plywood scarf jig

Found this online and was wondering if anyone has used a jig like this. Looks like a quick and easy way to go, especially if you are building boats on a regular basis.

http://www.oneoceankayaks.com/stitchglue/plyshophtm/scarfjig2.htm

I am starting a boat and just finished my first plywood scarf joint. Did it the traditional way as described in Roger's book. Started with a belt sander, then finished up with a 5" orbital. First attempt I got a little carried away and the thin edge started to feather. So redid the scarfing process and think I left a little too much meat on the thin edge. The joint came out OK, but there is about a 1/4 inch seam line down the plywood panel. I used saw dust to thicken the epoxy which is what left the brown seam line. Looking at my Tatman kit boat, their scarf joint is really clean. So.....definitely need some work on my technique. I am using fir marine plywood and am planning to paint the boat anyway, so the highly visible joint is not that big of deal. But at some point would like to build a boat using meranti or sapele with a spar varnish finish which will require nice tight scarfs. A jig like in the above link looks to be a good way to go.

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Permalink Reply by Stephen Markley on July 8, 2012 at 8:33am

Great Idea... thanks for posting that!

Permalink Reply by Jack Rose on July 10, 2012 at 10:04pm

Kurt, I was at the same point back in the winter and saw that same link.  The problem that I ran into was that many folks in this forum recommend a 1:12 scarf ratio.  So, on 1/2" plywood, you'd need a circular saw that can make a 6" deep cut.  But a typical 8" blade struggles with a 3 1/2" cut.

Not to be deterred, I went ahead and set up the jig, and rented a 16" saw that's used for timber-framing.  It would have worked great, and been worth every bit of the $35 it cost me, had the blade been anywhere near sharp. 

Unfortunately, it made a mess, so I went with the belt sander idea.  It took a good bit longer, but it worked just fine.


Jack

Permalink Reply by Greg Jensen on July 11, 2012 at 9:07am

Kurt - I too started a boat this winter and saw the same jig diagram. Because I used a 12:1 scarph and couldn't find a saw big enough to make that cut, I came up with an easier jig to use with a router. The nice thing about the router is you can make your scarph any size you want with very limited changes. I know posted some diagrams and pics of my jig on this site.  Take a look in the search engine  "scarph" dated 3/26/12. The scarph shown in that pic was the 1st I had ever done and with a little sanding it worked out great. Since then I have done 4 more scarphs from 4' to 8' widths, and with a little practice the router worked fantastic.

Good luck and have fun.

Permalink Reply by Jack Rose on July 11, 2012 at 10:51am

Greg, great idea.

I wish I'd seen your post before I spent several hours with a belt sander. Your jig idea removes my reticence to go through that again.

Here's the link: http://westcoastwoodenboats.ning.com/forum/topics/greg-s-drift-boat...

Jack

Permalink Reply by Vance Wonser on July 12, 2012 at 9:51am

Since I have so little experience I'm missing how the router jig works on the scarf joints.  Anyone with a video????

Permalink Reply by Rick Newman on July 12, 2012 at 3:47pm

Vance, try a quick search on Google there are several videos for "cutting a scarf with a router" they will give you the idea.

Rick Newman

Permalink Reply by Phillip Westendorf on July 12, 2012 at 7:40pm

Kurt,

Take a look at Guy's Wooden Drift Boat Project, Page 10, March 21, 2012, on this forum.  There are some nice pictures of the jig Guy used to scarf his Sheer Rails, Chines Logs and Plywood.  Check them out, great simple design and easily understood for most of us.

G'Luck,

phil w.

Permalink Reply by Michael Rosso on July 13, 2012 at 6:41am

Kurt,

A few years ago I would have jumped at the idea of using power tools for completing something like a scarf joint.  The idea of cutting one scared me. (given the price of a 4 x 8 sheet of Meranti..)  Since then I've realized that there are some things that hand planes do better than almost anything.  My advice to you is check out eBay for a reasonable #6 jointer plane (or a #7, but that would be overdoing it a little) if you don't already have one and use it for your scarf joints.  Fletcher describes how perfectly on pg 113 of his book.     The plane will (in my opinion) give you MUCH more control, and make it much harder to screw up an expensive piece of marine grade ply.   Not to mention it'll give you a lot of practice with an invaluble tool!    Is it more work?  I suppose so.  But you could set up a router jig perfectly and if it moves just a little, it'll ruin the joint.  Same with a circular saw jig.

With regards to using the sawdust for thickener, I made the same mistake.  When you plan on making a joint and NOT painting it, I recommend using West Systems Colloidal Silica, or the 403 microfibers.

Permalink Reply by Kurt Selisch on July 13, 2012 at 8:45am

Hello guys,

Thank you so much for the advice, opinions, information, and stories of going through the same thing as I. Really appreciate your help and feedback. This is definitely a learning process. With the circuIar saw jig, I knew I would have to make a jig for 1/4 and another for 1/2 ply. However I was thinking the 1/2 ply scarf would be a 3 incher as well. But your points of the scarf needing to be 12:1 makes sense and so would need a longer scarf joint.  I did check out the router jigs, thanks guys.

I am building a 17X52 so did scarf (scarph?) an extra 15 inch piece on to the stern end of each side panel. I did not want a scarf joint in the bow, so I cut out the side panels first. Those joints came out much better than the first attempt. Thank you Michael for the advice on West Systems Colloidal Silica or 403 microfibers as epoxy thickener instead of sawdust. A clear thickener makes alot more sense.

I think I will continue with the belt sander / orbital sander method since I only have a couple more plywood scarfs to do for the bottom and am feeling a little better about what I am doing. I will need to scarf some 1/4 together for the rub rails, but will cross that bridge a little later. After I get the bottom panels scarfed, hopefully this weekend, I will begin running yellow cedar through the planer and start on the frames. Yahoo! Thanks again guys.

Permalink Reply by Michael Rosso on July 13, 2012 at 9:37am

Kurt,

Have fun and good luck!  This site has saved my bacon (and boat) countless times.  The people here are the best around.

Permalink Reply by Christian on August 7, 2012 at 10:19am
Yes it works I used a 10" saw with a new blade worked good on 1/2" for my bottom 12:1 easy . Make the bottom fence out of steal less chance for mistakes!

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