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IndustryArena Forum > MetalWorking Machines > CNC Swiss Screw Machines > Custom Thread Form for Mini Bone Screw (Citizen M20)
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  1. #1
    Join Date
    Sep 2013
    Posts
    4

    Custom Thread Form for Mini Bone Screw (Citizen M20)

    I'm making a small bone screw that specifies a custom buttress type thread form. I'm using a Citizen M20 machine. The major diameter of the screw at the threads is 1.4mm (.055"), and the threads run for about 11mm (.45"). I have tried single point threading without much success. I've tried threading in a single pass as well as breaking up the threading into three sections and blending the threading process. I've also supported the threading process from below with a custom support device attached to a position on the turrett.

    I'm wondering if anyone has experience threading a long small diameter screw? I'm looking into thread whirling as well as thread forming with a Fette Head. Any tips or tricks would be appreciated.

  2. #2
    Join Date
    Feb 2008
    Posts
    267

    Re: Custom Thread Form for Mini Bone Screw (Citizen M20)

    I think most shops that are "serious" about bone screws have gone to thread whirling.
    The methods you've attempted are all decent, especially for "casual" or infrequent bone screw jobs.
    Each has its own downside or pitfall but are not dependent on expensive/dedicated items.
    Good luck.
    Control the process, not the product!
    Machining is more science than art, master the science and the artistry will be evident.

  3. #3
    Join Date
    Sep 2011
    Posts
    261

    Re: Custom Thread Form for Mini Bone Screw (Citizen M20)

    Segmenting is about your only option without whirling. When you're making >5xD screws you pretty much have to segment or whirl.

    Also, since bone screws generally have a large width and high lead angle, single point threading does not work in every situation. like Pro said, any serious bone screw shop whirls.
    CNC Product Manager / Training Consultant

  4. #4
    Join Date
    Sep 2013
    Posts
    4

    Re: Custom Thread Form for Mini Bone Screw (Citizen M20)

    Thanks All! I monkeyd around with single point threading , segmented and non-segmented, and tried to support the threader with a custom support bracket from below. None of those methods worked for my project, but I did learn a lot about using the various modes available on the M20--threader from the tool post, support from the turret... I ultimately went to thread whirling, and my impression is that thread whirling is the only way to get this type of project done.

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