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IndustryArena Forum > MetalWorking > General MetalWork Discussion > Indexing issues on two-sided parts milled on 3-axis cnc machine
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  1. #1
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    Indexing issues on two-sided parts milled on 3-axis cnc machine

    How do you guys prevent indexing issues on parts that requiring turning half way through the job on 3-axis cnc machines?

    I've been advised that simply turning the part over manually is a better option than adding a low cost 4th axis (especially for milling metals). I just can't see how I would be able to position the stock and touch-off for the second side accurately.

    Do you guys have a trick for this?

  2. #2
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    Re: Indexing issues on two-sided parts milled on 3-axis cnc machine

    You can make a fixture with a couple of dowels sticking up on the center-line. This works if you're cutting your part out of a block of material, so that it remains suspended by tabs in a surrounding frame. The dowels slide into holes in the frame, and you release the clamps, remove the part, flip it over and re-clamp. Some CAM programs have routines for this as well.
    Andrew Werby
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  3. #3
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    Re: Indexing issues on two-sided parts milled on 3-axis cnc machine

    Quote Originally Posted by awerby View Post
    You can make a fixture with a couple of dowels sticking up on the center-line. This works if you're cutting your part out of a block of material, so that it remains suspended by tabs in a surrounding frame. The dowels slide into holes in the frame, and you release the clamps, remove the part, flip it over and re-clamp. Some CAM programs have routines for this as well.
    I can sort of see how using dowels could help me flip a part over while keeping it in the same place.

    It seems like I'd be better off with a cheap manual rotary table for indexing though (if I'm going to have the stock suspended between two fixtures anyway).

    I'll give it a try and see if I can manage to touch off in the right place after loading a 2nd gcode file for the other side. I usually gave to reset everything and re-zero in Linuxcnc whenever I load a new file.

    Have you tried the dowel method? If so, please can you post a pic of the fixtures you used to hold the part?

  4. #4
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    Re: Indexing issues on two-sided parts milled on 3-axis cnc machine

    Quote Originally Posted by Goemon View Post
    I can sort of see how using dowels could help me flip a part over while keeping it in the same place.

    It seems like I'd be better off with a cheap manual rotary table for indexing though (if I'm going to have the stock suspended between two fixtures anyway).

    I'll give it a try and see if I can manage to touch off in the right place after loading a 2nd gcode file for the other side. I usually gave to reset everything and re-zero in Linuxcnc whenever I load a new file.

    Have you tried the dowel method? If so, please can you post a pic of the fixtures you used to hold the part?
    You normally have a machined area where you can indicate your part, to reestablish your X Y Zero, that is how machinists do it, no amount of dowels is going to precisely relocate the part once you flip it
    Mactec54

  5. #5
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    Re: Indexing issues on two-sided parts milled on 3-axis cnc machine

    Quote Originally Posted by Goemon View Post
    I can sort of see how using dowels could help me flip a part over while keeping it in the same place.

    It seems like I'd be better off with a cheap manual rotary table for indexing though (if I'm going to have the stock suspended between two fixtures anyway).

    I'll give it a try and see if I can manage to touch off in the right place after loading a 2nd gcode file for the other side. I usually gave to reset everything and re-zero in Linuxcnc whenever I load a new file.

    Have you tried the dowel method? If so, please can you post a pic of the fixtures you used to hold the part?
    You don't rezero X and Y, that is the point.

    Plenty of videos around of the process
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  6. #6
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    Re: Indexing issues on two-sided parts milled on 3-axis cnc machine

    If the part has feature that is accessible from both sides like a hole or corner you can touch off from that feature after the flip. John Saunders of NYC CNC on YouTube has some good videos on work holding. Example here: https://www.youtube.com/watch?v=Liujqlj2cb0

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