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Scarf Joint Questions

Posted by DenverGaper 
Scarf Joint Questions
January 29, 2017 11:07PM
I'd like for first of thank everyone on this forum. It has been extremely helpful in reading through to solve a lot of questions that I have been having during my first boat build.

After contemplating all the different ways to make a scarf joint I decided to try it by hand. The first practice went really well on 3/8" ply with a 8:1 ratio cut, rather 3". I then decided it was time to give it my initial go. I went for a 12:1 ratio on 1/4" plywood.. Also 3". This go around did not turn out nearly as clean. Which brings me to my question.

Should I scarp this joint and give it another go? Or do you think I can salvage it and continue to clean it up regardless of the tear out?

Below is a link to the blog of the boat build. Hopefully it will provide the pro's some humor to rookie mistakes, and guide other rookies by showing them how it has been going for a complete amateur builder.

Re: Scarf Joint Questions
January 30, 2017 02:07PM
It's hard to tell from your photos how much tear out there is. Partly because I have CSS (similar to CRS). But I have a hunch it will be just fine.

From your blogs it looks like you are using hand planes. If you sharpen the blade so it can shave the hair off your forearm, and if you then stroke it over the joint at a 45 degree angle it should make a baby's bottom smooth joint. If you touched that one up a bit more, just enough to make it smooth, it might make the boat 1/16th inch shorter.

3" inches shorter doesn't really matter. My guess is the joint could be used now, but it's hard to tell from the photos. Touching it up a bit won't change much so perhaps that's the best way to go.

When you glue it together do it over top of visqueen. Wet out both sides of the joint with warm thin resin. Then slobber on an even coat of resin thickened to a yogurt consistency. Position the panels in a dead straight line along one edge. Put visqueen on top. Put plywood on top of that. Screw down through the whole thing from top to bottom many times. The holes left by the screws will disappear when the panels get glassed.
Re: Scarf Joint Questions
January 30, 2017 09:57PM
A little tear out shouldn't hurt the joint. If the joint is too tight you actually can get an epoxy starved joint. A bit of roughing of the surface actually will make it stronger.
Re: Scarf Joint Questions
February 03, 2017 06:30PM
Thanks for the advice. I definitely need to sharpen the hand plane blades. Working on that mission now. Can't wait to see how big of a difference it makes.
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