Scarfing, Splicing, join for Ply

Discussion in 'Fiberglass and Composite Boat Building' started by gary1, Nov 3, 2006.

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  1. PAR
    Joined: Nov 2003
    Posts: 19,126
    Likes: 498, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The circular saw attachments are only good for thin plywood. An 8:1 scarf (minimum recommended ratio) on 1/2" plywood is 4" long and not possible with a 7" circular saw blade.

    The scarf angle isn't particularly critical, the ratio is the key. Multiply the material thickness by the ratio (8) and this is the length of the tapered area on the piece. A 3/4" thick piece of wood, at an 8:1 scarf has a 6" long joint. 1/4" plywood is a 2" long joint.

    8:1 is the minimum taper and I often use higher, sometimes as high as 16:1.

    Get a laminate trimmer or router, setup with a flat bottom bit. Make a set of ramps, to border your work, that mimic the taper you desire, for the scarf you're about to make. Now screw the router or laminate trimmer to a piece of plywood that spans the work area, plus has enough room for the bit to travel from one side to the other. Clamp your stock inside the ramps and power plane most of the material out of the cut, them plow though what remains with a router.

    I have a few scarfing jigs. One is portable and can be clamped in place on the boat, the other is bench mounted and the ramp angle can be adjusted for different thicknesses of material. Frankly, after some practice, I've found I'm just as fast doing them by hand with a power plane to rough in and a hand plane and/or chisel to finish off, then with the jigs. The jigs provide machine precision, but the setup costs time. The hand method is fast, but lacks the machine accuracy. Practice on some scraps and you'll get the hang of it pretty quick with whatever method you choose. If you're using epoxy, the fits don't have to be perfict.
     
    PAR, Nov 11, 2006
    #16

  3. captainjsw
    Joined: Sep 2005
    Posts: 39
    Likes: 2, Points: 0, Legacy Rep: 24
    Location: Perth Western Australia

    captainjsw Junior Member

    Z join on DuFlex panel

    Sure I have seen the Z join and am using DuFlex panels now you are right its just an extension of the fibreglass on one face and a corresponding reduction of the fibreglass on the other side.

    Scarfing - I have done a lot and used a makita router - there is a special model that lets you adjust the angle of attack and hence the slope, its model N3720 - great tool I still have mine and will be using it again on the new boat. Thought I had a picture of it but I don't but I am sure there will be one out there on the web.

    Cheers John
    http://www.johnwatson.net.au
     
    captainjsw, Nov 30, 2007
    #17
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