I new way to scarf? Any thoughts?

A

Andrew Holley

Well-known member
Last year I made the Devlin Scaup, first time scarffing plywood. While my joints turned out good, I wasn't happy with the process of assembling them. Doing it alone, I found it hard to keep the edges straight and the joint even in thickness to the plywood.

I am getting ready to start building another boat (one of my own design, sort of) and thought it might be easier to make a "stepped" joint. Total length of the joint would be 6 inches so I would end with just marginally less surface area in the joint for glue, with two steps, in 1/4" incraments, three inches wide each. I would use a router to remove the water material and should end up with a joint that is easier to push together and self aligns the edges. I would think the strength of the joint should be the same as a regular scarf.

Hopefully I explained this enough for you to understand, I tried coping a drawing from Word, but it doesn't show up.

Any thoughts?
 
I'd be more concerned that the long edges of the scarfed panel are straight. I made a cradle and then on one side, I turned a 2x6 on it's side..I snapped a chalkline on it to line up the sheets while gluing the scarf. I eneded up with perfectly straight 16' panels so the offsets of the pattern were right on the money. I think a stepped rabbit would be pretty strong as long as it wasn't at a severely tortured area on the hull. My thinking is, you will have less plies at each point of the scarf rather than all plies continuing end to end as in a regular scarf ..hard to explain but can you see my thought?
 
Andrew,

I agree with Lee, I think the joint woudl be strong in terms of pulling, but I think it ouwld be weaker than a scarf if you twisted or bent the panels along the long axis.

In scarfing I just clamped the panels to a alum straightedge and screwed through the joint to hold.

T
 
I'm an expert. Because I screwed up my first scarf ; )

The second time around it came out perfectly. I built a 16' long table using the lumber that was later recycled for the boat cradle. In essence I created a 16' long work bench. The "table" was the 3/4" ply that didn't need to be scarfed.

I then put the 3/8th on top of the 3/4" inch sheets. Very level and solid.

Once the planing and scarfing was done, I set the pieces up to scarf. I placed the first 16 footer on top of plastic, then a piece of plastic on top of the first. The second 16 footer was placed directly on top of the first, again a layer of plastic was placed.

I then squared up all using a straight edge. Then I placed six solid cement blocks (5-6" high I think) on top of the pile. Then I applied the straight edge to double check the whole pile. At the time it was cold out so I built a tent of plastic and put a bulb in there. I used slow hard.

Perfect scarfs. Can't wait to see pics of your new design and boat Andrew, good luck.
 
almost forgot. I clamped the ends of the scarfed pieces to the "table" so they wouldn't slide away from the joint.
 
I tacked my sheets to the chalk line, then stapled the scarf with 1/4" staples..put a sheet of wax paper over it and did the same with the other 16' sheet..clamped a 2x4 flatways across the sheets with another 2x4 with a VERY slight radius on top of it to give even pressure all the way across. Perfect joint
 
Andrew

I used a half lap joint on my son's boatbed. I cut it 6" wide on the router table which required multiple passes. The advantage, assuming you have the tools to make it accurate (constant depth of cut, shoulder square to plywood edge), is each piece has a shoulder that makes it easier to keep alinged during the bonding process. The disadvantage is it's not as strong as a scarf joint. I think Joel Mill at Devlin uses a half lap, 8" or longer", on small boats because the joint is easier to hide and a bit cleaner. Me, I'd stick with a scarf joint on a bigger boat. Lee is correct, you want a straight edge along the plywood when you are done since this is the basis for your offsets. Of course I guess if someone didn't keep their lines straight they could always drawn a stright line on the plywood and use that as a reference.
 
I stuck to the old tried and true method. Started last night about 7, by about 9:30, I had 8 sheets scarfed, with two sheets done on both ends. I started using my circular saw with a homemade scarffing jig, then switch to just using the 3 1/4 hand planer, a little messer, but easier and I felt safer (but man I wish I had a 6" planer)

This morning, after Church and before the inlaws, I built a rack to hold the panels and got the two sets of three epoxied and clamped up. Just barely fits in the garage (which I had to clean and move everything around).

Thanks for the advice.

Andrew
 
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