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3b. ScarfLOCK joining of plates in Stitch and Glue Kits

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This page is applicable for builders of One Ocean Kayaks Stitch and Glue Kits
Here is a picture of the Cirrus hull plates from a kit showing the open ScarfLOCK joint and the left plate with the joint already finished (hardly visible).
One of the nice features of this joint is not only its precision but also relative ruggedness before it is glued up. Unlike a traditional scarf cut which is rather fragile, the ScarfLOCK can bounce off the floor in accidental mishandling without harm. Even if a finger has cracked or broke, it is far easier to repair than a traditional scarf. Put some glue on the broken finger and press it back where it belongs. After sanding no one will know the difference.

Close-up of the joint lines. The plywood plates are of different color on purpose to make the joint more visible. When plates match in color, the joint is effectively camouflaged and you have to look for it on the kayak.

By the way, when you are comparing other stitch & glue kits, take a good close-up look at their scarf, just for curiosity. This will give you a great indication of quality of the kit in general. There are some kits out there where you have to trim routing tabs, actually sand the scarf contact surfaces to fit and when they do finally fit there are "non contact" gaps in the joints. Some well known kits even have plain butt joints with a back up plywood plate!

Even the narrowest plates can be scarflocked with strength. Here the plate tip is only 1" wide!
    The Cirrus kayak kit plates on the table ready for joining.
The Kayak Kit package comes with instructions and tips on gluing the joint but here is an overview. The joint is 100% ready for gluing. No sanding or other nonsense.
Use a normal water based carpenters' glue and brush it on both ScarfLOCK ends so that the contact surfaces are fully covered. Do not worry about cleaning the glue yet.
Do NOT use polyurethane or epoxy glue unless you do not care about glue stains around the joint and messy cleanup as well as longer wait time before kayak construction. Structurally, they are perfectly fine to use though.
The advantages of ScarfLOCK.
When dry, the fingers will fit together with more or less slight "slip fit" depending on humidity but as soon as you apply the glue, the plywood fingers quickly swell about 0.0015" (0,038mm) which will create an "interference fit". So, after both sides are coated, bring the plates together, engage the finger tips of one plate to the finger valleys of the other plate and press the fingers down evenly one by one.
Please, do NOT play with the plates by engaging and disengaging the fingers when DRY. It will be hard to take the plates apart and a finger breakage or plate scratching is possible. Also, this will reduce the instant locking quality of the fingers.
Keep pressing fingers until the plates are even. It will be helpful to have a nicely flat surface underneath. At this point, the plates will be basically locked but leave them sitting for a few minutes to dry before moving them.

Wipe off any glue with moist paper towel or sponge and remove any remaining water with a dry paper towel. When the joint is strong enough, insert 1/2" spacers under the plate next to the Scarflock. This will help with air circulation and drying.
The very narrow plates may use one wrap of reinforced tape to hold the edges in before the glue tacks up. This joint is only 1 minute old and the whole plate is suspended from my fingers right under the ScarfLOCK.
Same here for the heavier hull plate.
You can start wiring the plates onto the strongback as quickly as one hour or two hours after joining the plate sections but if you can wait, it will be easier to sand off any signs of the glue or raised grain after the plate is fully dry. Use 100 grit orbital sander or a sand block and sand minimally in the direction of the fibers.

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Last page update: 29 October 2013