Fillets and Pedantry

I have a very pedantic question: "Mask off the frames and bulkheads, leaving about 3/4" of wood exposed on either side of the joint."  Does this not produce a fillet that is overly large (and unsightly)?  Is this size critical to the strength of the fillet, and therefore the joint?   What about a total of 3/4" of exposed wood shared between the bulkhead and the hull?  Would this produce a fillet that is too small, and therefore not strong enough?   Thanks

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RE: Fillets and Pedantry

Oh good, pedantry. My favorite :-)

The fillet only has to be large enough to support the glass tape such that it will not fold, crease or pull away. The best way I've found to do this is to use a filleting tool with a rounded end. The exact radius of curvature depends on the thickness of the glass, but 5/8" is a good general purpose value that will work for up to 6 oz glass. That's about the same roundness as a nickel. My favorite tool is a plastic paint scraper with a rounded end. Others have successfully used beer bottles, plastic spoons, gloved fingers, etc. (click on images to emlarge)

I just put a glob of putty into one end of the seam, push the putty along the length of the seam with the rounded tool, scrape the hills from the edges with the flat tool and use that as the putty for the next length of seam. Depending on the joint angles, the seam can easily end up narrower than the space between the stitch holes, yet it's strong enough to survive paddling in a small craft advisory with 3 ft breaking waves.

As far as the masking tape goes, I never use it. I find it faster and easier to just use the scrapers. The masking tape method is good for first timers. It's also good for burying the wires. It's also quite fast when used in conjunction with the pastry bag method of applying the putty. It's a good production schedule technique for situations where the seams need to be done very quickly and reliably (by possibly inexperienced builders). But when time is not money, when I have the leisure to pull the stitches first, I like the thin fillets better.



RE: Fillets and Pedantry

Thanks, Laszlo.  I tend to agree about the masking tape.  I was satisfied with my first attempt at filleting, but after removing the masking tape I  stiil needed to smooth out the spot where the epoxy met the tape.  I've removed all the stitches in the hull and will heed your advice when it comes to glassing the seams before glassing.


RE: Fillets and Pedantry

I should have written "filletting" the seams before glassing in my previous message.  I have since read in my epoxy manual that a filletting tool of 30mm (approx. 1.25") is recommended for 6mm ply in order to achieve the maximum strength; this applies only to a near perpendicular butt joint where the bulkheads meet the hull, and does not apply to filletting the seams prior to glassing. 

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