What you need to know about “Mortise & Tenons”

Everyone pretty much knows how to fit a Mortise & Tenon joint together but in case you don’t or forgot here’s how it goes when you push a tenon into the mortise it should just slide in with a slight bit of friction, if you need to force it, it’s too tight and if it can move side to side or if it wiggles it’s too loose. How you glue it and clamp it is just as important and maybe more the first thing I like to do is put a 1/16 chamfer around the end of the tenon so it helps guide it in now you’re ready to glue.

Place a bead of glue around the inside of the mortise just inside then use a small dowel to move the glue around the inside wall after the glue is spread around start applying glue to the tenor starting with the end grain then use your glue brush to cover the cheeks and sides of the tenor then fit it into the mortise. It’s important to use this method for two reasons one it keeps it neat and minimizes the chance of getting glue on the outer surfaces and number two it prevents the joint from future failure. Here’s the reason behind this theory, when you push the tenon in the glue is pushed to the bottom of the mortise and absorbed into the end grain pulling as much of the glue into the fibers as it can and thereby absorbing the glue that should be left behind to give strength to holding the cheeks so but applying glue to the end of the tenon the fibers get all the glue absorbed before it can be pulled from the sides of the tenon. Now comes the clamping, after the joint is closed all you need is ¼ to ½ turn on the clamp if you have to tighten it any more then that something’s not lined up correctly or the Mortise & Tenon is too tight. As a side note when edge gluing two board all you need is enough clamp pressure to make the boards touch so the seam is gone then all that’s needed is about ¼ to turn this should give you about 40 Pounds of pressure at the joint for a 4/4 board but when gluing thicker boards you need a little more clamping pressure so for 5/4 I like to see about 50 psi or ½ turn and 8/4 I go to 60 psi ¾ to on full turn.