Integral vs Loose (dominos) Tenons

[jussi]

On another forum they had a discussion on the Festool Domino and one guy commented that he built hundreds of stools for a chain restaurant using Dominos and they all had to be replaced. Also he had never seen an integral MT fail. I always thought that loose tenon joinery (if done correctly) were just as strong as integral tenons. If they aren't as strong, what makes the integral tenons stronger.

I have a domino and built a few things with it but nothing that had to take the abuse a chair might. I'm particularly interested because I probably will build a chair/stool one day and my thought was to always use the domino. Should I rethink this?

[meackerman]

I've always heard that a properly done loose tenon was almost as strong as a properly done integral tenon....close enough in strength that there shouldn't be any difference in practicality.

but the key is that is a properly done joint (for either type).

I wouldn't hesitant to use either type, course there are some joints that an integral tenon is the way to go.

[jteneyck]

I've never had a loose tenon fail, and I've certainly used 1000's of them by now. I built 4 of these chairs about 20 years ago.



All the key joints were done with loose tenons. The get used every day, though not hard like ones in a restaurant might.

The only difference between a loose tenon and an integral one is the loose tenon is glued into both pieces. I guess that means you have twice the probability of glue failure. However, my personal experience is that I can machine closer and smoother fitting loose tenon joints than I ever could integral ones and that is a key requirement for a strong joint.

I wonder if the failures that guy had with those chairs was because of the size of the Domino he might have been forced to use because of the design. A 1" wide tenon on a 2" wide piece, for example, would not be optimum from a strength perspective. That's one of the things I've always felt was a negative with the Domino, although maybe there are ways to make custom sized mortises with it to which you then fit a custom sized loose tenon.

John

[giradman]

Well, I would suspect that a well made 'loose' tenon joint w/ proper gluing would be pretty much the same strength - the glued portions once cured should be as strong if not stronger than the adjacent wood - typically when a tenon joint is stressed (at least on some of the videos I've seen) the wood breaks before the glued portion of the joint.

Although I have a Delta mortiser and a number of methods of making tenons, most of my joinery these days is done w/ loose tenons (using a jig) or w/ dowels (again w/ jigs) - I've also used the Beadlock system which is analogous to loose tenons and the Miller Dowel System which works well but probably would not trust w/ heavy use/loads, like a chair.

BUT, a few months ago, wife and I were vacationing in Blowing Rock (about 90 minutes from home in Winston-Salem); we were sitting at a restaurant and her chair collapsed! Fortunately, she was not hurt at all - but looking at the broken chair, the integral tenon had broken. And at a local Thai restaurant last year, she again was sitting in a chair which collapsed (again not hurt at all) - years ago, my FIL went to a home w/ antique chairs and sat on one which immediately broke (buy hey probably was hide glue?) - SO, I'm not sure that I trust those chairs - Dave

[Dave Diaman]

The guys are right. A properly made loose tenon should be just as strong as a standard M&T joint. Think about a standard butt joint. The strongest part of the joint is the glue. Now if the joints were made sloppy and the tenons did not fit tight things will change. PVA glue is not that good for gap filling so you will end up with a weak joint. Again, use epoxy instead of PVA and the joint should be fairly strong again. Most of the time I use traditional M&T joinery and pin my tenons because I am building traditional furniture and that is the way it was done. For cabinets though, loose tenons are just faster and easier for me so that is what I use. It would be interesting to see a test comparing the two joints using different fits and different adhesives. There is an article for a WW magazine. I'm sure it would be interesting. Since the Domino hit the market loose tenon joinery has become a lot more popular so it would be a pretty good subject for an article.

[meackerman]

Fine woodworking has done two articles on it.

[handi]

I always am suspicious when some says "always" and "never".

Loose tenons do represent more risk because you have two glue joints to do properly, but as stated above, done properly, there should be no discernible difference.

Integral tenons certainly CAN fail if done improperly, and anyone who says they have NEVER had one fail... Well. I have repaired many failed tenons, a few even of my own making!

I would take your friend's comments with a quantity of salt. Loose tenons have been around a LOT longer than the Domino, or even electricity.

Ralph

[Dave Diaman]

meackerman said:

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Fine woodworking has done two articles on it.

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Shows you how much time I spend reading magazines I do vaguely remember an article where they tested adhesives using M&T joints but not one comparing loose v/s traditional M&T. I'll have to see if I can dig it up in their archives.

[Dave Diaman]

I just looked and here were their results and this is assuming the joint was a good quality join. I also didn't look to see the size Domino they used. The article was in FWW #203 JAN 2009

M&T. 1444 lbs of force to break the joint
Loose M&T 1396 lbs
Domino. 597 lbs

[JR1]

A properly done loose tenon will be stronger than an integral tenon. Why? Modern glue is stronger than wood and you will have 2x the glue area in a properly built loose tenon than an integral tenon. I've seen/had Domino joints fail for three reasons: using the wrong size domino, bad design (usually more than one tenon should have been used), bad execution. I suspect that the case that you cite was bad execution or inappropriate domino size/joint design. Unless you use the Domino XL you often need to double up dominoes and even that may not work. Even the large XL Dominoes may not be big enough. Dominoes are not the answer to every joinery problem, even when a M&T joint is appropriate.

The FWW tests were flawed butt they effectively measured the area of the glue as applied, not the strength of the joint.