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IndustryArena Forum > MetalWorking > MetalWork Discussion > is this a backlash problem?
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  1. #1
    Join Date
    Jan 2009
    Posts
    77

    is this a backlash problem?

    My gantry router is working great except one problem. When I route a square, the corners are not square. The straight sections are good but when I approach the corner there is a bump out.

    I'm not sure if it is a backlash problem or flexing in the router bit. I don't think it is a backlash problem because when I mill a circle it is perfect.

    I'm using a Bosch Colt router with a 1/4" spiral bit. I've tried slowing down my feed rate to 20ipm and depth of cut of 0.1". The problem still show up.

    Here is a drawing what the corners look like. You do you guys think?
    Attached Thumbnails Attached Thumbnails corner.bmp  

  2. #2
    Join Date
    Mar 2005
    Posts
    1673
    Hi,

    What CAM are you using?

    Looks to me as if you have “over cut corners” or some thing similar set.

    John

  3. #3
    Join Date
    Oct 2005
    Posts
    251
    I think you have a a programming issue. Can you post the code for review?

  4. #4
    Join Date
    Jan 2009
    Posts
    77
    I'm using the wizard in mach3.

    I've also drawn a square in autocad, used flashcut to generate g-code, and then use mach3 to control the machine.

  5. #5
    Join Date
    Feb 2007
    Posts
    505

    Cool

    oups

  6. #6
    Join Date
    Jan 2009
    Posts
    77
    I did use the wizard in mach3. That is when I noticed the problem. Then I tried the autocad route.

  7. #7
    Join Date
    Apr 2009
    Posts
    3
    Can you try the same program with a larger dia bit, or possibly a bit with more flutes?

    I doubt it, but you may have a problem with the bit flexing. How heavy of a chip are you taking? For my 3 Onsrud routers I refuse to run a 2 flute 1/4" bit at anything faster than 18,000 rpm and 350ipm.

    I tend to want to see your code to see if your post may be kicking out something weird, your cut is not deep enought to really cause you a problem like this unless your spindle speed is way too low.

  8. #8
    Join Date
    Jan 2009
    Posts
    77
    here is my code.


    N10 G00 Z 0.10000
    N20 G00 X 0.00000 Y 0.00000
    N30 G01 Z-0.10000 F20.00
    N40 G01 X 1.00000 Y 0.00000 F50.00
    N50 G01 X 1.00000 Y 1.00000
    N60 G01 X 0.00000 Y 1.00000
    N70 G01 X 0.00000 Y 0.00000
    N80 G01 Z-0.20000 F20.00
    N90 G01 X 1.00000 Y 0.00000 F50.00
    N100 G01 X 1.00000 Y 1.00000
    N110 G01 X 0.00000 Y 1.00000
    N120 G01 X 0.00000 Y 0.00000
    N130 G01 Z-0.30000 F20.00
    N140 G01 X 1.00000 Y 0.00000 F50.00
    N150 G01 X 1.00000 Y 1.00000
    N160 G01 X 0.00000 Y 1.00000
    N170 G01 X 0.00000 Y 0.00000
    N180 G01 Z-0.40000 F20.00
    N190 G01 X 1.00000 Y 0.00000 F50.00
    N200 G01 X 1.00000 Y 1.00000
    N210 G01 X 0.00000 Y 1.00000
    N220 G01 X 0.00000 Y 0.00000
    N230 G01 Z-0.50000 F20.00
    N240 G01 X 1.00000 Y 0.00000 F50.00
    N250 G01 X 1.00000 Y 1.00000
    N260 G01 X 0.00000 Y 1.00000
    N270 G01 X 0.00000 Y 0.00000
    N280 G01 Z-0.60000 F20.00
    N290 G01 X 1.00000 Y 0.00000 F50.00
    N300 G01 X 1.00000 Y 1.00000
    N310 G01 X 0.00000 Y 1.00000
    N320 G01 X 0.00000 Y 0.00000
    N330 G01 Z-0.70000 F20.00
    N340 G01 X 1.00000 Y 0.00000 F50.00
    N350 G01 X 1.00000 Y 1.00000
    N360 G01 X 0.00000 Y 1.00000
    N370 G01 X 0.00000 Y 0.00000
    N380 G01 Z-0.73000 F20.00
    N390 G01 X 1.00000 Y 0.00000 F50.00
    N400 G01 X 1.00000 Y 1.00000
    N410 G01 X 0.00000 Y 1.00000
    N420 G01 X 0.00000 Y 0.00000
    N430 G00 Z 0.10000


    I'm using 1/4", 2 flute, at 18000 rpm in MDF. I'll try running at a higher RPM later.

  9. #9
    Join Date
    Mar 2006
    Posts
    474
    Well, it's not a programming issue, you aren't cutting radiuses on your corners.

  10. #10
    Join Date
    Mar 2005
    Posts
    1673
    Are you using “constant velocity” or “exact stop” in Mach? Not sure if this could be the problem but if you have CV set try switching to ES.

    What are you using for anti backlash nuts, if there your own design do you have a picture?

    John

  11. #11
    Join Date
    Jan 2009
    Posts
    77
    i'm using anti-backlash nut made by Zycon. Here is a picture. The mach is set to CV.

    What is the difference between CV and ES?

    thanks
    Attached Thumbnails Attached Thumbnails Lead_Nut(t).jpg  

  12. #12
    Join Date
    Mar 2005
    Posts
    1673

  13. #13
    Join Date
    Mar 2005
    Posts
    1673
    Does it do the same thing on all four corners?

    Are you using stepper or servos?

  14. #14
    Join Date
    Jan 2009
    Posts
    77
    Quote Originally Posted by Oldmanandhistoy View Post
    Does it do the same thing on all four corners?

    Are you using stepper or servos?
    it happens on all corners, I'm using stepper motors.

    I'll have to play around with CV settings.

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