I am joining many short length strips with scarf cuts across the thickness of the strips. The scarf cuts are consistant and smooth because they are made on a belt sander. I ripped these strips a little thick since I intend to run the full lengths through the planer after joining the shorter lengths end-to-end.
My problem is with the glued joint. I tested some scarf cut/joined sample strips using yellow wood glue as well as Gorilla glue. The Gorilla glue was much stronger in the sample test, and in fact the wood strip broke during twisting rather than at the joint. However, the Gorilla glued joint is now incredibly week in my actual strips. They actually break at the joint just during handing.
Does anyone have any tips for this type of joint or specifically with Gorilla glue? My scarf cut is generous, about 1.75 inch long across the thickness. I spread a thin layer of Gorilla glue on one surface, then dampen the other surface as instructed. I cut a 0.25 inch slot in wood blocks, then slide a block over each glued joint as a tight clamp while the glue sets (wax paper prevents adhesion to the blocks).
Thanks,
Jeff
(working on a One Ocean - Expedition Sport kayak)
scarf cut strips / glue joint
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Jeff in Farmington, MI
- Posts: 118
- Joined: Wed Jul 07, 2004 3:19 pm
- Location: Farmington, Michigan, USA
I don't have experience with Gorilla glue, but from what I've read in tests, it is much more dependent on tight clamping for strength than other glues. It is not easy to clamp the scarf joint tightly. Epoxy works well.
One way to clamp is to use 3 clamps for each scarf joint. One on each side clamps the pieces to the cauls, keeping them from sliding when the clamp is applied directly on the joint. With epoxy I use spring clamps for this, and scraps of strips as cauls.
One way to clamp is to use 3 clamps for each scarf joint. One on each side clamps the pieces to the cauls, keeping them from sliding when the clamp is applied directly on the joint. With epoxy I use spring clamps for this, and scraps of strips as cauls.
Alan
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Tim Eastman
- Posts: 245
- Joined: Sun Oct 23, 2005 12:40 pm
- Location: Grand Rapids, Michigan, U.S.A.
Sounds like you did 'bout everything right Jeff. Maybe Alan pegged it on the clamping pressure. Your block system sounds very close to what I did. But I had my strips lay flat in between spacers which made up a jig that kept everything straight and flat. To clamp I used other block pieces screwed down to the spacer blocks with drywall screws. There was no question about anything moving..
I use simple Titebond II. Your scarf ratio sounds properly adequate. I've not heard of Gorilla Glue deteriorating quite like that. That's a new one to me.
Have you had any issues tooling with it? Does it sand okay without gumming things up? Does it get caught in your planes? I tried it once on a completely different project and really didn't care for it but I was trying to give it a shot.
I need to edit this reply;
Most of my hull strip splicing I am now doing right on the hull with a japanese razor saw. I just dryclamp the two pieces in line where they would naturally land as a full strip and cut them right there with a playing card (as in a card deck) under the strips so as not to scrape or damage the strips already installed in place. Saves a bit of time and the joint is cut on a scarf angle - just not as much as the 1:8 ratio. In this case I use very solid clamps in the glue-up. One on either side of the joint to keep the two strips from moving and one right on the joint wrapped in wax paper. It won't move - but even if it does the scarf type angle will hide most of the mistake. Again the Titebond II is proving itself to be adequate for this glue-up.
I use simple Titebond II. Your scarf ratio sounds properly adequate. I've not heard of Gorilla Glue deteriorating quite like that. That's a new one to me.
Have you had any issues tooling with it? Does it sand okay without gumming things up? Does it get caught in your planes? I tried it once on a completely different project and really didn't care for it but I was trying to give it a shot.
I need to edit this reply;
Most of my hull strip splicing I am now doing right on the hull with a japanese razor saw. I just dryclamp the two pieces in line where they would naturally land as a full strip and cut them right there with a playing card (as in a card deck) under the strips so as not to scrape or damage the strips already installed in place. Saves a bit of time and the joint is cut on a scarf angle - just not as much as the 1:8 ratio. In this case I use very solid clamps in the glue-up. One on either side of the joint to keep the two strips from moving and one right on the joint wrapped in wax paper. It won't move - but even if it does the scarf type angle will hide most of the mistake. Again the Titebond II is proving itself to be adequate for this glue-up.
Tim Eastman
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Be an example worth following
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Be an example worth following
Hey Jeff,
I use wedges to clamp my scarf joints. I screw 2 blocks of wood down into a piece of plywood.Space the blocks 2 inches larger than your strip width. place the strip on the plywood between the blocks and in drive a wooden wege between each block. iI use epoxy though . I have also scarfed larger stock and then ripped the strips from the larger stock
Brad
I use wedges to clamp my scarf joints. I screw 2 blocks of wood down into a piece of plywood.Space the blocks 2 inches larger than your strip width. place the strip on the plywood between the blocks and in drive a wooden wege between each block. iI use epoxy though . I have also scarfed larger stock and then ripped the strips from the larger stock
Brad
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Jeff in Farmington, MI
- Posts: 118
- Joined: Wed Jul 07, 2004 3:19 pm
- Location: Farmington, Michigan, USA
Thanks for the feedback guys!
I have since gone back to using ordinary wood glue at the scarf joint, and I have not had any strips break during handling. I am reasonable confident that they'll hold up during stripping.
I am not absolutely sure what went wrong with the Gorilla glued joints, but I agree it was probably inadequate clamping pressure. My successful initial test joints were held tight with small C-clamps, but the failed joints were held with the wooden block clamps. They probably slid apart as the Gorilla glue foamed.
Tim,
I like your process of scarf cutting strips on the mold. I am sure that I'll make use of that method during the build as well. I want to build with as many full-length strips as possible, so I am trying to mass-produce these scarf joints on the bench. I clamp the scarf-cut strips together while they are laying on edge on top of the bare strongback. That way, the strips are sure to be aligned perfectly straight.
As a side note, the reason for the many scarf joints is that I decided to build the kayak with bright white cedar (WRC sapwood) for most of the hull. Dark brown WRC will cover about 2 inches on each side of the shearline, while most of the deck will be light rosey-colored WRC. I think the extreme constrast will be striking, but the solid white WRC sapwood boards just don't exist except in 8 to 10 foot lengths. Even those usually have some knots and off color variations which I am cutting around.
Jeff
I have since gone back to using ordinary wood glue at the scarf joint, and I have not had any strips break during handling. I am reasonable confident that they'll hold up during stripping.
I am not absolutely sure what went wrong with the Gorilla glued joints, but I agree it was probably inadequate clamping pressure. My successful initial test joints were held tight with small C-clamps, but the failed joints were held with the wooden block clamps. They probably slid apart as the Gorilla glue foamed.
Tim,
I like your process of scarf cutting strips on the mold. I am sure that I'll make use of that method during the build as well. I want to build with as many full-length strips as possible, so I am trying to mass-produce these scarf joints on the bench. I clamp the scarf-cut strips together while they are laying on edge on top of the bare strongback. That way, the strips are sure to be aligned perfectly straight.
As a side note, the reason for the many scarf joints is that I decided to build the kayak with bright white cedar (WRC sapwood) for most of the hull. Dark brown WRC will cover about 2 inches on each side of the shearline, while most of the deck will be light rosey-colored WRC. I think the extreme constrast will be striking, but the solid white WRC sapwood boards just don't exist except in 8 to 10 foot lengths. Even those usually have some knots and off color variations which I am cutting around.
Jeff