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Thread: Can not cut circle

  1. #1
    Join Date
    Apr 1999
    Location
    Rock Hill SC
    Posts
    478

    Default Can not cut circle

    My BT48 will not cut a round circle. I have tried all of the usual things, pinions, adjustments, etc. Even replaced the X axis pinion just for drill.

    Recently I was cutting a circle in Corian. The first pass the bit ran smoothly around the circle. On the second pass and all those after that the bit jerks and makes lumpy parts to the circle. It always does this in the same places so that the pieces are very nicely cut out, just not the right shape.

    I am just about to decide that the problem is in the software rather than the machine.

    Has anyone else had this problem? I am kind of thinking of converting the machine to a rezurection control system but if I did I would like to use Mach 3 as my operating system. Any comments on that?

  2. #2
    Join Date
    Jan 2004
    Location
    iBILD Solutions - Southern NJ
    Posts
    7,965

    Default

    How fast and how deep are you cutting the Corian? Sounds to me like you are stalling and losing steps in the axis assigned to the moving table. Is this correct? Where is the deviation happening - in what direction?

    -B
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  3. #3
    Join Date
    Apr 2007
    Location
    Marquette, MI
    Posts
    3,376

    Default

    "I am just about to decide that the problem is in the software rather than the machine."

    That decision would be incorrect. My guess is that the lumps and bumps are near the 1/8 and/or 1/4 points of the circles where one motor (or the other) reverses direction. This is backlash. Assuming the gearboxes are OK, it will be 1) rack to pinion adjustments 2) Z slide or lower Y car Vroller adjustments
    Gary Campbell
    GCnC Control
    GCnC411(at)gmail(dot)com
    ShopBot Controller Upgrades
    http://www.youtube.com/user/Islaww1


    "We can not solve our problems with the same level of thinking that created them"
    Albert Einstein


  4. #4
    Join Date
    Apr 1999
    Location
    Rock Hill SC
    Posts
    478

    Default

    Quote Originally Posted by Gary Campbell View Post
    "I am just about to decide that the problem is in the software rather than the machine."

    That decision would be incorrect. My guess is that the lumps and bumps are near the 1/8 and/or 1/4 points of the circles where one motor (or the other) reverses direction. This is backlash. Assuming the gearboxes are OK, it will be 1) rack to pinion adjustments 2) Z slide or lower Y car Vroller adjustments
    You called it! The lumps are right at that point. I will check as you suggested.

    Guess I am gonna have to think up a better reason to but that box from you.

  5. #5
    Join Date
    Mar 2014
    Location
    Lake Tahoe CA
    Posts
    19

    Default

    Quote Originally Posted by tlempicke View Post
    You called it! The lumps are right at that point. I will check as you suggested.

    Guess I am gonna have to think up a better reason to but that box from you.

    Did you get the issue fixed? I'm currently experiencing the same circle issue. Ordering new pinions tomorrow, it's been 5 years with the factory pinions. I am curious how your situation ended though...

  6. #6
    Join Date
    Apr 1999
    Location
    Rock Hill SC
    Posts
    478

    Default

    Actually yes I have.

    I put new motors on the machine and converted it to a Centroid controller. The difference in accuracy is remarkable. When one part needs to fit into another I use a clearance of .025 to .030 and get a good fit each and every time. All of the hand work that I used to do is for the most part gone.

    It has taken a lot of the challenge and mystery out of the experience, but then I have teen age grand children that manage to take up the slack.

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