Is my new CNC faulty?


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Thread: Is my new CNC faulty?

  1. #1
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    Default Is my new CNC faulty?

    Hi folks,

    I'm new to CNC but not to woodworking or computers. I bought a new CNC machine a few weeks ago but have been having a few issues and I'm getting the feeling that the company who made it are trying to fob me off. I was hoping someone here could tell from my description if there is a high chance of a hardware fault?

    Here are the issues.

    I have designs made from vectric software which has toolpaths saved as v carve for mach3 mm gcode.

    If I run a very basic gcode program to cut a small square for example the results appear ok.
    If I run a 10cm x 5cm sized program with two lines of text the machine cuts it as if the z axis isn't flush to the material. However I have surfaced both the scrap board and in desperation the material too. I have tried cutting the same gcode 4 times and the results are identical. By the 3rd word the cutter isn't scratching the surface. I sent the company the same code to cut and theirs cut perfectly. They are saying that there is no hardware issue even though when I press goto home after it's cut that the cutter appears to be up to 1mm away from the set home position. To me it is as if there is a minor error that gets larger the longer mach3 is running.

    If I cut a 10cm x 10cm square profile which is about 200 lines of code it appears ok but if I try cutting a text engraving of a similar size it turns out to be about 5000 code and that's when the machine starts cutting ok but then appears just to cut fresh air. I'm happy the z axis is flush to the material. Is this backlash or some other issue. This was hand made and I'm getting quite frustrated so Any help is appreciated.
    Thanks

    Sent from my SM-G935F using Tapatalk

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  2. #2
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    Default Re: Is my new CNC faulty?

    It sounds like your Z axis is losing steps on the plunge. When it's pushing into the material, it's trying too hard (or the material's too hard) and so, while the computer assumes it's reached the commanded position, it's actually higher than that. When the tool retracts, it goes to a higher position than it should, so you get the impression it's gradually drifting upwards. To fix that, adjust the acceleration in Motor Tuning - cut it in half, and see if things work better.

    If the behavior keeps happening, then it could be slippage of some kind. Either the tool itself is retreating into the collet or the coupler that's pushing the Z axis screw is slipping on its setscrew. Use a marker to check these things - make a mark across the coupler and the motor shaft, the coupler and the screw, and across the tool, just under where it goes into the collet. If things move, the marks will show it.

    Andrew Werby
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    Default Re: Is my new CNC faulty?

    Quote Originally Posted by awerby View Post
    It sounds like your Z axis is losing steps on the plunge. When it's pushing into the material, it's trying too hard (or the material's too hard) and so, while the computer assumes it's reached the commanded position, it's actually higher than that. When the tool retracts, it goes to a higher position than it should, so you get the impression it's gradually drifting upwards. To fix that, adjust the acceleration in Motor Tuning - cut it in half, and see if things work better.

    If the behavior keeps happening, then it could be slippage of some kind. Either the tool itself is retreating into the collet or the coupler that's pushing the Z axis screw is slipping on its setscrew. Use a marker to check these things - make a mark across the coupler and the motor shaft, the coupler and the screw, and across the tool, just under where it goes into the collet. If things move, the marks will show it.
    Thank you. I will definitely try that! Much appreciated.

    Sent from my SM-G935F using Tapatalk



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    Default Re: Is my new CNC faulty?

    Thinking about the cutter slipping idea. I cut the piece 4 times. If it had been slipping then I would have expected the cutter to have disappeared into the collet by the forth time. Every time I cut the piece it stopped scratching the material at exactly the same word every time. This must mean something.

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    Default Re: Is my new CNC faulty?

    Could this be backlash?

    Sent from my SM-G935F using Tapatalk



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    Default Re: Is my new CNC faulty?

    No that is not how backlash works. It is most likely what has already been mentioned. Either a loose coupler on z or losing steps. First try lowering z acceleration in mach 3 by half. See if it helps. If not check the coupler.

    Ben

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    Default Re: Is my new CNC faulty?

    To fix the coupler is it just a case of tightening up all bolts?

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    Default Re: Is my new CNC faulty?

    Most likely set screws or bolts yes.

    Ben

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    Default Re: Is my new CNC faulty?

    Quote Originally Posted by bhurts View Post
    Most likely set screws or bolts yes.

    Ben

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    Cheers Ben I'll give it a go.

    Sent from my SM-G935F using Tapatalk



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    Default Re: Is my new CNC faulty?

    Often if a set screw is slipping, merely tightening it further won't help. A screw can cut a groove in the shaft that just gets worse if it's tighter. It's better to remove the coupling (which can be quite difficult if the screw has galled the shaft) then grind a flat on the shaft where the setscrew hits and reassemble.

    Andrew Werby
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    Default Re: Is my new CNC faulty?

    Hmm ok. I'm going to try all this Thursday. Cheers

    Sent from my SM-G935F using Tapatalk



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    Default Re: Is my new CNC faulty?

    Well I've gone around the bolts on the z axis and all were quite tight. The two parts of the coupling appear close like the others so appear ok. I've cut the piece again and the cutter does not appear to move into the collet. And yet by the 4th word it is barely scratching the wood.

    Sent from my SM-G935F using Tapatalk



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Is my new CNC faulty?
Is my new CNC faulty?