exactly same and we would like to add mechanical switch which can be used to set exact height between bed and nozzle.
    Printer may travel to this switch before every print so that everything works safely.

    Is it some how possible to do that?

    Thanks.




  • administrators

    @kashyap said in Mechanical switch for tool length:

    Hi,

    I am really happy that I upgraded from Arduino+Ramps system to Duet.

    Now I want to add mechanical (micro)switch to my printer. The switch that one have in CNC machine to measure tool length.
    We print different materials, from PLA to Filaflex and etc... Flexible material we mainly we print with 0.8mm and PLA with 0.4mm nozzel for that we just exchange hotend with fins. Because of it, it happens that height of tool isn't exactly same and we would like to add mechanical switch which can be used to set exact height between bed and nozzle.
    Printer may travel to this switch before every print so that everything works safely.

    Is it some how possible to do that?

    That's the CNC equivalent of using a Z probe in a 3D printer, except that the Z probe is used at only one XY position (i.e. where the switch is). See https://duet3d.dozuki.com/Wiki/Connecting_a_Z_probe. Also see the description of M558 and G30 in the GCode wiki page.



  • I am curious how people manage to measure their nozzle Z with piezos, etc. My nozzles always have some filament oozing from them. They never seem clean enough to get an accurate measurement. Instead I measure the thickness of a line of extrusion. That also takes into account the fact that pressure extruding viscous plastics like ABS is enough to lift the nozzle / force the bed downwards on most of my machines. It also is done with everything at full working temperature as nozzles get hotter and beds higher as they expand.

    Do people measure with the nozzle hot, or cold?



  • @kashyap This is in fact what I have done. That is to say, I use a precision positioning switch for homing Z. In my case, I have built a hot end mounting arrangement that allows some movement in the Z directions but none in the X or Y directions. The nozzle itself acts as a probe. The switch is positioned such that when the bed is raised and touches the nozzle, the mount moves upwards and triggers the switch. The distance between the switch triggering and the nozzle touching the bed is about 0.3mm and this is set as the z offset.

    Wiring is simple as it is just a switch. The mechanics are a bit more involved as the hot end must be constrained from any movement in the X and Y directions, but free to move (against a spring) in the Z direction.

    Details of the mechanical arrangement can be found on my blog here https://somei3deas.wordpress.com/my-corexy-printer-build/

    and details of how to set it up on the Duet can be found here https://somei3deas.wordpress.com/2017/03/21/setting-up-a-metrol-positioning-switch/

    It was installed in February 2017 and has been running faultlessly ever since. Once the offset has been established, there is never any need to use baby stepping or any other method to alter the first layer.



  • @nophead See my post above. I don't use a piezo but a precision mechanical switch instead. But I do use the nozzle as probe. I find that heating the the nozzle to 140 deg C works fine. The nozzle moves against a spring so it takes a bit of force - not much but enough so that softened plastic always gets "squashed" and the trigger height is always consistent and repeatable.


  • administrators

    @nophead said in Mechanical switch for tool length:

    I am curious how people manage to measure their nozzle Z with piezos, etc. My nozzles always have some filament oozing from them. They never seem clean enough to get an accurate measurement. Instead I measure the thickness of a line of extrusion. That also takes into account the fact that pressure extruding viscous plastics like ABS is enough to lift the nozzle / force the bed downwards on most of my machines. It also is done with everything at full working temperature as nozzles get hotter and beds higher as they expand.

    Do people measure with the nozzle hot, or cold?

    I use the Smart Effector, and I measure with the nozzle at 190C. One issue is that when probing, the nozzle tends to leave small dots of filament on the bed. I clean these off before probing.



  • If the oozing plastic touches the bed first to make the dot how do you decide when the nozzle has struck, if indeed it does actually touch? I imagine with ABS it would take near infinite force to press it infinitely thin.



  • @nophead I can't speak for user of piezos but in my case, the "dot" only gets formed after the oozed filament has cooled. So during homing with the nozzle heated, any oozing filament would get pushed out sideways or back up inside the nozzle I imagine.



  • @dc42 said in Mechanical switch for tool length:

    @nophead said in Mechanical switch for tool length:

    I am curious how people manage to measure their nozzle Z with piezos, etc. My nozzles always have some filament oozing from them. They never seem clean enough to get an accurate measurement. Instead I measure the thickness of a line of extrusion. That also takes into account the fact that pressure extruding viscous plastics like ABS is enough to lift the nozzle / force the bed downwards on most of my machines. It also is done with everything at full working temperature as nozzles get hotter and beds higher as they expand.

    Do people measure with the nozzle hot, or cold?

    I use the Smart Effector, and I measure with the nozzle at 190C. One issue is that when probing, the nozzle tends to leave small dots of filament on the bed. I clean these off before probing.

    Ditto.

    Works great.



  • Thank you guys for the comments and your ideas.

    For oozing before Z calibration I am planning to Install brush like in Makerbot. But I don't know how effective will it be.

    @deckingman I will check your page as I would also like to use mechanical switch.

    I will update as soon as I have modified my printer.


 

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