Can a 7/8" UNF thread be tapped into 3/4" ID tube?

  1. rcx132

    rcx132 Philip

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    Location:
    London, UK
    I usually get this kind of work done at my friends workshop, but he's said his equipment is not up to it and it couldn't be done by hand.

    This is to make a panhard bar, clearance around the bar is tight so I wanted to tap straight into the tube rather than have to use pre-threaded weld in bungs which would increase the tube diameter.

    7/8" UNF requires a 20.4mm drilled hole to tap it out. The 3/4" ID tube has a 19.05mm hole, so I guess it would need boring out and then tapping.
     
  2. Milkybars

    Milkybars Member

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    Essex
    Whats the O/D of the tube ?
     
  3. hotponyshoes Member

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    Somerset. Uk
    I looked at doing this before for rose joints on a kit cars wishbones for weight saving.
    In my case the thick wall tube needed worked out to be heavier than fitting bushes in the ends.
    If space is at a premium maybe you could make an external bush for the ends rather than the normal internal type?

    To answer the question, yes you can providing the wall is thick enough to tap and you can run the tap straight enough.
    Ideally you will want seamless tube though or you might find you are cutting through the weld when opening it out.
    Another problem is finding tube that is round enough to start with plus tapping tube can be a pain as it can try and oval, either when you clamp it or as you try and get the tap going down it.
    If you can find a bit of 3/4" solid round bar you could stuff that down it and clamp it in a lathe chuck over the solid bit. If you had a set of 3 taps that would make things easier as well.

    Personally, if space is that tight I would look at going for a smaller tube and getting the strength back by using a stronger material.
    1/2" seamless chromoly or something? If you are only tight on space in one direction oval tube or a ladder bar.
     
  4. pedrobedro

    pedrobedro Man at Matalan

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    CX Derbyshire
    I welded nuts to the ends of my Panhard rod to fasten the rod ends to it. I used metric M12 because I could get them at a good price. You could thin them down after fitting to the end of the rod without needing any fancy equipment. I used 1" OD hydraulic tubing. A friend of mine made his from thinner tubing and it flexed a lot even though it was good stuff.
     
  5. graffian

    graffian Seer unto the end of his beard

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    It should hand thread fine I used to make bungs for -14 hoses by hand.
    the hard bit was grinding the square of the tap down to fit in a my little tap wrench.
     
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  6. rcx132

    rcx132 Philip

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    1,842
    Location:
    London, UK
    Oh right, so a few of you are saying I could do it by hand. The impression my friend gave is that I'd need to go to a workshop with bigger equipment!

    I'm still trying to figure out what size tube to use by looking at what others are using. But basically it would be something like 0.25" wall thickness so 1.25" tube for the panhard. The main links would be thicker tube.
     
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