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Large Z dive when CNC pocketing

Discussion in 'CAM' started by sergiomajluf, Apr 4, 2021.

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  1. sergiomajluf

    sergiomajluf Well-Known
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    Hi everybody

    I'm getting weird hops in the z axis when doing pocket operations.

    For example, a 30mm deep pocket, with 3mm cut per path should generate 10 "layers", am I right? I'm getting only 4 layers, three 3mm deep, and then a fourth, 300mm deep.

    upload_2021-4-4_10-16-0.png

    Or a 6.73 deep cut ("base-pivotes" toolpath), with DoC of 2mm creates a first Z pass of -0.73, then correctly a -2.7mm pass and then incorrectly -6.7

    (on a side note, is it possible to make the first pass deeper so I can appropriately use a compression bit?)

    When doing shallow pockets it is not as noticeable, but it is still there. Have attached workspace for reference. All three toolpaths show the same behavior.
     

    Attached Files:

    #1 sergiomajluf, Apr 4, 2021
  2. David the swarfer

    David the swarfer OpenBuilds Team
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    smells like a classic floating point inequality Peter
     
    #2 David the swarfer, Apr 4, 2021
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  3. sharmstr

    sharmstr OpenBuilds Team
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    Peter will be able to answer this. But yes, I see the issues. However, if I select your 30mm pocket and add a new operation, it correctly gives me 10 cut layers. So maybe your toolpath got corrupted.

    G0 Z0
    G1 F400 Z-3.0000
    G1 F1200 X-35.4546 Y29.1279 Z-3.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-3.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-3.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-3.0000 S1000
    G1 F400 Z-6.0000
    G1 F1200 X-35.4546 Y29.1279 Z-6.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-6.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-6.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-6.0000 S1000
    G1 F400 Z-9.0000
    G1 F1200 X-35.4546 Y29.1279 Z-9.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-9.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-9.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-9.0000 S1000
    G1 F400 Z-12.0000
    G1 F1200 X-35.4546 Y29.1279 Z-12.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-12.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-12.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-12.0000 S1000
    G1 F400 Z-15.0000
    G1 F1200 X-35.4546 Y29.1279 Z-15.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-15.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-15.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-15.0000 S1000
    G1 F400 Z-18.0000
    G1 F1200 X-35.4546 Y29.1279 Z-18.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-18.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-18.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-18.0000 S1000
    G1 F400 Z-21.0000
    G1 F1200 X-35.4546 Y29.1279 Z-21.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-21.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-21.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-21.0000 S1000
    G1 F400 Z-24.0000
    G1 F1200 X-35.4546 Y29.1279 Z-24.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-24.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-24.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-24.0000 S1000
    G1 F400 Z-27.0000
    G1 F1200 X-35.4546 Y29.1279 Z-27.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-27.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-27.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-27.0000 S1000
    G1 F400 Z-30.0000
    G1 F1200 X-35.4546 Y29.1279 Z-30.0000 S1000
    G1 F1200 X-35.4546 Y27.3201 Z-30.0000 S1000
    G1 F1200 X28.2123 Y27.3201 Z-30.0000 S1000
    G1 F1200 X28.2123 Y29.1279 Z-30.0000 S1000
     
    #3 sharmstr, Apr 4, 2021
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  4. sharmstr

    sharmstr OpenBuilds Team
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    Forgot to say that you can set your first cut depth by entering a value in "Cut Depth Start" box. So, if you want to start at 6 and your cut per pass depth is 3 then set it to 3.
     
    #4 sharmstr, Apr 4, 2021
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  5. sergiomajluf

    sergiomajluf Well-Known
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    Thanks sharmstr. I started fresh and got a correct pocket toolpath for the 30mm. Then added a second toolpath for other geometry, always with whole numbers, and got the same error (don't know if whole vs decimal makes a difference then).

    I can still cnc the piece by trying to create new files for each operation still, but hopefully this apparent bug will be catched by the allmighty Peter :)

    happy easter sunday guys!
     
    #5 sergiomajluf, Apr 4, 2021
    sharmstr and Peter Van Der Walt like this.
  6. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Post the workspace exports so we can go bug hunting next week
     
    #6 Peter Van Der Walt, Apr 4, 2021
  7. sergiomajluf

    sergiomajluf Well-Known
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    Attached to first post. Thanks!
     
    #7 sergiomajluf, Apr 4, 2021
    Peter Van Der Walt likes this.
  8. sharmstr

    sharmstr OpenBuilds Team
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    I just tried to recreate your issue and cant. Clearly there's an issue with the workspace you posted, but any and all new toolpaths generate correctly even with 11.19 cut depth. Peter might need more info (exact steps, video, etc) in order to find the issue. I dunno.
     
    #8 sharmstr, Apr 4, 2021
    Peter Van Der Walt likes this.
  9. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Quick, not-at-work-bugfix pushed, give it a test (force a refresh with ctrl+F5/shift+F5) and let me know if that broke something else in turn, didn't do a lot of testing.
     
    #9 Peter Van Der Walt, Apr 4, 2021
  10. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Changing the geometry to unmerged on a pocket revealed a bug. I just cannot remember why the stepdown routine differed between merged and unmerged - was there a reason - or just forgot to update one of them at some point lol. Fixed bug with Z on pockets · OpenBuilds/OpenBuilds-CAM@f86c7cc anyway if it broke something else, his sample workspace works now with both merged geometry and without.
     
    #10 Peter Van Der Walt, Apr 4, 2021
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  11. sergiomajluf

    sergiomajluf Well-Known
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    Can confirm it works OK.
    THANKS!
     
    #11 sergiomajluf, Apr 5, 2021
    sharmstr and Peter Van Der Walt like this.

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