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  1. #1
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    Mar 2020
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    mach3 constant velocity

    I'm struggling with shapes being overly rounded with constant velocity on, I'm trying to tweak CV "dist tolerance" and "stop cv on angle" settings but its not having any effect,

    This happens only on occasion and strangely in this instance the part comes out fine when machined with 1/4" tool but curved with half inch tool. If I uncheck CV with the half inch tool then it comes out ok but takes forever.

    By default the CV settings were dist tolerance 1 and stop cv on angle > 90... I tried dist tolerance 25 and stop cv on angle > 45 (based on things I saw online). It made no difference, I don't fully understand the meaning of these settings so I'm not too keen on playing around with them too much.

    I'm thinking is it possible that this has to do with the faster feedrate of the half inch tool, then the acceleration and deceleration would have more of an impact on the final shape?

    In the image added I drew a blue line to show the shape I'm supposed to get and if you look at the actual result you can clearly see how it actually gradually tapers down into an oval shape.

  2. #2
    Community Moderator ger21's Avatar
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    Mar 2003
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    35095

    Re: mach3 constant velocity

    Mach3's CV mode (and trajectory planner) is severely flawed. Especially when 3D cutting.

    CV mode's purpose, is to try to maintain the commanded feedrate (constant velocity). It does this pretty well.
    The problem is that accuracy goes out the window, and none of the controls that should help control accuracy work all that well.
    The best option is to increase acceleration as high as possible, if you're machine has the power to do so. Higher acceleration allows the machine to follow the path closer when directions change.

    The second best option is to slow down, which has the same affect as increasing acceleration.

    Even when you get it cutting really good, there are bugs in the planner that can result in small, random gouges in your parts.


    A friend of mine makes small, precise wood parts, and could not get Mach3 to give acceptable results. He switched to UCCNC, and got better quality parts, 30% faster.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  3. #3
    Member
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    Mar 2020
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    Quote Originally Posted by ger21 View Post
    Mach3's CV mode (and trajectory planner) is severely flawed. Especially when 3D cutting.

    CV mode's purpose, is to try to maintain the commanded feedrate (constant velocity). It does this pretty well.
    The problem is that accuracy goes out the window, and none of the controls that should help control accuracy work all that well.
    The best option is to increase acceleration as high as possible, if you're machine has the power to do so. Higher acceleration allows the machine to follow the path closer when directions change.

    The second best option is to slow down, which has the same affect as increasing acceleration.

    Even when you get it cutting really good, there are bugs in the planner that can result in small, random gouges in your parts.


    A friend of mine makes small, precise wood parts, and could not get Mach3 to give acceptable results. He switched to UCCNC, and got better quality parts, 30% faster.

    Ah I see that's kind of unfortunate. So does the distance tolerance unit control acceleration or is that something different?

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