Scarf alingments?

Discussion in 'Wooden Boat Building and Restoration' started by BHOFM, Aug 20, 2008.

  1. Oyster
    Joined: Feb 2006
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    Oyster Senior Member

    This is an interesting read. Do you have a full sized shot of your boat? Thanks
     
  2. dsuursoo
    Joined: Aug 2008
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    dsuursoo Senior Member

    something i've learned from building bows for archery:

    glue on a roughed surface has no more bonding strength than glue on a smooth surface. there's no increase in surface area when you rough it up first, as far as the adhesive is concerned.

    far better is to create a sawtoothed tool that makes a set of grooves in each side of the joint, so they fit perfectly together. you can more than double your surface area, and have a significantly stronger peice of wood.

    just my experience.
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Actually tests have clearly shown that gluing, regardless of the type used, is much better (stronger glue line), if the parts being joined have shaved faces. The only cutting tools that will do this are the hand planes and the scraper.

    It's actually quite simple if you magnify the ends you're gluing and have a look. With rotary cut tools, the tubules (wooden cellular structure) are torn apart, ragged and smashed, from the violence of the usually carbide tipped blade, swinging through it at high speed. With reciprocating tools the same is true.

    With a shearing tool, used slowly, like a hand plane or scraper (assuming a sharp blade), the tubules are cut cleanly, leaving their exposed ends to receive what ever glue to apply. The smashed and torn tubules don't accept much if any glue, therefore no penetration into the wood's cellular structure.

    Epoxy on the other hand requires a rough surface to work. It must have a gap, a place where the epoxy can live. If the parts fit precisely, the glue can be easily oozed out when pressure is applied, destroying the effectiveness of the joint. I design all epoxy joints with a 1/16" gap. This insures the goo can't squeeze out. I just hung a set of side deck beams, each epoxied to the sheer clamp and coming carlin. They were cut 1/8" short and placed in position with 1/16" spacers (popsicle sticks), until the epoxy kicked off. The spacers where then sanded flush and all looks perfect for paint.
     
  4. dsuursoo
    Joined: Aug 2008
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    dsuursoo Senior Member

    that's actually what i'm talking about. it's tough to describe in print, but you draw the tool down the face to be glued, much like a comb. the set of grooves you make, when joined to a matching glued surface, increases the surface area total. increasing surface area=more glued surface=greater bonding strength. the same applies to epoxy, it just takes a different tool. something that makes grooves shaped more like gear teeth would do nicely(leaves gaps, with some points of contact.

    it's actually a really neat trick, and easy to make. give it a swing.
     
  5. mongo75
    Joined: Aug 2007
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    mongo75 Senior Member

    Hey Bhfom- Why Are You Ending Every Sentence With A !!!!!!!!!!!!!!!!

    Lol
     
  6. BHOFM
    Joined: Jun 2008
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    BHOFM Senior Member

    It is a bad habit I picked up from some one that ends all
    theirs with "!!". Besides, some end with "?".

    :p :p :p :p :p :p
     
  7. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    Habit maybe but not so bad..........................
    :rolleyes:
     

  8. mongo75
    Joined: Aug 2007
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    Location: Orange County California

    mongo75 Senior Member

    I've got worse habits myself hehe
     
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