We all make mistakes from time to time, some of us more than others. There's nothing more frustrating than the job going wrong when you have invested many hours of work and committed expensive materials. Well, don't despair, there's often a well-tried escape route which lets you recover the situation. And if you're careful, only you need know that it nearly went wrong. This article sets out a few fixes that have worked for me - they are as much a part of my toolkit as my planes and chisels.
Mortise and tenon joints are great for doors, chairs and tables. But to work properly the joint needs to be tight - the tenon should be a push-fit in the mortise and should hold under its own weight. A loose fitting joint will not be strong and may not glue up satisfactorily at all. The problem can come from the tenon being cut too thin, the mortise being cut too wide, or both.
Add veneer strips
There's a quick fix for this problem. You can add to the thickness of the tenon by gluing on a strip of veneer. You need the veneer to be thick enough so that the tenon is too thick to fit the mortise. Then, the over-thick tenon can be trimmed back with a rebate plane until it is a good fit. I use a small Stanley 92 rebate plane for jobs like this and find it ideal for this small-scale precise work. Depending on the exact nature of the problem, you might need veneer on only one side of the tenon, or maybe on both sides.
“You can add to the thickness of the tenon by gluing on a strip of veneer”
The photo sequence shows a poorly fitting tenon being fixed by gluing on a veneer strip on one side only. The gap has been exaggerated here to demonstrate the problem and the solution. Typically, the error will be less extreme. This quick fix recovers your joint pretty effectively, and it's completely invisible. A word of warning, though. When you are trimming the tenon, check regularly how its going. It's very easy to over-trim and leave yourself back where you started. I know, I've done it!
Other bad fit tenon problems
Mortise and tenon joints can be tight fitting but still be unsatisfactory. If the tenon is not completely parallel to the length of its timber stock, or the mortise is not totally vertical, the two pieces of timber will not come together squarely. Similarly, if the tenon (or mortise) is not parallel to the face of the stock, there will be big assembly problems. A door frame with joints like this will be warped.
Luckily, there's a solution to these problems that's a variant on the veneer patches. The thickness can be increased with veneer and the tenon re-shaped with a block plane to correct the misalignment, as shown in the diagrams. Again, be careful with the trimming and check regularly.