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  1. #1
    Join Date
    May 2019
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    Queensland, Australia
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    Default Using draw bore on half lap joint

    Hi all,

    I mainly (only?) see draw boring used to add additional mechanical reenforcement to mortise and tenon or bridle joints to help tighten and stiffen the joints. I'm working on a timber workbench and am wanting to do the same for the half lap joints I'm using to connect the rails to the legs, but I can't find too many examples online and so I'm wondering if draw boring a half lap would work at all. The reason I want to do it to ensure the joints (shoulder to face) are as tight as possible to eliminate any movement... I also don't have a clamp long enough (1.6 metres) to pull the joint tight for gluing.

    My concern with draw boring a half lap is that I imagine the pin will just want to rotate/lean-over to follow the offset of the two holes. This isn't a problem with mortise and tenon as the opposite wall of the mortise pulls the pin back square applying constant pressure to the hole in the tenon.

    Does anyone half any experience draw boring a half lap? Is it a waste of time to try? I'm thinking if I size the dowel large enough and go with a smaller offset, it should be enough just to pull the joint tight like a clamp for the glue-up. I don't imagine it'll improve the tightness of the joint over time like it would in a mortise and tenon.

    If it's deemed pointless, I guess I'll either source a longer clamp (get a longer pipe tapped for my bar clamps) or glue blocks to the middle of the rail and use that as a clamping surface.

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  3. #2
    Join Date
    Jun 2010
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    Bundaberg
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    Default

    I can't see it working myself although I'll stand corrected if someone has tried it. Drawbore pins need three points of contact; two loaded in one direction and the third loaded in the opposite direction and between the other two hence why bridle and MT joints are perfect for them.

    But; you can make cheap effective clamps as long as you like using 75 x 35mm construction timber and wedges.
    Nothing succeeds like a budgie without a beak.

  4. #3
    Join Date
    Apr 2006
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    Hobart
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    Default


  5. #4
    Join Date
    May 2019
    Location
    Queensland, Australia
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    Default

    Yeah well that's confirmed my suspicions, thanks for your replies. Oh well, glad I picked up on this now before wasting my time.

    I suppose if I didn't want to spend any money I could just use two of my pipe clamps together so they pull on eachother. I might be able to make that work, though might be handy to have a couple of longer threaded pipes for future projects as this won't be the last time I'll need a longer clamp. Hmm.

  6. #5
    Join Date
    Jun 2010
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    Bundaberg
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    Where in QLD are you? On the off chance you're in Bundy I have a pipe threader for 3/4" pipe
    Nothing succeeds like a budgie without a beak.

  7. #6
    Join Date
    May 2019
    Location
    Queensland, Australia
    Posts
    25

    Default

    Nah I'm up in Mareeba, Far North Queensland. I've looked at getting a 3/4" die, but the semi-decent ones are up over $100. I'll just go to the local metal engineering mob like I did last time.

  8. #7
    Join Date
    Sep 2022
    Location
    Brisbane
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    22

    Default

    Have you considered a tusked mortise and tenon?

  9. #8
    Join Date
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    Quote Originally Posted by Wardrop View Post
    ...Using draw bore on half lap joint ...
    A long-shot answer.

    We were in Japan before lockdown and visited a semi-antiques shop specialising sashimono joinery - some really spectacular craftsmanship. I absolutely loved it.

    The doors on one small cabinet seemed to have central rails secured with "draw bore lap joints". But it was sashimono, so what you think you see is not always what is actually there - those joints can be complex and deceptive. The joints looked something like this:

    Sashimo Draw Bore.jpg

    The proprietor spoke very limited English and my Japanese is far worse; nevertheless, we did attempt a conversation on how that joint worked. I think that he said that it was something like this:

    Sashimo Draw Bore 2.jpg

    It is quite possible that I got the translation wrong; at one stage I thought he was talking about sliding dovetails! But we were both probably using words and concepts that do not translate precisely, and we both had very limited language skills.

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