preferred design for tool changing mating plate



  • i am almost done with my independent tool changing corexy printer. right now, i am using a plate with 4 spheres on the x carriage that mates with 4 circular recesses on the tool to be picked up. my tolerance is in the 0.2-0.3 mm in either x or y when measuring the nozzle position with a camera in terms of repeatability. I am not totally happy with this.

    my question is:
    would having just 3 points such as in the E3D that uses thorlabs mating plates be better than 4?

    i do intend to use metal pins instead once I can finally test it out and see if it works the way it is. perhaps even using electromagnets instead of permanent magnets. right now, it need to change direction to park and pick up the tool.

    the extruder i am using is the titan extruder. would it be best to attach the plate to the extruder/motor (the top part) or somewhere closer to the nozzle (down at the bottom)?



  • A three legged stool can not rock, no matter how bad the surface it's sitting on. It is perfectly stable.

    Otoh, a 4 legged stool must have perfect length legs on a perfectly flat surface to avoid rocking unless the stool flexes considerably.



  • @tenaja that's what I figured too. I guess 3 legged stool it is!



  • @tekstyle said in preferred design for tool changing mating plate:

    would having just 3 points such as in the E3D that uses thorlabs mating plates be better than 4?

    YES

    Four is what is known as "over constrained" which leads to innacuracies and non-repeatability. Three is "exactly constrained" and will work a lot better.

    For more info, see this (somewhat expensive) book: https://www.amazon.com/gp/product/0791800857/

    I found it very worthwhile. And it is possible to rent that book.



  • @Danal thank you for the link to an awesome book!



  • Have you made any headway on this? I'd sure like to see what you came up with.

    If you have not finished, you might consider the E3D toolchanger design, or the Jubilee design. The latter is made to be compatible with the E3D, but with the added benefit of a torque clamp, rather than a position clamp. (Torque can compensate for wear.)



  • @tenaja
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    these are what i came up with. it uses a plate of magnets in alternating polarities turning the plate 30 degrees in either direction will couple or decouple the tool from the x carriage. i was inspired by the jubilee and the way it is assembled is based on it's design. however, instead of having a frame mounted motor, it uses a N22 gearbox motor driven by a servo module or a mini stepper motor. still a concept at this point.



  • Nice idea about using the geared locking mechanism. I've been struggling myself to work out how on earth to so something like this but keep it compact as soon as I add the motor with enough torque it's all of a sudden massive.



  • @tekstyle
    Thanks for sharing. I like your little worm gear motor idea a lot, especially if it can be compact enough so the extruder is not more wobbly.


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