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  1. #13

    Join Date
    Jun 2018
    Posts
    106

    Re: Horrible Surface Finish

    Have you verified the ballscrew is running true . Also , have you tried to conventional mill your finish pass

  2. #14

    Join Date
    Jun 2018
    Posts
    31

    Re: Horrible Surface Finish

    I ran several diagnostic tests this morning using CamBam and Fusion360 to generate gcode.

    For the first test I adjusted Arc Output to Convert to Lines and set Arc to Lines Tolerance to 0.001. The first two pictures are the results using CamBam code. The X and Y axis straight cuts are pristine. The angle cuts are OK but not as good as the straight line cuts. The radius cuts are worse showing more severe scalloping than the angle cuts.

    The second test used F360 code. Surprisingly the results were not as good as CamBam. See pictures 3 and 4. The straight cuts were very close to the CamBam results while the angle and radius surfaces were somewhat worse. For info I ran two tests using F360. The first test Radius Arcs was checked as "No" while the second test it was checked as "Yes". There was no discernible difference in the surface finish between the two tests.

    For info the tests were run using a new 3/8" 4-flute carbide end mill running at 450 sfm and .0018" CLPT. DOC was .500".

    I still believe it's a software issue but not sure where to go from here.

  3. #15

    Re: Horrible Surface Finish

    I think we need a bit more information about your machine. Model? Size? I assume you are using stepper motors? If so, maybe adjusting the micro-stepping a bit finer would help.
    Jim Dawson
    Sandy, Oregon, USA

  4. #16
    Registered
    Join Date
    Dec 2005
    Posts
    329

    Re: Horrible Surface Finish

    Can you redo your test with a shallower depth of cut? keep EVERYTHING elese the same?

  5. #17

    Join Date
    Jun 2018
    Posts
    31

    Re: Horrible Surface Finish

    Quote Originally Posted by metalmayhem View Post
    Have you verified the ballscrew is running true . Also , have you tried to conventional mill your finish pass
    I have not done a runout check on the ball screws nor tried conventional milling. Another test for tomorrow!

  6. #18

    Join Date
    Jun 2018
    Posts
    31

    Re: Horrible Surface Finish

    Quote Originally Posted by Jim Dawson View Post
    I think we need a bit more information about your machine. Model? Size? I assume you are using stepper motors? If so, maybe adjusting the micro-stepping a bit finer would help.
    My mill is a PM-932 conversion. It's a medium size benchtop mill weighing about 850 lbs. Table is 9 x 32". Yes, steppers on X and Y are 1600 oz in and Z is 4200 oz in. Current microstepping is set to 3200. I can set it to 6400 and see if that has an effect.

    - - - Updated - - -

    Quote Originally Posted by cncuser1 View Post
    Can you redo your test with a shallower depth of cut? keep EVERYTHING elese the same?
    Certainly can. I'll test it in the morning.

  7. #19
    Registered
    Join Date
    Jan 2005
    Posts
    1934

    Re: Horrible Surface Finish

    I would just hand write a G-code with a G3 to cut a circle and see what it looks like. If the faceting is still there then you know it is either the machine or the controller. and not a CAM problem.

  8. #20
    Registered
    Join Date
    May 2008
    Posts
    1157

    Re: Horrible Surface Finish

    I'm thinking bent ball screw or the end work is not centered.

    I know it sounds strange but loosen the bolts on the bearing support side of a screw and see if it gets better.

    It could be either end.

    I had a problem like that a few years ago. The end work was off center and the hole table would rock around and make waves in the cut. It got worse as you moved to the area with the bad end work.

    I did a video of it.

    https://www.youtube.com/watch?v=d3Gg7qDeFCY
    youtube videos of the G0704 under the name arizonavideo99

  9. #21
    Registered
    Join Date
    Jan 2005
    Posts
    1934

    Re: Horrible Surface Finish

    I'm thinking bent ball screw or the end work is not centered.
    I would think if this were the case that it would show up in straight cuts. For example if the X axis screw were bent then cuts using only X would show this, but according to the OP this isn't the case.

  10. #22

    Join Date
    Jun 2018
    Posts
    31

    Re: Horrible Surface Finish

    Quote Originally Posted by 109jb View Post
    I would just hand write a G-code with a G3 to cut a circle and see what it looks like. If the faceting is still there then you know it is either the machine or the controller. and not a CAM problem.
    Here's the F360 gcode I ran yesterday. It uses G2. Is this what you were thinking?

  11. #23
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    Join Date
    Dec 2005
    Posts
    329

    Re: Horrible Surface Finish

    Good suggestion.

  12. #24
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    Dec 2005
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    329

    Re: Horrible Surface Finish

    I'm no G code expert but I don't see a problem with your code. Arcs are programmed as arcs, not as a series of small straight lines.

    In my opinion it is not a software issue.

    You've done stiffness tests of the table, have you done similar for the head and spindle isolated(Does this machine have a quill)?

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