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Thread: Inconsistent cut dimensions on my workbee CNC

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    Member JoshieB's Avatar
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    Exclamation Inconsistent cut dimensions on my workbee CNC

    Hello! I have been working on this issue for a while and I can't seem to figure it out. I'm new to the CNC scene so this issue might be a walk in the park for an experienced person. Any help is appreciated

    I am trying to profile simple shapes to fit a silicone strip in the cut gap.
    the cut width is supposed to be 8mm with a depth of 3mm, but for some reason, the width varies between 7-7.8mm and reaches depths of 3.5-4mm (as presented in the octagon cut in the attached photo). The material I am using is a 6mm thick sheet of acrylic.
    the same issue occurs even when I'm using a much more forgiving material such as MDF.
    I am cutting with a 6mm o-flute (1/4"). I have attached the feeds and speeds at the bottom
    the machine is a 750x750 WorkBee desktop CNC, Nema23 2.8A motors, TB6600 stepper drivers, Arduino Uno, 12V 15A power supply, GRBL engine, Mekita RT0700C router
    i am using Cut2D

    I have tried:
    - slowing down the cut
    - using fresh endmills: seems to make a somewhat accurate cut for a short distance then the issue starts again
    - switched from a 3D printed spindle holder to a solid aluminium one
    - tightening the plastic axis wheels: they are very tight, is that a bad thing? there are also track marks on them I'm not sure if that's normal

    I really need help on this one

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    Default Re: Inconsistent cut dimensions on my workbee CNC

    With plastic wheels and a 12v power supply, it's surprising you're doing as well as you are. The plastic wheels mounted like that have very limited rigidity, and they sound like they're wearing out already. And that power supply will only let your NEMA 23s limp along; you're probably losing steps if you're going at that feedrate. After one of these part runs, does the tool come back to its previous zero points?

    Andrew Werby
    https://computersculpture.com/


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    Default Re: Inconsistent cut dimensions on my workbee CNC

    Quote Originally Posted by awerby View Post
    With plastic wheels and a 12v power supply, it's surprising you're doing as well as you are. The plastic wheels mounted like that have very limited rigidity, and they sound like they're wearing out already. And that power supply will only let your NEMA 23s limp along; you're probably losing steps if you're going at that feedrate. After one of these part runs, does the tool come back to its previous zero points?
    I have set limit switches and the machine homes after the cut so I can't tell for sure if it has lost steps, but you may be right about the feeble 12V 15A power supply. what power supply do you recommend i should switch to (judging by the parts used)



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    Default Re: Inconsistent cut dimensions on my workbee CNC

    Instead of telling it to "home", tell it to return to 0,0,0. If you know where that's supposed to be, that will show you where it thinks it is. You can calculate the optimum power supply if you know the inductance of your motors in Millihenries (Mh) The formula is: square root of the inductance times 32 equals optimum VDC input for best high-speed performance. Usually it's a lot higher than 12. The amperage rating is probably okay, though.

    Andrew Werby
    https://computersculpture.com/


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Inconsistent cut dimensions on my workbee CNC

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Inconsistent cut dimensions on my workbee CNC