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  1. #1
    Join Date
    Dec 2003
    Posts
    189

    CNC metal C frame build

    After posting a query regarding the possibility of building a mill from structural steel tubing and then filling the tubes with concrete I've taken the plunge.

    Here the parts are mocked up in my shop with clamps to give me an idea of how the finished machine might look.
    clamps to give me an idea of how the finished machine might look.
    Attached Thumbnails Attached Thumbnails IMG_6520.JPG  

  2. #2
    Join Date
    Dec 2003
    Posts
    189
    I got everything lined up and welded in place and readied the kiln to stress relieve the frame before grinding/fly cutting the mating surfaces true.

    My wife built a pottery kiln some years back and I was in luck it fit in no problem.

    Next I brought the base and upright to temperature or 1150 degrees for 5 hours.

    When done, I shut off the gas and waited for it to cool.

    It's done when a toothpick comes out clean right?
    Attached Thumbnails Attached Thumbnails IMG_6523.JPG  

  3. #3
    Join Date
    Dec 2003
    Posts
    189

    Talking

    Here's a CAD file of the design.
    Attached Thumbnails Attached Thumbnails tubemill_1.jpg  

  4. #4
    Join Date
    May 2005
    Posts
    405
    Nice work. I'm a bit ignorant on the use of concrete in steel. Is reducing the strees a requirement for the concrete or for the grinding?
    Paul

  5. #5
    Join Date
    Oct 2006
    Posts
    64
    Paulc: no expert, but i think you want to stress relieve the steel (or alot of materials) before you final machine the components true to get all of the movement out of the material. IF not stress relieved, if you machine something thinking ur gonna get acccurate parts, the material will move, or spring in some unknown direction, and ur parts won't be what u think ur getting.

    1 So stress relieve

    2 Machining

    3 Sometimes for BIG parts, another round of stress relief

    4 Final maching

    5 inspection

  6. #6
    Join Date
    Jul 2005
    Posts
    12177
    When you do your machining I suggest you take everything down to within 0.020" of the final dimensions and check to see if things have distorted. You have welded together very different thicknesses and your first stress relieving may not have released all the stresses between these sections.

  7. #7
    Join Date
    Dec 2003
    Posts
    189
    It looks as if I will have to have the mating surfaces to the bearing rails ground but will have to have the end of the base fly cut as it won't fit on any grinder in town. This shouldn't be a problem as it would be easy to shim if necessary the uprights to the base.

    L

  8. #8
    Join Date
    Mar 2005
    Posts
    76
    Good idea.
    Where is a good source for the ball screws etc.
    Why not just use thicker cross section steel instead of the concrete?
    Is there any info on here about using concrete?

  9. #9
    Join Date
    Dec 2003
    Posts
    189
    The mill is reall coming along now. It's back from the ginding shop and I've had several days to work on it.
    Attached Thumbnails Attached Thumbnails IMG_6526.JPG  

  10. #10
    Join Date
    Dec 2003
    Posts
    189
    OK, gang, I'm really getting into it. Here's a shot of the z axis stand-off blocks coming together. Notice the sweet finish the facemill leaves on the aluminum!

    Nice!
    Attached Thumbnails Attached Thumbnails IMG_6532.JPG  

  11. #11
    Join Date
    Dec 2003
    Posts
    189
    tolerances are looking really good, so far .00005 or better.
    Attached Thumbnails Attached Thumbnails IMG_6534.JPG  

  12. #12
    Join Date
    Dec 2003
    Posts
    189
    Quote Originally Posted by Bill Johns View Post
    Good idea.
    Where is a good source for the ball screws etc.
    Why not just use thicker cross section steel instead of the concrete?
    Is there any info on here about using concrete?

    The concrete will dampen the natural resonance of the steel tubing.

    When unfilled the tubes ring like bells.

  13. #13
    Join Date
    Oct 2006
    Posts
    64
    nice work so far, keep us posted!

  14. #14
    Join Date
    Jul 2005
    Posts
    12177
    Quote Originally Posted by Bill Johns View Post
    Good idea.
    Where is a good source for the ball screws etc.
    Why not just use thicker cross section steel instead of the concrete?
    Is there any info on here about using concrete?
    This thread is about using concrete and there is a link to a Ph.D. thesis about machine building that has detailed information.

    http://www.cnczone.com/forums/showth...hlight=bamberg

  15. #15
    Join Date
    Aug 2003
    Posts
    812
    How did you figure half a tenth on a one thou indicator?

  16. #16
    Join Date
    Dec 2003
    Posts
    189
    Mill frame has been striped down, painted and ready for final assembly.

    Oh oh!, I broke a tap in the last of the sixteen 1/4- 20 holes that hold down the large THK rails for the Y axis. It was late in the day and the tap was showing it's age.

    I cursed the tap but quickly got to work. I spoke with a fellow machinist last week and he told me about a technique for removing busted taps and bolts. I didn't know how it would work but gave it a try.

    I switched on the power to my TIG welder and dialed the power setting down to a mear 20 amps. slowly I began to heat what little of the tap was sticking up above the rail pad. I began to build up the tap with fill rod until I had a 1/4 inch of so protruding from the hole being ever so careful not to weld the remainder of the tap to the machine itself.

    I slipped a 1/4-20 un-plated nut over the protrusion and welded it to it.

    A minute or so later I gave it a shot of WD-40 and applied a 7/16 wrench to the nut and slowly rocked the nut back and forth. To my joy and amazement the tap simply backed out of the hole and was ready to go after two quick passes with a file to clean up around the freshly taped hole.

    This is a nice way to finish a day's work!
    Attached Thumbnails Attached Thumbnails IMG_6539.JPG   IMG_6540.JPG  

  17. #17
    Join Date
    Mar 2004
    Posts
    1661
    This machine develops really nicely, looks good to me!

  18. #18
    Join Date
    Mar 2004
    Posts
    1306
    Nice work. Thanks for posting lots of pictures.

    Are you really planning to use the round rods as linear guides for the Z axis? The flex in those will easily exceed any benefit gained by damping the bed.
    Regards,
    Mark

  19. #19
    Join Date
    Dec 2003
    Posts
    189
    No round Thompson slide table was just to get an idea for positioning. Z axis is THK 20 series linear slides and 5/8's ballscrew.


    Quote Originally Posted by RotarySMP View Post
    Nice work. Thanks for posting lots of pictures.

    Are you really planning to use the round rods as linear guides for the Z axis? The flex in those will easily exceed any benefit gained by damping the bed.

  20. #20
    Join Date
    Dec 2003
    Posts
    189
    Basic machine is nearly complete. Will post some more pics soon.

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