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  1. #41
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    Default Re: Hold me, I screwed up.

    I don't think your machine is losing position. Thermal expansion of everything, not just the tool holder and spindle nose, can easily add up to .003. High end machines have liquid cooled spindles and liquid cooled ball screws. They will also do a warm up cycle to get it up to temperature before starting. Even so if the shop is cold on Monday morning and heats up throughout the day as all the machines start working then tweeks have to be made.
    If you need that level of precision you will need to stop and reset the Z0 in the middle of the cycle. Just add an M1 before the finish pass and turn op stop on.



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    Default Re: Hold me, I screwed up.

    I usually let my spindle warm up. Start a 500rpm and work my way up to my working rpm's. Over 10 min or so.

    If you need that precise then i'd leave .01 or so, rezero your Z height, then finish.

    The other thing to think about is if your tool height is correct. If I need that close, I measure the tool, face a piece of material, flip it, then run the other side, pull it out measure the material, adjust tool height, cut again to check.

    Another thought..

    Maybe go for some thicker material, this way you dont have to get so close to the table. Flip it over and trim off the excess.



  3. #43
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    Default Re: Hold me, I screwed up.

    Quote Originally Posted by cobrakai View Post
    I guess if I have a total stickout from the spindle head of 3 inches (tool holder and tool), a rise in 50 degrees equals .0034". It could really be that simple huh?
    https://www.engineeringtoolbox.com/l...on-d_1379.html

    How do the pros deal with this? Run the machine for an hour, set the zero, then run the job?
    Most steels expand around 6e-6 in/in/degF. If you only consider the 3 inches of tool+holder+spindle nose then it will grow about .001 in 50degF change. The column, z-ball screw and spindle head need a much smaller temperature change to cause a greater change in position at the end of the tool.



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    Member Doug Darby's Avatar
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    Default Re: Hold me, I screwed up.

    This issue is exactly why I installed one of SMW fixture plates on my bed. works great but also is a last resort to keep from milling into the table. Simple to replace if you do.



  5. #45
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    Quote Originally Posted by IMT View Post
    Most steels expand around 6e-6 in/in/degF. If you only consider the 3 inches of tool+holder+spindle nose then it will grow about .001 in 50degF change. The column, z-ball screw and spindle head need a much smaller temperature change to cause a greater change in position at the end of the tool.
    I'm just getting more into cnc but think you have the answer " let your machine warm up " I have just recieved a Haas TM1P and while loading the collets a 19mm indexable endmill would not fit into the 3/4 collet untill the temperature normalized.



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    Default Re: Hold me, I screwed up.

    Quote Originally Posted by tom o View Post
    I'm just getting more into cnc but think you have the answer " let your machine warm up " I have just recieved a Haas TM1P and while loading the collets a 19mm indexable endmill would not fit into the 3/4 collet untill the temperature normalized.
    Was thinking Maritool offers cutters heat shrunk into holders. Kind of a cool idea and you would avoid this problem anyway. hehe



  7. #47
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    Default Re: Hold me, I screwed up.

    Quote Originally Posted by Doug Darby View Post
    This issue is exactly why I installed one of SMW fixture plates on my bed. works great but also is a last resort to keep from milling into the table. Simple to replace if you do.
    Those are really nice fixture plates for sure. I am too cheap to pay $900 for a fixture plate that I inevitably cut into. That's a big reason for my fixture plates, so that I can actually cut down to Z=0 and not have any burrs on sheet stock. I just plane the surface once it gets messed up enough and when it gets too thin I will make a new one.

    I've accepted that the damage to the table is now simply a constant reminder to consider all things that can affect precision work, like tool growth. It's easy to forget that one! It doesn't affect the function of my machine whatsoever and is outside of the workable area. Still a bummer, but not worth crying over (any more).



  8. #48
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    Default Re: Hold me, I screwed up.

    My Alum plate was only $340.. Black Friday weekend sale even cheaper.. But I understand..



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    Quote Originally Posted by Doug Darby View Post
    My Alum plate was only $340.. Black Friday weekend sale even cheaper.. But I understand..
    Where?!



  10. #50
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    Default Re: Hold me, I screwed up.

    NYCNC.com
    John Saunders.



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Hold me, I screwed up.

Hold me, I screwed up.