Broken Floating Tenon - Need Advice

[Mike Pittenger]

I think I screwed up bigtime…
I’m trying to finish a blanket chest for a wedding. It uses floating tenons. Apparently when cutting the hinge mortises I applied too much force and snapped an upper tenon (see pics). Both the leg and the rail are hickory.
Any suggestions? I would love to not have to disassemble the whole thing.
Thanks!

[johnny means]

My first thought is, what's wrong with your construction? A loose tenon shouldn't brake that easily or in that manner. Does the tenon's grain run parallel to the joint? At this point I would just epoxy it back together.

[Jason Beam]

Which way is the grain on those tenons oriented? It looks like it broke so cleanly that I feel like the grain is running parallel to the break .... which is the weakest orientation for a floating tenon. I can't imagine any wood that'd break so cleanly if the grain were oriented across the joint (horizontal in this perspective).

If that's true, and all the other floating tenons are oriented like this, you probably should take it all apart and re-orient those tenons or the whole structure is in question, IMHO.

[Thomas S Stockton]

Mike
I think the biggest problem is that the grain is going the wrong way on the tenon, for it to shear like that the grain seems like it is going vertical and should be go horizontal for maximum strength.
How I would try to fix it is to pull the entire rail off If possible and clean out the mortise in the leg. Then clean out the rail mortise and extend it into the groove. You can then make a tenon that will go into the leg and stick out however much you need. The rail can then be slid over the tenon from the top and the fix should be hidden.
Good luck
Tom

[John TenEyck]

What Jason said. Sorry, but if all those tenons have their grain oriented the wrong way there are sure to be more failures in the future, like the first time someone sits on it. The good news, if you can call it that, is that it shouldn't be too hard to fix. I suspect if you pad the rails, put a block of wood on top of the padding, and give them a good whack near the joints, all those other tenons will break as easily as the first one.

John

[Peter Quinn]

I can't imagine how you could break a long grain hickory tenon with a sledge hammer let alone chopping a few hinge mortises. The grain should always be long grain and should run parallel to the rails. If it is otherwise I would break the rest of them and start over.

[Jim Matthews]

You need not disassemble the entire chest.

I would guess that you'll need to cut the four
tenons on that same side, to remove the side assembly.

The four tenons should be removable with the same router
bit that was used to cut the mortises.

What glue was used?

[Mike Pittenger]

Thanks everyone. This was my first time using floating tenons and didn't even think about the grain (since it's done automatically when you use regular tenons). The top rail came loose easily and the other tenon was correct. To check the other 14 tenons will require disassembly. I would hate to have it fail the first time my nephew-in-law sits on it...

[johnny means]

I always say that a little bit of knowledge can be a dangerous thing. It's somewhat surprising that a piece that nice, using somewhat advanced techniques, executed fairly well would contain such a rudimentary mistake. Mike, you did a really nice job of milling and constructing the joints while not really understanding how the joint works. I'm sure it seems obvious now, but it's strange how sometimes we can overlook the simple things while lost in the intricacies.

[Andy Pratt]

Mike, don't let this discourage you: you have done really nice looking work and you will now never make this mistake or ignore grain direction in the future again. That lesson is worth something, and you can still salvage what you did. That being said, you did make a fundamental mistake that has seriously undermined the strength of your joinery.

At this point you should really count your tenons as worth next to nothing (maybe 10-20% of what they should be) strength-wise. If you don't want to scrap the project you need to reinforce every joint that might be relying on one of them.

You could do this in a few ways:
1) most simple: add large 90 degree angle brackets to each inside corner, top and bottom. This is the least elegant solution but you could make it pass by buying thick brackets (maybe brass?) and using them as the holders for a shelf in the top and a false bottom in the bottomn: "look, I made you a secret compartment" This is not a fine woodworking solution but it works if you are in a time bind and probably holds up ok over time.
2) Make a box insert for the entire inside and hide it on the top opening with flush-fit banding. If you do this you must make sure you attach it in only the right areas for wood movement or it could also ruin your piece. If done right no one would ever know, and it makes the chest feel heavier/more substantial.
3) wrap the exterior corners in something cool like blacksmithed angle brackets, reverse option of #1 at much higher cost but more cool factor

If none of these work: do whatever you can to this to make it look gift-worthy and explain what happened in the note with it, and replace it with a better made version as soon as you can, cannibalizing any parts you can for the 2nd version.

[Jim Matthews]

At this point you should really count your tenons as worth next to nothing (maybe 10-20% of what they should be) strength-wise. If you don't want to scrap the project you need to reinforce every joint that might be relying on one of them.


2) Make a box insert for the entire inside and hide it on the top opening with flush-fit banding. If you do this you must make sure you attach it in only the right areas for wood movement or it could also ruin your piece. If done right no one would ever know, and it makes the chest feel heavier/more substantial.

That's clever, right there.

[Frank Drew]

Mike,

Think of it this way: there are no failures, only more data.

If it's possible that some of the other tenons are the same as the one that broke, your best course will be to take the chest apart and redo.

[Mike Pittenger]

OK - disassembled the chest and found 3 more misaligned tenons. Got it all put together and delivered last week (pics below). Thanks for the help, everyone.

MikeIMG_1980.jpgIMG_1981.jpgIMG_1979.jpg

[Bruce Page]

That turned out very nice.

[Dave Ray]

Looks great Mike. You gave us all a reminder concerning joint construction with this project. Thank you.