Dent the Wood for Tighter Joints

We’ve all dented some important part of a project and hand to remove the dent with heat and steam. It’s a routine and and annoying fix. But what if we could use the same process to make our joinery tighter?

That’s exactly what I do with many joints in my chairs. I slightly compress the fibers (denting them) and then cause them to expand at assembly with hot hide glue.

This idea first occurred to me years ago when I wrote an article on biscuit joiners for Popular Woodworking Magazine. Some of the manufacturers of beech biscuits would compress them during manufacture. The biscuit would fit loosely in its slot until it encountered the water in the glue (modern PVAs and liquid hide glues are about 44 percent water). Then the biscuit would swell, locking it in place.

So Here’s What I Do
First I size my tenon to the mortise so it’s a little tighter than I like. The tenon should go in, but with hammer taps.

Then I fetch the secret weapon: Non-scratch pliers. These have adjustable jaws that are 1/2” wide. With this tool I can gently – gently – compress the fibers without tearing them, like serrated metal-jaw pliers are wont to do.

How much do I compress the joints? At this point the tenon should go in with hand pressure – like a typical well-made tenon.

Add the Glue
You can use any glue to assemble the joint. I prefer hot hide glue because the results are instant. I put glue in the mortise, paint a little on the tenon and immediately knock the tenon home. The heat and water swell up the tenon and lock it. Hard.

I have never split the work using this method. The only result is joints that are unusually good.

Give it a try before you take a potshot at the method.

— Christopher Schwarz