View Full Version : Scarph Glue-Up Jig

Clinton B Chase
06-29-2007, 02:18 AM
I wondered if anyone has a reliable scarph glue up jig plan or pic you'd be willing to share. We are glueing up 60+ planks for Compass Project's annual boatbuilding festival. I tried using bar clamps with edge clamps pressing down on the joint but it did not work. I am picturing a 2 x6/2x4 frame with wedges pressing the scarph joint together.



Jim Ledger
06-29-2007, 04:37 AM
What kind of glue? Epoxy is easiest as you don't need a lot of pressure.

Clamp the pieces in alignment on a 2x plank wider then the glue up. wax paper above and below the joint. A 2x softwood pad on top of the joint with a few C-clamps.

For 60 pieces use fast hardener and get a few going at once.

Tom Hoffman
06-29-2007, 05:59 AM
When I needed several 20+ ft. long boards for gunwales and for extra strips for my Whitehall, I first made a scarf cutting jig for my radial arm saw, that would cut aproximately a 12' long scarf in a 1" thick board. I mounted a pair of 2X10 along a shop wall for a total length of approximately 28 feet. Like a big shelf along a bare stud wall of my basement center wall I shot on a temoprary back splash just a little higher than the board I wanted to glue up and hold.

I then covered the spot where the glue up would be with Saran Wrap Laid the two mating scarfs together using Titebond III wood glue (suppose to be waterproof) could use Flag Epoxy for glue up. Then it was just a matter of clamping all together using spring clamps clamped down over the board and the back splash.

Here is a link to my scarf cutting jig.



Clinton B Chase
06-29-2007, 06:50 AM
I don't think I was clear...I need a glueing jig -- not a cutting jig -- for clamping 2-4' wide plywood scarph joints together but using no screws only clamps/wedges/etc and epoxy. TX.


Jim Ledger
06-29-2007, 07:06 AM
How about something like this.

Two sawhorses about 6' apart.

Between them lay 4-8' 2x4s on edge. About 12" apart

Level everyting up.

On top of the 2x4s lay 3 or 4 sheets of flakeboard.

This will provide a nice heavy level surface to clamp your ply to.

On the top of the joint use a heavy caul with a slight belly planed in lenghtwise.

Two clamps, one at each end of the caul should give a nice even pressure. You could vary the amount of belly in the caul to adjust the pressure.

Don't forget the wax paper.

Bob Smalser
06-29-2007, 07:30 AM

A permanent jig is easily made from a rectangular frame of flat 2X10 or 2X12 stock dovetailed at the corners, with a line of veneer press screws across the top.


06-29-2007, 09:15 AM
I cut my scarfs with a 1/32" shoulder, this allows them to align perfectly when they are glued. I pin nail them 1/4" from the sheet edge and just apply thick flat cawls the full width of the scarf; on a flat surface of coarse, and lots of weight. I happen to have a dozen chunky soup cans full of lead at 14 lbs. each. Plus old car batteries etc. With epoxy (cold cure - long open time) you dont want a lot of preassure.

Tom Hoffman
06-29-2007, 11:42 AM
I gave you the gluing jig. It was the two 2X10 set up like a shelf with a back splash, because it was on a bare stud wall, you could use the back splash to clamp to and the shelf held everything in alignment and several spring clamps left and right of the scarf hold everything in place with no slippage. Then apply several spring clamps directly on the splice. No need for nails. Everything stays in alignment because it is held up by the shelf on the same plane and the scarf is held in alignment by the back splash board. It works very well.

Tom Hoffman
06-29-2007, 11:45 AM
My mistake, I thought you were clamping dimension lumber, not plywood.

Osborne Russell
06-29-2007, 02:24 PM
Two variations on the jig suggested by Bob Smalser:

1. Join two lengths (e.g. 2x 4's) one atop the other with those sheet metal strips with holes already in them, or drill your own; then use pairs of wooden wedges for clamping pressure. They spread upward against the 2 x 4's which resist it and transfer the pressure downwards. Pro: cheap and simple. Con: fiddly.

2. Instead of wedges, thread the cross-bars and make wooden screws. Pro: excuse to buy more tools, cheaper than veneer press screws, less fiddly. Con: you have to use good hardwood for the crossbars and screws.

I usually just use weights -- bags of cement, buckets of laundry detergent, rocks, and long sticks running alongside the workpieces to keep them aligned. But then how do you fix them in position while placing the weights? Get the whole mess off the ground on sawhorses or functional equivalent and you can clamp the sticks to the horses, but then the weights make the workpieces sag. So you put them atop long 2 x 4's or functional equivalent bridging the span between the horses.

The fundamentals are support from below and lengthwise alignment.

Probably easiest of all, with thick enough pieces, is a board atop and across the scarf and one below, both on waxed paper or plastic, screwed together through the workpieces.

06-29-2007, 03:03 PM
I have made a lot of plywood scarf joints…
There was an evolution through the years,
and at first when Weldwood glue was the norm we used a large steel fixture.
This was big, heavy and unreliable as the clamping pressure required was huge.
Then, as epoxy gained trust and acceptance we used the same fixture.
Eventually, because traditions die hard in boatbuilding, we realized that clamping pressure was no longer an issue we did this;

Cut the scarf joints (by hand with a power plane/sharp #5 plane to pencil lines) primed them with epoxy,
and waited a bit (there is a lot of end grain exposed)

Recoated the joints (both pieces) with slightly thickened epoxy.

Then, assembled the pieces to the pencil lines and using some plastic visquene sheets top and bottom and backing up the joints with some ¾ inch ply, we simply screwed the pieces together with grabber screws, on maybe 4" centers
Often this was done in place, on the boat, with no unfairness

After the glue kicked off the srews were removed and the holes plugged with thickened epoxy
This method has proved 100% reliable.
I use West system because of sensitivity issues with other brands.