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Thread: boring holes in gaff / boom jaws

  1. #36
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    Default Re: boring holes in gaff / boom jaws

    Do a test in scrap for bore size. A full 1/16th undersize might be too tight and cause a split. I'd want a driving fit, but not with your biggest hammer. If you are gluing the cheeks, you already have plenty of shear strength in my opinion.

  2. #37
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by J.Madison View Post
    Do a test in scrap for bore size. A full 1/16th undersize might be too tight and cause a split. I'd want a driving fit, but not with your biggest hammer. If you are gluing the cheeks, you already have plenty of shear strength in my opinion.
    That is why I was cautious about the jaws of harder wood. Should be OK through the soft of the spar. However if gluing, it is less of a worry, but then why bolts?
    It really is quite difficult to build an ugly wooden boat.

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  3. #38
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    Default Re: boring holes in gaff / boom jaws

    Hey, This is very interesting to me.

    So if this joint is all in shear how does Wizbang's lashed gaff jaws handle that shear force ? I would think something seized could only apply a tension.

    Do you guys know off hand how well ships augers drill to their size ? Are the sized based on the bolt diameter vs the hole ?

    Cheers,
    Mark

  4. #39
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Mark0 View Post
    Hey, This is very interesting to me.

    So if this joint is all in shear how does Wizbang's lashed gaff jaws handle that shear force ? I would think something seized could only apply a tension.

    Do you guys know off hand how well ships augers drill to their size ? Are the sized based on the bolt diameter vs the hole ?

    Cheers,
    Mark

    Bits of the same size all bore slightly different diameter holes. Over the years I have aquired a fair selection of bits for boring long holes, among them ship augers, electricians long twist bits and regular augers. When faced with a job where sizing is important there's a fair amount of trial and error takes place trying out different bits to find the right diameter for the bolt or drift at hand. It's not unusual to have a bit that will bore a hole too tight for a long drift in hard wood but be fine for the same drift in softwood. The point is, you have to experiment. In a situation like yours I would try for a tight, driving fit to take advantage of the sheer strength of the bolt

    Drilling holes...you'd think it would be simple, but it don't hafta be.

    Jim
    Last edited by Jim Ledger; 08-12-2019 at 07:17 PM.

  5. #40
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    Default Re: boring holes in gaff / boom jaws

    I believe that banging bolts through tight holes like that, is a thing from the past, best used for underwater members.
    Not for a spar.

  6. #41
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    Default Re: boring holes in gaff / boom jaws

    Once it's epoxied in place the bolts are almost redundant. I'd just use countersunk lags with washers. If you stagger them you can run them almost all of the way thru. You can even dump some epoxy into the bored holes and spread it around with a small dowel first, just because.

  7. #42
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    Default Re: boring holes in gaff / boom jaws

    Some people just like "banging bolts through tight holes".

  8. #43
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    Default Re: boring holes in gaff / boom jaws

    Take your pick.

    While advocating trial and error to find the bit that gives a reasonably snug fit I would caution against anything that might split these relatively small parts. It's not as if you were driving into a keel timber here. Three bolts in a row near the end of a Fir spar could easily split the spar, and the same goes for the jaws.

    As far as gluing the jaws goes without any mechanical fastening my concern would be the relative weakness of the Fir itself. While the glue joint would most probably hold, the underlying wood of the spar might be prone to splitting off, most likely from the front and working back. Through bolts address this problem and allow the glued joint to remain intact under heavy stress.

    Jim

  9. #44
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    Default Re: boring holes in gaff / boom jaws

    Hi,

    There has been lots of mention about gluing the jaws to the spars, but I'm thinking that we will remain traditional in this sense and just have them mechanically fastened with some bedding compound. There is lots of material for bolts, the gaff jaws are 3 inches thick, boom jaws are 4 inches..... Sorry wizbang, but they are white oak.... it's the local hardwood around here

    Thanks for all the replies, I really like these technical discussions on the forum.

    Cheers,
    Mark

  10. #45
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    Default Re: boring holes in gaff / boom jaws

    Ask 10 people, get 11 different answers. Half of them are probably right! Good luck.

  11. #46
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    Default Re: boring holes in gaff / boom jaws

    Glueing them with epoxy, especially if you include a layer of 10 oz. cloth in the joint, will not only exclude moisture it will go a long way towards preventing splitting.

  12. #47
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by J.Madison View Post
    Ask 10 people, get 11 different answers. Half of them are probably right! Good luck.
    Only the half I agree with are right

  13. #48
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    Default Re: boring holes in gaff / boom jaws

    The thing about gluing them is that it makes it much more difficult for repair / replacement
    Cheers,
    Mark

  14. #49
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    Default Re: boring holes in gaff / boom jaws

    Just re glue/glass the bit which broke off.

  15. #50
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Mark0 View Post
    The thing about gluing them is that it makes it much more difficult for repair / replacement
    Cheers,
    Mark
    Not really Mark. Just whack most of it off with a hatchet or whatever then plane the rest.

    If you use lags in epoxy once they are exposed heat them with a torch and they'll come right out.

    I'll shut up now.

  16. #51
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Mark0 View Post
    The thing about gluing them is that it makes it much more difficult for repair / replacement
    Cheers,
    Mark
    Band saw...
    Hand saw...
    Epoxy just gives right up

  17. #52
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    Default Re: boring holes in gaff / boom jaws

    Hi,
    Just out of interest, on page 43 of Bud's How to build a wooden boat he has the following to say about sizing holes for drifts:
    "Once we tried boring them a sixteenth scant, according to the book - in hard, dry oak mind you - and had them fold like spaghetti before they were halfway home"

    I haven't found any other references for bolt holes in wood specifically.

    Cheers,
    Mark

  18. #53
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    Default Re: boring holes in gaff / boom jaws

    There being so many variables, type of wood, drift material, drift length, and so on it would be difficult to make a chart. A sixteenth under seems a lot unless you're drifting into a yellow pine keel timber. Tests on scrap is your best bet.

    Jim

  19. #54
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Jim Ledger View Post
    There being so many variables, type of wood, drift material, drift length, and so on it would be difficult to make a chart. A sixteenth under seems a lot unless you're drifting into a yellow pine keel timber. Tests on scrap is your best bet.

    Jim
    The 1/16ths under was common enough practice in boat yards building fishing smacks and larger, driving through oak or wet elm.
    I have seen a technique in the museum of shipbuilding in Brest castle where for long bolts through the stern deadwoods the copper bolt was reduced in diameter over half of its length, and the hole bored with two corresponding diameters. That way the copper bolt was being driven through air for half of its length.
    It really is quite difficult to build an ugly wooden boat.

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  20. #55
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    Default Re: boring holes in gaff / boom jaws

    Wet wood/dry wood, yet another variable.

  21. #56
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    Default Re: boring holes in gaff / boom jaws

    Quote Originally Posted by Mark0 View Post
    The thing about gluing them is that it makes it much more difficult for repair / replacement
    Cheers,
    Mark
    Too much reading . This is usually true of devil sperm 5200, but not epoxy.

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