Well I Took The Plunge

[Malcolm McLeod]

This is a sample of a bar stool. If you sit in the chair and "lean" back on two legs, where would your stress point be? It's the same with any chair, there are stress points. First we thought it was insufficient glue, testing a few loaded with glue and dried it was better, but not 100% safe. If a reasonable amount of effort(stress) went into the chair the joint would break. So extra reinforcement was added to help the Domino from separating under stress.

We treat our own chairs different than a customer.

Jack,
I suspect anybody who's ever fixed a chair knows where the stress concentrations are, but again how did your stools fail...? You seem to be saying the glue itself failed in first iterations (suspected to be glue-starved). With a well glued joint it was better, but did the glue still fail or did one of the joint elements fail? i.e. Tenon crushed? ...Mortise blow out?

Sorry to hijack the thread, but I are a enjinear - and just trying to understand.
Thanks,
Malcolm

[Tom Ewell]

I vaguely remember Jack's earlier posts on this topic and don't recall any actual design elements being offered there either.. (might be wrong tho maybe I'll look it up)

In the early '70's I was in the night club business, both building and running.

Seating furniture had to be maintained to mitigate normal wear and tear, especially the 'loose' joints.

Most times it was simply a matter of retightening the mechanicals, maybe injecting some glue and/or reupholstering seat covers. I do not recall any pieces that relied solely on glued up joinery at the heavy stress points in that commercial furniture. If a glue joint separated (regardless of type) the mechanicals held it together and merely yielded a 'wiggly' chair or stool which hopefully would be noticed before failure and gone back to maintenance.

I suspect that Jack's reference to 'extra reinforcement' includes this mechanical support, which probably should have been done at the outset instead of assigning blame to the choice of joint.

[Martin Wasner]

I suspect that Jack's reference to 'extra reinforcement' includes this mechanical support, which probably should have been done at the outset instead of assigning blame to the choice of joint.

Wouldn't that be the same as saying the joint isn't good enough for this application? Which is exactly what Jack was saying from the get go?

[Tom Ewell]

Wouldn't that be the same as saying the joint isn't good enough for this application? Which is exactly what Jack was saying from the get go?

Yep and he had to recall 700 units because of this discovery in order to beef up the joint is what I take from this discussion.

We still don't know exactly how the joint was fitted glue to wood wise, I was just suggesting that perhaps the original design should have had the beefed up parts, hard lesson to learn and I laud him for putting out this info.

[mreza Salav]

Wouldn't that be the same as saying the joint isn't good enough for this application? Which is exactly what Jack was saying from the get go?

Martin, if you go back and read my post #39 that would help. My claim was (and still is) domino vs. traditional M/T comparisons are valid if you are talking about the same size in both.
If we agree with that, this example proves nothing about whether domino is better or worse vs traditional M/T.
The point is, if the joint requires you to use a big tenon (not provided by domino) you have to use proper size tenon so your option is a M/T. If the joint is sufficient with a smaller tenon
then there is no difference using a M/T or a floating one. I wouldn't call M/T a better joint in that situation.
We are still missing details on Jack's situation (what were the leg/apron/tenon sizes, number of them, etc); it could be the tenon wasn't sized properly or simply the joint is under more stress than
a tenon can handle...

[jack duren]

When the chairs were introduced to me I suggested M&T as for one I never used a domino to start with and secondly I didn't trust it for the application. My suggestion was declined and they wanted the chairs moved off to a production so anybody in the plant could produce them based on my configuration.

My negative post isn't because I dislike the Domino, but rather to suggest that you cover all bases with its use in stressful joints because it can fail.

mreza Salav's ....A M&T has one point of failure where a Domino can have two when it comes to glue. You'll get better odds if you only have one...

[Larry Edgerton]

From my own experience a Domino in the end of a rail such as would be the case in a chair is not anywhere near as strong as a tenon cut out of the wood in a traditional fashion. In my tests for my own satisfaction the rail breaks around the Domino if the domino is as big as a tenon would be. I seldom agree with Jack about much, but in this one case I have to agree. If the rail was larger where the Domino mortise was not such a large percentage of the cross section it would not be a problem, but you can not make parts big just because you want to use a particular machine, at least not in my world.

I have however cut the mortises in the legs with a Dominoe and then cut tenons in a traditional manner on the stretchers, just squaring the edges in the dominoed mortises with a sharp chisel.