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Uncategorised WoodWorking Machines > My homemade CNC router cant cut holes as it should? Anyone know what can be wrong??
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  1. #1
    Join Date
    Aug 2003
    Posts
    72

    My homemade CNC router cant cut holes as it should? Anyone know what can be wrong??

    Hi all.
    A couple of years ago I built a large homemade CNC machine. It has served me well but one thing is not going as it should with it. I cant cut holes in the right shape. It has a quit heavy gauntry and Maybe that is the cause but think I need some help with this one.

    Circles get jagged in one side and round and nice in the other side. The different shaped hole edges are in the long axis (X).

    ANyone that can help me solve this? Using MACH3 and when milling wing cores with complex shape the result gets really nice. It is only when doing cutout files I get this. Maybe it is more information (points) when milling a wing foil???

    Thanks in advance, Kayaken

  2. #2
    Join Date
    Mar 2012
    Posts
    192

    Re: My homemade CNC router cant cut holes as it should? Anyone know what can be wrong

    I would usually look at backlash if you are not getting round holes. The jaggies not sure, maybe lots of backlash and some sticktion. How rigid is the gantry? How much can you bend it if you have a hand size tool in the spindle and you give it a good yank?

  3. #3
    Join Date
    Jun 2005
    Posts
    1723

    Re: My homemade CNC router cant cut holes as it should? Anyone know what can be wrong

    Check your ballscrew nuts. Looks like you have backlash on one of the axis

    Russ

  4. #4
    Join Date
    Aug 2003
    Posts
    72

    Re: My homemade CNC router cant cut holes as it should? Anyone know what can be wrong

    Must be the X axis then which uses belts :/ maybe that is the reason. have been looking rebuild that axis

  5. #5
    Join Date
    Apr 2003
    Posts
    540

    Re: My homemade CNC router cant cut holes as it should? Anyone know what can be wrong

    Yes you are either loosing steps due to a mechanical issue (loose coupler, pulley, belt, or binding due to misalignment/out of square etc) or because the motor speed or acceleration is to high/fast and the stepper is stalling. Check to ensure everything is good and tight. Something loose mechanically is normally the cause of such issues. If nothing is found, slow down your stepper speeds and acceleration and make some test cuts.

    A loose spindle/mount could also be the culprit so be sure and double check everything.

    Good luck.

  6. #6
    Join Date
    Aug 2003
    Posts
    72

    Re: My homemade CNC router cant cut holes as it should? Anyone know what can be wrong

    Hmmmm Unfortionatly I have to low gear ratio on my X axis (far less then I wanted) due to the restricted area under the bed. I would have liked to make this higer gear ratio (more steps on each mm travel) and maybe that would solve the issue.

  7. #7
    Join Date
    Apr 2003
    Posts
    540

    Re: My homemade CNC router cant cut holes as it should? Anyone know what can be wrong

    I know these types of issues can be frustrating. Out of round can also be Mach3 settings (IJ, CV Backlash etc) but the jagged edges look more like a mechanical issue. Incorrect drawing (how the cad is drawing segments, arcs and circles) can cause issues also... especially how your post processor handles the output. Specifically how it writes the gcode to cut arcs and radii.

  8. #8
    Join Date
    Jun 2012
    Posts
    108

    Re: My homemade CNC router cant cut holes as it should? Anyone know what can be wrong

    Looking at the picture of the circle cut in the wood if side to side is the X axis and top to bottom is Y axis I would say the X axis is the problem. I would guess the ball screw is the the X axis base on the picture of wood. The uprights on the CNC look like wood and only 3/4 of an inch. If you push on the top of an upright I bet it move a lot ( the wood bowing ) I don't think the steps in the cut are backlash as basklash would be seen when motor changes direction. I would grab the Z Axis and see if there is slop/movement in the X or Y directions.

  9. #9
    Join Date
    Mar 2012
    Posts
    192

    Re: My homemade CNC router cant cut holes as it should? Anyone know what can be wrong

    Quote Originally Posted by SteveWill View Post
    The uprights on the CNC look like wood and only 3/4 of an inch. If you push on the top of an upright I bet it move a lot ( the wood bowing ) I don't think the steps in the cut are backlash as basklash would be seen when motor changes direction. I would grab the Z Axis and see if there is slop/movement in the X or Y directions.
    I assumed they were aluminum, and even then I was a bit suspicious of the rigidity.

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