Gluing without clamps – The rub joint

Posted by

A while ago I read an article by Paul Sellers about spring joints. In it, he made an almost off-hand comment about the once common practice of edge joining panels without any clamps at all. Given the context of the comment, I’m not sure if this technique only applies to animal glues which, in his words, ” ‘snatched’, which meant that during the cure the glue ‘pulled’ surfaces together“. Moving forward several months, yesterday I was joining up some small lengths of Spotted Gum for tall drawer fronts, and found myself clamp-less, owing to my wife working on a large project which required most of the suitably sized clamps. Paul Sellers’ words found their way from my long term memory to my present consciousness, and a light bulb illuminated.

Now I don’t have any hide or fish glue (is fish glue even a thing any more?), so decided to attempt rub joining the pieces with plain old PVA white glue (my wife had the Titebond III on the other side of the shed, whilst the plain PVA was on a shelf right behind me – I like to think this is a sign of someone naturally operating at peak efficiency, rather than laziness).

White PVA with inaccessible Titebon III all the way over there in the background.

Before I get underway, for those unfamiliar with the rub joint, here’s Paul.

This is where we rub the two glued edges to be joined along one another moving one back and forth against the other, which is held in the vise, until the glue is evenly and thinly dispersed. During this process the glue gets as thin as possible between the surfaces and then, at a certain point, the glue ‘grabs’ or ‘snatches’ and the parts no longer move.

Leaning two or three sticks inclined and sighted in against one another (to ensure no twist in them) against a wall was a resting place for the glued boards to stand leaning in toward the wall on edge but flat against the sticks. The boards were left unclamped until the next day when full cure was achieved.

Paul Sellers, 2014 ( https://paulsellers.com/2014/10/questions-answered-spring-edge-edge-jointing-boards/ )

The panels I made up were each comprised of two boards 300 x 85 x 18 mm, with the join on the 18 mm side.

After a bit of preparation on the other draw components in the workshop this morning, I changed my mind and decided to forgo the spotted gum as the fronts. I was thus left with two panels glued up with a new method that I no longer needed. Why not test the strength of the joint.

To test, I clamped one board to the end of my bench, with the joint just proud of the edge.

But what to do for weights? Fortunately there are a bunch of dive cylinders that are currently living under the table saw wing, and being filled to 240 bar they weigh in at a nice even 20 kg each (give or take 50 g). Note the strategically placed blue matting below to cushion any falling tanks.

20 kg? All OK.

40 kg? All OK.

60 kg? Still no issues.

Oh dear, while I had more weight, there was no more room on the board to hold additional cylinders. So what to do? Fortunately there is one more heavier weight at hand.

For the record, I was wearing steel capped boots, and heavy trousers.

In conclusion, I have decided that the rub joint is remarkably effective.

Lance

October 2019

Leave a Reply

Your email address will not be published. Required fields are marked *