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  1. #1
    Join Date
    Nov 2013
    Posts
    6

    Accuracy issues

    I've had my pro 4896 running for a few months now and have been very happy with it so far. I've had problems here and there but was able to fix them fairly easily. I have a problem I just noticed and could use some help. I was cutting 8 identical rectangles and they didn't come out identical. They varied in width by 1/8". They should have all been 6-1/2" and some were 6-7/16 and some were 6-9/16. I need to fix this.

    I have the plug n play nema 34 from cnc router parts.
    Using a hitachi router with precise bits collet

    Any help would be great. Thanks

  2. #2
    Join Date
    Mar 2011
    Posts
    584

    Re: Accuracy issues

    Are all the squares actually squares? Meaning are both legs the same size?

    Did you actually check the move distance of each axis? Its pretty easy to do in mach 3

    Did you put loctite on the jam screw for everything?

    Were these cuts a single full depth profile cut or multi, if multi were the sides stair stepped.

    How fast were you cutting them feed rate and DOC?

  3. #3
    Join Date
    Mar 2003
    Posts
    35538

    Re: Accuracy issues

    When you finished, did you check to see if the machine had lost position?
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  4. #4
    Join Date
    Feb 2005
    Posts
    829

    Re: Accuracy issues

    I second the loctite on the set screws. This appears to be a common oversight on the CRP machines, without locktite on the stepper belt pulley they come loose and you lose position quite easily.

  5. #5
    Join Date
    Apr 2012
    Posts
    11

    Re: Accuracy issues

    Try one thing at a time.
    Where did I put those steps - YouTube

  6. #6
    Join Date
    Feb 2005
    Posts
    829

    Re: Accuracy issues

    graffix, exactly. Only reason I backed up the suggestion on the pulleys because its a common issue with the CRP machines.

  7. #7
    Join Date
    Nov 2013
    Posts
    6

    Re: Accuracy issues

    Thanks for the replies...

    Are all the squares actually squares? Meaning are both legs the same size?

    Yes

    Did you actually check the move distance of each axis? Its pretty easy to do in mach 3

    No, can you tell me how to do this? Or show me a place that explains it? Thanks

    Did you put loctite on the jam screw for everything?

    Yes I used loctite on almost everything

    Were these cuts a single full depth profile cut or multi, if multi were the sides stair stepped.

    They were a single full depth cut in 1/2" plywood with an amana 1/4" compression bit

    How fast were you cutting them feed rate and DOC?

    35 imp conventional


    Thanks again, I'm going to do some trouble shooting tonight or tomorrow

  8. #8
    Join Date
    Mar 2003
    Posts
    35538

    Re: Accuracy issues

    Quote Originally Posted by ger21 View Post
    When you finished, did you check to see if the machine had lost position?
    ..
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  9. #9
    Join Date
    Nov 2013
    Posts
    6

    Re: Accuracy issues

    No, not sure how to do that.

  10. #10
    Join Date
    Apr 2014
    Posts
    0

    Re: Accuracy issues

    When you start your job, you set your X and Y (and Z) to a certain point and zero them. This point may be the center of your material, or a corner, etc. This is your job zero.

    Once you have run through your cut file, send the machine back to the job zero by typing G0 X0 Y0 in the MDI (if it didn't go there at the end of the file on its own). If the machine doesn't return to the exact spot you set at the beginning, you have lost steps.

  11. #11
    Join Date
    Mar 2011
    Posts
    584

    Re: Accuracy issues

    Quote Originally Posted by LongIslandWood View Post
    Thanks for the replies...

    Are all the squares actually squares? Meaning are both legs the same size?

    Yes

    Did you actually check the move distance of each axis? Its pretty easy to do in mach 3

    No, can you tell me how to do this? Or show me a place that explains it? Thanks

    Did you put loctite on the jam screw for everything?

    Yes I used loctite on almost everything

    Were these cuts a single full depth profile cut or multi, if multi were the sides stair stepped.

    They were a single full depth cut in 1/2" plywood with an amana 1/4" compression bit

    How fast were you cutting them feed rate and DOC?

    35 imp conventional


    Thanks again, I'm going to do some trouble shooting tonight or tomorrow
    This video explains how to calibrate the steps per inch.

  12. #12
    Join Date
    Feb 2004
    Posts
    1086

    Re: Accuracy issues

    LongIslandWood,

    Looks like you are getting some good advice here, but feel free to contact us directly tomorrow if you'd like some assistance. I doubt your issue is a steps/inch setting problem -- if it was, all of your rectangles would likely be off the same way. My guess is that something is loose mechanically. We'd be happy to walk through some things with you to try and sort out the issue more quickly.

    Best regards,

    Ahren
    CNCRouterParts

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