Help with adjusting a mortise...

[MikeH]

Many of you have been looking at my Workbench base WIP thread. I finally got the mortises finished on one of the feet and when I put the second one in it is a little out of square.

See the pic below:

Is it better to leave the integrity of the mortise and tenon alone and gently coax everything square or should I adjust the mortise and shim the tenon? Since the through tenon won't be seen this might work.

Please let me know what you think.

Thanks,

 

[tom hintz]

Being a through tenon, its very easy to shim that, get the fit you need and retain virtually all of the strength. The fact that it is a hidden part of the project would make this my choice for fixing the problem.

 

[MikeH]

If it was mine I'd want to make it square.

I do too. I just don't want to compromise the integrity of the joint.

 

[bman]

I would think that if you don't get it square now you will be fighting it all the way through the project :BangHead: i would shim as necessary.
Barry

 

[Ray Martin]

I think I'm going to keep it unanimous. Keeping things square is important. If you make allowances for out of square here, you'll have to make (like) allowances through the rest of the project.


Ray

 

[jeff...]

why not just put that upright on the TS set the fence and the blade height to leave 16th of an inch, kerf the two outer boards and remove the 16th of an inch with a chisel to make the the outer boards even but leaving the center board intact? A I thinking to much into this?

BTW nice looking walnut and maple you got there

 

[peteb301]

Square is always best - otherwise as already mentioned - you'll be fighting it somewhere else. Fix the mortise.

 

[MikeH]

why not just put that upright on the TS set the fence and the blade height to leave 16th of an inch, kerf the two outer boards and remove the 16th of an inch with a chisel to make the the outer boards even but leaving the center board intact? A I thinking to much into this?

Not sure I understand what you're saying.

BTW nice looking walnut and maple you got there

A real nice guy in Northern NC sold it to me!

 

[MikeH]

Being a through tenon, its very easy to shim that, get the fit you need and retain virtually all of the strength. The fact that it is a hidden part of the project would make this my choice for fixing the problem.

What is the best way to adjust it? On the tenon or the mortise?

 

[jglord]

I agree with the rest here - getting it square now is imperative.

I'd start by setting up the table saw with a cut-off fence - i.e. a short fence clamped to the main fence and adjust distance from far side of the blade to the short fence to the tenon length and the blade height to trim the tenon shoulders even and square. A lot of the strength of the M & T joint comes from the shoulders sitting firmly and squarely. Then trim the tenons as needed (with a wide chisel or shoulder plane). If one side or both are loose, you can glue pieces of veneer to the tenon faces to tighten the joint. Since the veneer will not show, the variety used does not matter. After gluing on the veneer, you can gently trim the tenon to adjust the fit.

I'd also chamfer all ends of the tenon to avoid having the end-grain catch on the edge of the mortice and tearing away when fitting the pieces.

One other thing to check. If the small adjustments made to square the tenon shoulders shortens the remaining leg length, then corresponding adjustment will need to be made at the top of all other legs to ensure the top has a square base to sit on. Your picture does not show any joinery at the top, but if you plan to cut tenons to go into the table, adjust the length to be the same and then use the same set-up from above get square shouldered tenons at the top as well. From the picture it appears you will not be cutting much off the legs and should not shorten the legs much more the a sixteenth of an inch. After cutting the shoulders with the table saw, I'd use a bandsaw to cut the tenon cheeks. Cut the tenons very slightly over size and trim with a chisel of shoulder plane to get a tight fit in the top mortises. If these tenons will show through the top, don't chamfer them. You may want to slightly angle the ends of the mortice and cut slots in the tenon to allow a wedge to be driven into the visible end of the tenon to secure the joint.

You might also consider draw boring for pegs at the bottom - i.e. drill a hole in the face of the piece and mark the tenon where the hole meets the tenon, then drill the same size hole in the tenon, offset by about 1/8 of the pin size towards the tenon cheek. The pins used must be very straight grained to avoid having them break when driven in. The idea of the small offset is to have the pin pull the joint together very tightly - hence part of the need for square faces.

Hope this helps answer your question. If not I will try to clarify further.

 

[ashley_phil]

now see i'd just pound it with a hammer and sand it with a belt sander till it fit.:eusa_danc:eusa_danc

...maybe that's why my stuff looks like junk.:lol:

 

[MikeH]

I agree with the rest here - getting it square now is imperative.

I'd start by setting up the table saw with a cut-off fence - i.e. a short fence clamped to the main fence and adjust distance from far side of the blade to the short fence to the tenon length and the blade height to trim the tenon shoulders even and square. A lot of the strength of the M & T joint comes from the shoulders sitting firmly and squarely. Then trim the tenons as needed (with a wide chisel or shoulder plane). If one side or both are loose, you can glue pieces of veneer to the tenon faces to tighten the joint. Since the veneer will not show, the variety used does not matter. After gluing on the veneer, you can gently trim the tenon to adjust the fit.

I'd also chamfer all ends of the tenon to avoid having the end-grain catch on the edge of the mortice and tearing away when fitting the pieces.

One other thing to check. If the small adjustments made to square the tenon shoulders shortens the remaining leg length, then corresponding adjustment will need to be made at the top of all other legs to ensure the top has a square base to sit on. Your picture does not show any joinery at the top, but if you plan to cut tenons to go into the table, adjust the length to be the same and then use the same set-up from above get square shouldered tenons at the top as well. From the picture it appears you will not be cutting much off the legs and should not shorten the legs much more the a sixteenth of an inch. After cutting the shoulders with the table saw, I'd use a bandsaw to cut the tenon cheeks. Cut the tenons very slightly over size and trim with a chisel of shoulder plane to get a tight fit in the top mortises. If these tenons will show through the top, don't chamfer them. You may want to slightly angle the ends of the mortice and cut slots in the tenon to allow a wedge to be driven into the visible end of the tenon to secure the joint.

You might also consider draw boring for pegs at the bottom - i.e. drill a hole in the face of the piece and mark the tenon where the hole meets the tenon, then drill the same size hole in the tenon, offset by about 1/8 of the pin size towards the tenon cheek. The pins used must be very straight grained to avoid having them break when driven in. The idea of the small offset is to have the pin pull the joint together very tightly - hence part of the need for square faces.

Hope this helps answer your question. If not I will try to clarify further.

The shoulders need to be cut for sure, but the mortise is slightly off. I don't think the shoulders are keeping the leg from being square. I will cut them first to make sure they are all even and square and try it again. I'm already planning on using pegs to draw the tenon tight.

 

[jglord]

With laminated build shown you shouldn't need to adjust the mortises, but I'll believe they are off. You could adjust the mortises with a chisel, but it would be difficult to get such deep mortises exactly right. I'd stick with adjusting the tenons, if possible, and leave the mortises as they are. :eusa_thin

 

[MikeH]

With laminated build shown you shouldn't need to adjust the mortises, but I'll believe they are off. You could adjust the mortises with a chisel, but it would be difficult to get such deep mortises exactly right. I'd stick with adjusting the tenons, if possible, and leave the mortises as they are. :eusa_thin

John the good thing is that they are through tenons. I can access the mortise from the underside. :-D