How to fix a mortise that is too big at the base?

[Joey Stephenson]

I've found myself in the situation where I've chiseled a slight outward angle into my mortise, so when I insert the tenon, it is snug at the top, but I can wiggle it forward and backwards a bit with the tenon parallel to the plane of my body.

Should I try to glue in some thin wedges?

Or should I make a paste of wood glue and sawdust and layer it on the inside of the mortise a bit, then re-chisel it to be vertical? Would that have any strength, and would glue adhere to it once the tenon is inserted?

[Jim Morgan]

Sometimes this is done deliberately - see "fox wedging". The mortise is cut with an angled socket, and one or more kerfs are cut in the end of the tenon. For through mortises, the tenon is inserted and wedges are knocked into the kerf(s), expanding the end of the tenon to fit the socket. Closed mortises are trickier - wedges are inserted in the kerfs first, then the tenon is inserted into the mortise. As the tenon is driven home, the wedges seat in the kerfs, expanding the end of the tenon. Executed properly, fox wedging provides tremendous mechanical strength in the joint, so much that glue may be optional.

[Joey Stephenson]

Sometimes this is done deliberately - see "fox wedging". The mortise is cut with an angled socket, and one or more kerfs are cut in the end of the tenon. For through mortises, the tenon is inserted and wedges are knocked into the kerf(s), expanding the end of the tenon to fit the socket. Closed mortises are trickier - wedges are inserted in the kerfs first, then the tenon is inserted into the mortise. As the tenon is driven home, the wedges seat in the kerfs, expanding the end of the tenon. Executed properly, fox wedging provides tremendous mechanical strength in the joint, so much that glue may be optional.

Well, mine was definitely not designed for this! This is basically my first mortise, and it is not a through mortise. Just need to know what the best way, if any, is to straighten it out.

[Jim Becker]

If you feel that the gaps are too large to be dealt with merely with the glue for the joint, then glue in some strips solid material of the same wood with the same grain direction and re-cut more precisely after the glue cures. Don't do the "paste" thing. Use solid wood for fixing things in your projects.

[Jerry Miner]

+1 on Jim Becker's advice. Another alternative would be to use epoxy at glue-up, with or without a filler. Epoxy has strength in thick applications whereas standard wood glues do not.

[Jim Morgan]

Well, mine was definitely not designed for this! This is basically my first mortise, and it is not a through mortise. Just need to know what the best way, if any, is to straighten it out.

If there is enough material in the mortise stock, you could widen the mortise at the top so its sides are straight. Then glue on some material (i.e., veneer) onto the tenon & recut it to fit. It's certainly easier to clamp material onto the tenon.

[Charles Lent]

Cutting the strip to glue in might be difficult because of the angle. It should be easier to square up the mortise, whatever size it becomes, and then make and glue in pieces of wood to reduce the mortise to the size that you want, or slightly smaller. Then, after the glue dries, carefully trim it away to fit your tenon.

Charley

[John TenEyck]

Cut the mortise larger then glue in a shim and recut, or use epoxy with what you now have. Either way works.

John