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    Member popspipes's Avatar
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    Default Backlash

    I am having a problem holding tolerance, its about .0015 off from perfect across the sides when cutting a hex boss.

    I thought the Backlash setting would cure this but it didnt??
    It really helped with probing when entered into the Pathpilot appropriate.ini file, I am wondering if it has any effect on the actual cutting of a part in other than the x or y directions its off in a varying degree in the angle directions??

    I was repurposing allen wrenches that had been in the drawer for over 40 years, and I noticed that the dimensions were off slightly, doesnt make much difference, just want to know why??

    I cut a .750 hex in 6061 and it was off by the same ammount in the diagonal directions, more of a curiosity thing as I am not making precision parts............

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    mike sr


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    Default Re: Backlash

    A deviation of 0.0015" can easily be the result of less than ideal toolpaths and finishing strategies. Aside from which, without "tweaking", getting better than 0.002" precision is as much a matter of luck as anything else. Thermal expansion can account for such an error, as can machine flex, tool flex, backlash, friction/stiction, under/over-sized tools, and a host of other issues. Bottom line - what you're seeing is about what you should expect, unless you're willing to iteratively "dial in" each part.

    Regards,
    Ray L.



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    Default Re: Backlash

    On a simple part like the hex I could just redraw the part and move the appropriate sides in or out the amount that they are off..........
    Kind of sounds like busy work though??

    I thought the backlash settings would solve this but that wasnt the case.

    mike sr


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    Default Re: Backlash

    Changing backlash settings will only help if the problem is backlash. Otherwise, you're adding a different error.

    Regards,
    Ray L.



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    Community Moderator Jim Dawson's Avatar
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    Default Re: Backlash

    Many (most?) endmills are not exactly on size, solid carbides especially tend to run a bit small. I have seen some that were 0.005 small. You have to measure the endmill that you will be using and plug that number into the CAM program or compensate with the cutter comp setting. If your part measures the same across all flats, then it's probably not backlash.



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    Default Re: Backlash

    The cutter size I am aware of, I change that in the CAM to the measured size.
    The measurements I am refering too are across different pairs of flats Y measures .623, XY diagonal is .6245, the other diagonal is .6235 (dont know the proper term for this).

    mike sr


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    Default

    You are getting some very good results, Mike, considering that Tormach itself states that their machines are capable of .003


    QUOTE=popspipes;2088890]The cutter size I am aware of, I change that in the CAM to the measured size.
    The measurements I am refering too are across different pairs of flats Y measures .623, XY diagonal is .6245, the other diagonal is .6235 (dont know the proper term for this).[/QUOTE]



  8. #8
    Community Moderator Jim Dawson's Avatar
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    Default Re: Backlash

    Given the new information you provide, I will say that it may be backlash. Try interpolating a 2 inch circle and take several measurements at different points. See if you get results consistent with your results above.



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    Default Re: Backlash

    Quote Originally Posted by Jim Dawson View Post
    Given the new information you provide, I will say that it may be backlash. Try interpolating a 2 inch circle and take several measurements at different points. See if you get results consistent with your results above.
    Jim, the holes are off by about the same amount.

    I have the X and Y ways a bit too tight, I did put in the backlash for each axis, works fine for probling, not so much for cutting parts.

    It really doesnt make that much on the parts I make, just trying to figure out why.

    We like to think of steel parts and machines as being ridgid when actually they are not, steel is a bit of a spring when we get to splitting hairs...........

    mike sr


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    Default

    Have you checked your spindle? Mine is out quite a bit. There is a good video on YouTube on how to lap it using cold blue/diamond hone.
    Spindle error won't account for the circle being out of true, though.


    Quote Originally Posted by popspipes View Post
    Jim, the holes are off by about the same amount.

    I have the X and Y ways a bit too tight, I did put in the backlash for each axis, works fine for probling, not so much for cutting parts.

    It really doesnt make that much on the parts I make, just trying to figure out why.

    We like to think of steel parts and machines as being ridgid when actually they are not, steel is a bit of a spring when we get to splitting hairs...........




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