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Thread: Simple Auto Retract Thread Cutting

  1. #11
    Supporting Member Canyonman44's Avatar
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    I would like to follow the motorcycle restoration! Ken

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    olderdan (Mar 8, 2021)

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    Supporting Member Toolmaker51's Avatar
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    I dislike under cuts also, radiused is first choice. Issue; as depth increases, hitting the 'center' gets trickier. So, when needed, I use a cut-off tool with edges radiused instead.
    Your manual kick-out is a creative answer. Can't imagine thinking of that solution, though did like pneumatic version operating the half nut lever here [hmt.net] awhile back.
    Some lathes kick feed out, can't think of any doing that for threading.
    Reasoned out why! Yours not actually kicking out, it's more a taper attachment. Kick-out would require retraction as well, unlike feeding to a shoulder.
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    Supporting Member tonyfoale's Avatar
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    Quote Originally Posted by Toolmaker51 View Post
    I dislike under cuts also, radiused is first choice.
    Maybe just a question of language but are not those the same. When I first mentioned undercutting it never occurred to me that anyone would consider one that was not radiused.

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    olderdan (Mar 8, 2021)

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    Supporting Member olderdan's Avatar
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    Quote Originally Posted by Canyonman44 View Post
    I would like to follow the motorcycle restoration! Ken
    I will post progress on the build but it will be a while as I have more work to do on my workshop. Tiling the floor, benches, wiring etc. Thanks for the interest.

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    Supporting Member olderdan's Avatar
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    Thanks for your input Toolmaker51, The main objective in making this was to enable single point threading at increased mandrel speed up to 400 RPM to get a better finish. It would also help in as you say hitting the centre point of a radiused undercut. The thread shown is a 26 TPI cycle thread only .0205 depth so a clean thread is important.

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    Supporting Member tonyfoale's Avatar
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    Quote Originally Posted by olderdan View Post
    The thread shown is a 26 TPI cycle thread only .0205 depth so a clean thread is important.
    It seems that all the old brit bikes used 26 tpi. I always knew it as Brass thread, only later did I learn that it was Cycle thread. There seems to be a difference in the angle though. 55 deg for brass and 60 deg for cycle. I still have a bunch of brass thread dies that I used in the 1960s, little realising that the studs that I was making were wrong. I had never heard of cycle thread at that time.

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    olderdan (Mar 8, 2021)

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    Supporting Member olderdan's Avatar
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    I also made that early assumption thinking that being british it would be the same as BSF and WHITWORTH form, metric is so much easier.

  11. #18
    Supporting Member Toolmaker51's Avatar
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    Quote Originally Posted by tonyfoale View Post
    Maybe just a question of language but are not those the same. When I first mentioned undercutting it never occurred to me that anyone would consider one that was not radiused.
    When I'm asked what drew me into operating machine tools or machinist [US phrase], or engineering [per the Continent]; our ability to convey an entire part verbally is what most impressed me, and that continues. Certainly beyond vocabulary of laymen or daily conversation, it IS widespread clearly among practitioners. Compare that how one particular phrase is argued incessantly......"shall not be infringed".

    For the three concerned; have we not mislabeled [or mixed continental meanings] that kind of design feature?

    For remaining audience, proper description hereabouts is "thread relief". Some are less than root depth, others just under pitch diameter. Intent preserves strength of a fastener calculated in square units, helps mating nut not jam on incomplete threads, reduces stray bits of material tear off and foul a mechanism. Despite that, we confer corner radii are part of a properly completed transition from thread to fastener body.
    An "undercut" defines a different feature; often to create 'square' corner, between a diameter with adjacent face. A proper turning tool is radiused at leading edge, that could interfere with a tight fitting mate, though a chamfer on the mate can accomplish same thing. In contrast, a relief is somewhat an O-ring groove, undercut more like a snap ring groove.

    Here is a side note. Does not a large diameter meeting a wide flange introduce a tool dilemma? That's easily conquered. With compound at 45, use carriage and cross slide to 'walk' a narrow bit into contact with both sides that 90 corner. Zero the compound dial, and back off. Spin part by hand and lay in Dykem or felt-tip marking. Proceed with cut, just a couple thousandths beyond corner insures a clear mating surface with least possible reduction of material.
    Reasons to use one or combinations of, enter into part design, materials, and workmanship; but I think most intertwined in tooling available/ processes of manufacture.



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    Last edited by Toolmaker51; Mar 8, 2021 at 10:39 AM. Reason: Clarity and definition; the Windex of muddlement
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    Toolmaker51
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