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Thread: Tool offset trouble

  1. #13
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    Default Re: Tool offset trouble

    Quote Originally Posted by rbickle View Post
    Interesting... Couple of questions though,

    So your offsets are calculated relative to machine coordinates z=0?

    The home position for my machine is not accurate. There are just some pointers on the X and Y axes. The Z just runs up to flush with the body. Not something that would be repeatable to 0.001".
    Couldn't use that position for an accurate reference point.

    I commonly have to move the knee on the milling machine, which changes the table height. In order to set up more tools later on, would I have to set the table to the same height as before?

    Currently my tool offsets are referenced to the shortest tool holder so that as long as you zero the part with the short tool holder, all other tool offsets are relative to that.

    Rick
    Yes offsets are calculated relative to machine coordinates Z=0. If you turn on tool length compensation and send the machine to Z zero in g-code (without a fixture offset) all the tools will move right back to the point you measured them. So your zero point for all tools is right at your tool setter.

    Then you use a fixture offset (g54. g55 etc) to shift all the tools from the place you measured them (tool setter), to your part. This is calculated automatically by kmotioncnc whenever you enter a value or zero out the DRO. For example if your tool setter is exactly 2.000 from table and you setup a part that happens to be 4.500 from the table... You touch all your tools off the tool setter, then move to the top of your part and zero out the DRO and Kmotion will calculate that you are now 2.500" higher and it will store this value for G54. Doing it this way also allows you to run several fixture offsets in one program which is handy sometimes.

    Ideally you should have home switches to reference the machine more accurately. Still might be slightly more helpful if you run 2-3 different jobs or setups without powering machine off. Maybe after a restart some tools might be good enough if not cutting critical features, like drilling through holes might be fine. Honestly, I didnt think about the Knee. I guess thats sort of a huge difference from a typical VMC in terms of setting work offsets. I supposed you could figure out some kind of procedure to set your knee back and the same place to set another tool. But that sounds like a pain to be honest, im not sure whats the best option if your moving the knee alot. That sort of changes everything. I guess you will have to give it some thought and find a system that works best for your machine. Good luck with it.



  2. #14
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    Default Re: Tool offset trouble

    Maybe later on I can make a more accurate home sensor for each axis. A metal tab with a fixed optical sensor would be pretty accurate. Might be a pain though to have the X and Y axes move several feet to home.
    If things go well, maybe I'll buy a bigger VMC and retrofit it too. This machine was just my first foray into CNC machining. A tool changer sure would be nice.

    Thanks for the info. on the offsets...



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    Default Re: Tool offset trouble

    Quote Originally Posted by rbickle View Post
    Maybe later on I can make a more accurate home sensor for each axis. A metal tab with a fixed optical sensor would be pretty accurate. Might be a pain though to have the X and Y axes move several feet to home.
    If things go well, maybe I'll buy a bigger VMC and retrofit it too. This machine was just my first foray into CNC machining. A tool changer sure would be nice.

    Thanks for the info. on the offsets...
    Well you could position everything closer then that before telling it to home. Another option might be to make your metal tab an inch or more long and you could travel toward home at a decent speed until the sensor detects an edge, then slow down and travel very slow and set the home position as you come off the other edge.

    Anytime, thanks.



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    Default Re: Tool offset trouble

    This is getting far too complex.

    If you don't have accurate homing, then touching of is perfectly acceptable provided you're consistent with your working method. I done it for a couple years with my old lathe.
    Power machine on, insert known tool into spindle, ensure offsets for that tool are active, touch of work piece, zero DROs.
    For any new tool, having established a reference, insert the new tool, touch it off the work piece, then update the tool offsets so it's now at zero.

    On that lathe I was still running Mach3, so it had a screen where setting tool offsets was reasonably easy. With KMCNC you have to write a suitable C program to calculate and store the offsets.
    Some methods say to have a dedicated 'master' tool that you never change, but once you have one known tool, all the tools become relative to that original tool. The only risk by not using the master tool to establish new offsets, is you can get accumulative offset errors, but with a bit common sense you soon learn what tool offsets need slight adjustments to keep everything consistent.

    Even if you had accurate homing, on a knee mill, unless you also home the knee, you still need to use the touch off method to establish height.



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    Default Re: Tool offset trouble

    Tom,

    I must be doing something wrong here. I inserted this code verbatim into a user button on KmotionCNC, and it just hangs.
    i tried running it on different threads, 4 and 6. The thread stays running and the button stays blue.

    Thanks,
    Rick


    Quote Originally Posted by TomKerekes View Post
    Hi rbickle,

    Here is code that you might assign to a User Button to Turn Off Tool Length Compensation.

    Code:
    #include "KMotionDef.h"
    
    #define TMP 10 // which spare persist to use to transfer data
    #include "KflopToKMotionCNCFunctions.c"
    
    main()
    {
        MDI("G49");  //Turn off Tool Length Compensation
    }
    Something to consider. The fixture selected and tool selected are shown in the dropdown itself. If you hover over the dropdown it does show the current offset. Although the Tool and Tool Offset corresponds to the loaded Tool and the Tool Table offset for that Tool rather than what Hxxx tool is enabled or selected.

    Regards




  6. #18
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    Default Re: Tool offset trouble

    Hi rbickle,

    Set the Action Type to "Execute Prog" without any wait. There can be a deadly embrace situation where the KMotionCNC is held up waiting for the C Program to finish but the C Program is waiting for KMotionCNC to respond. The latest Test Program 4.34j should no longer have that issue.

    Regards

    TK
    http://dynomotion.com


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    Default Re: Tool offset trouble

    That did the trick. Thanks Tom.



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