Random Grooves in Wood Carvings...Z axis Motor Tuning?


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Thread: Random Grooves in Wood Carvings...Z axis Motor Tuning?

  1. #1
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    Default Random Grooves in Wood Carvings...Z axis Motor Tuning?

    I have been working with my K2 50 X 50 for almost 3 years now, mainly debugging problems, making mistakes and breaking bits.

    But now that I am running out of original mistakes, I am getting down (hopefully) to the real craftsmanship involved.

    The attached images show a fourth axis (Tormach 6" rotary table) carving which is based on the digital sculpt by ZBrush artist Geert Melis. I use DeskProto CAM and it generated 12 million lines of G-code to carve the finish pass with a 1/32 new Amana tapered bit, at .0019 (I know, overkill) stepover. This is laminated basswood, about 1 foot tall.

    After a run that took the better part of two days, I was pleased that there appear to be only a few user initiated problems.

    But, there are a number of tiny incised horizontal lines around the A axis. I am guessing that the depth is about 1/1000 lower than either side of the groove.

    I am also guessing that the problem is with the servo driven Z axis on a ball screw. I have seen this artifact on regular 3 axis pieces, and on different woods.

    I use Mach 3, and have noticed that the fourth decimal digit jumps in 5 digit increments. ..ie although the G code digit is 0-9, the DRO will only show digits 5 units apart, like 0 and 5, and later during the same run 1 and 6 , 2 and 7 etc. I suspect that when I get a round down pass between two round up passes, the groove results.

    The Mach steps per unit calibration tool results in the intuitive 2029.1968996459 setting per. The ball screw and nut were replaced a while ago by a competent (I thought) machinist.

    I know that when I up the steps per, I can get full resolution, but the dimensions are all messed up. I wonder if this could be adjusted maybe in the post processor settings. I would need some help with this.

    Sand paper as a fix won't work where there are extremely fine details like muscle striations perpendicular to the groove.

    Suggestions please. My wife has suggested stamp collecting.

    Many thanks in advance.

    Mitchell T.

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    Attached Thumbnails Attached Thumbnails Random Grooves in Wood Carvings...Z axis Motor Tuning?-img_8569-jpg   Random Grooves in Wood Carvings...Z axis Motor Tuning?-img_8573-jpg   Random Grooves in Wood Carvings...Z axis Motor Tuning?-img_8575-jpg  
    Last edited by MitchellT; 05-23-2017 at 02:15 PM. Reason: inadvertent incomplete post


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    Default Re: Random Grooves in Wood Carvings...Z axis Motor Tuning?

    My guess would be a loose coupling on the ballscrew or motor. Anything else would likely result in a "shift" where the position was lost. It looks like what would happen if a coupler slipped a little in one direction, then slipped back. Check all of your set screws and make sure they are tight. If it's something else, it's much more difficult to troubleshoot.


    I use Mach 3, and have noticed that the fourth decimal digit jumps in 5 digit increments. ..ie although the G code digit is 0-9, the DRO will only show digits 5 units apart, like 0 and 5, and later during the same run 1 and 6 , 2 and 7 etc. I suspect that when I get a round down pass between two round up passes, the groove results.
    Only the display is rounded. Mach3 does not round the actual position that it keeps internally.

    If your steps per unit result in accurate distances traveled, then you don't want to change it.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

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

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


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Random Grooves in Wood Carvings...Z axis Motor Tuning?

Random Grooves in Wood Carvings...Z axis Motor Tuning?