Festool Domino Strength

[Ed Gibbons]

How do the Domino joints stand up to standard mortise and tenons, biscuits, etc?

[Brice Burrell]

How do the Domino joints stand up to standard mortise and tenons, biscuits, etc?

This has been hotly debated. Several mags have done testing and the results weren't great, not bad either. In practice most users swear by the strength when used correctly. I've been very happy with my Domino but I admit I've not done anything to really challenge the strength of the joints.

I'm sure you'll get a lot of opinions shortly.

[Mike Henderson]

My belief - not based on any scientific tests - is that a regular mortise and tenon is stronger than a loose tenon. But for almost all applications, both are plenty strong enough. The advantage of the Domino is speed in building, which is important for people trying to make a living from woodwork.

Mike

[Bill Orbine]

My belief - not based on any scientific tests - is that a regular mortise and tenon is stronger than a loose tenon. But for almost all applications, both are plenty strong enough. The advantage of the Domino is speed in building, which is important for people trying to make a living from woodwork.

Mike

Mike Henderson said it........ choose the joinery appropriate to the job. When it's good enough, enough said! The domino is excellent for frames, small doors and some funiture joinery... It isn't everything but it many things.

[glenn bradley]

If you are trying to rationalize spending what a Domino costs I would look at production speed and repeatability for specific joints vs. being able to say "its stronger than the XYZ method". Wood and FWW have done multiple joinery stress tests with surprising results in some areas and expected results in others based on what I expected.

There is a lot of discussion regarding those tests here and on other forums. All in all I try to use appropriate joinery for the task at hand and (thanks in many cases to help from the good folks here) have never had a failure with M&T, floating tenon, biscuits, dowels, pocket holes, drawer lock, etc., etc., etc. Use an appropriate joinery method and I think you will be happy.

If you do a lot of joints that a Domino excels at, I would get one. I had a biscuit joiner and rarely used it and so sold it. Your mileage will vary. I do few dowels so doing it without a jig works for me. I do a fair amount of M&T and floating tenon work so I did spring for a Mortise Pal and enjoy the ease and speed of using it. Slam-work I do with pocket holes and enjoy the ease and speed. Larger, aesthetic or 'heirloom' work I do 'old school' with hand fit M&T.

[Rick Fisher]

I have a floor model mortiser and a domino..
I use the domino .. 20 x more than the mortiser..

I have used the domino for attaching aprons to legs, no problem.. I have never had a domino joint fail..

There are times however where you just know that you should make a conventional mortise and tennon..

[johnny means]

I borrowed a friends domino jointer once in order to build up four complex face frames each requiring 54 tenons. I can tell you the joints wer strong enough that i sorely regretted dry fitting everything. I can't imagine anything short of catastrophic failure of the rails and or styles would ever allow any movement in these joints.

I believe the actual joint made by the Dominoes is just as strong if not stronger (due to the precise fit) than a traditional mortise and tenon (assuming tenons of similar size). That being said, it seems to me that having two mortises instead of one does create two possible points of breakage thus increasing the odds of failure due to splitting of the joined pieces.

IMO Domino joints are plenty strong for anything I'll ever build(and I build children's furniture).

Not to mention i was able to mill and glue over 200 loose tenon joints in just over 12 hours (my typical workday). I had already allotted and billed for a solid weeks labor for this task. If the Domino had cost me $2500, it would have paid for itself that day. I have not purchased one yet, but the moment I get another job requiring mortised joints I'll be off to Woodcraft to buy my own.

[Steve knight]

I get a kick out of people who say they have not had a failed joint yet. have you tested that joint to the fail point? have you had the piece for 30 years? moved it around to places with different humidity levels?

[Mitchell Andrus]

I get a kick out of people who say they have not had a failed joint yet. have you tested that joint to the fail point? have you had the piece for 30 years? moved it around to places with different humidity levels?

My teeth haven't fallen out yet either, nor have a I flown by flapping my arms.... yet.

I agree Steve, it's a stupid way to qualify a trusted belief.

Loose tenon joinery has been around for centuries. A new method of cutting the mortises doesn't make it a "new" nor untested method. I've done over 150 cabinet doors with domino joints and haven't had a failure - yet. Before that, over 300 doors with dowels... not one failure - yet.

I'd be better to examine the glue than the mechanics of the joint. If the glue fails, the mechanics regardless of method is largely irrelevant except if you've drilled and pegged where glue is now the redundant element and method becomes critical.

Most joints don't "fail". A joint gets busted because of a force outside of what's considered 'normal' and expected under regular, proper use. I can't imagine opening and closing a cabinet door with such force that a loose tenon joint would fail.

Sliding a heavy table across a floor might be normal - but if the builder doesn't consider the forces and build his joints accordingly, he's executed a poor design. In this case, I wouldn't blame the joinery, I'd blame the designer.

We aren't failed by the joint. We're failed when the wrong joint is used.
.

[Joe Spear]

[QUOTE=Mike Henderson;1212731]My belief - not based on any scientific tests - is that a regular mortise and tenon is stronger than a loose tenon.


I've heard that opinion before, but I wonder about it. Why would a loose tenon, properly sized and glued, be weaker than an integral tenon?

With a regular mortise and tenon joint, one end is glued into a mortise the same as a loose tenon. Therefore the strength should be the same on that end for both types. The other end of a loose-tenon joint also has a glued-in tenon instead of a tenon shaped from the board itself. The strength should be the same on that end of the joint as that of the integral tenon in the mortise.

If the joint fails in tension (that is, being pulled apart) that would be because of a glue failure, not a breakage of the tenon.

The tenon should not fail at all in compression in the direction of the tenon grain. (Of course, with several tons of pressure, the wood would be crushed, and you would have to make a new piece anyway.)

That leaves us with a sideways force, for example, if I throw my 250 pounds onto a very small table and break the tenons holding the apron pieces together. It is generally stated that a proper glue joint is stronger than the wood itself. So wouldn't a loose tenon joint, properly glued, have the same strength as a conventional mortise and tenon joint?

When the table breaks down with me on it, if my force exceeds the strength of the tenon, the tenon will crack whether it is a loose one or an integral one. I don't see that a tenon shaped from one board will be less likely to break than one inserted and glued into a mortise in that board.

Maybe an integral tenon is stronger than a loose tenon, but I can't see that. And anyway, as many people have said, after a certain point, strong enough is good enough.

[Chris Friesen]

I've heard that opinion before, but I wonder about it. Why would a loose tenon, properly sized and glued, be weaker than an integral tenon?

In many cases a loose tenon works fine. But not always.

Consider the pathological case. A slat 5/16" thick with a 1/4" thick tenon going into a 3/4" rail.

With a loose tenon, your mortise walls on the slat are 1/32" thick. Those are going to be hard to machine accurately. Then, since endgrain doesn't glue well, at the base of the mortise in the slat those skinny walls are going to be taking most of the stress of the joint.

[Chris Tsutsui]

There was an actual unbiased test in a woodworking magazine where they measured in pounds, the force it took to break various types of joinery.

A mortise and tenon joint was slightly stronger than an equivalent domino joint.

M&T > Domino > 2 dowels > biscuit

All assembled with the same wood, wood glue, and procedure.

Anyone have a scan of that article, it's been months since I read it?

[Mike Henderson]

[QUOTE=Mike Henderson;1212731]My belief - not based on any scientific tests - is that a regular mortise and tenon is stronger than a loose tenon.


I've heard that opinion before, but I wonder about it. Why would a loose tenon, properly sized and glued, be weaker than an integral tenon?

With a regular mortise and tenon joint, one end is glued into a mortise the same as a loose tenon. Therefore the strength should be the same on that end for both types. The other end of a loose-tenon joint also has a glued-in tenon instead of a tenon shaped from the board itself. The strength should be the same on that end of the joint as that of the integral tenon in the mortise.

If the joint fails in tension (that is, being pulled apart) that would be because of a glue failure, not a breakage of the tenon.

The tenon should not fail at all in compression in the direction of the tenon grain. (Of course, with several tons of pressure, the wood would be crushed, and you would have to make a new piece anyway.)

That leaves us with a sideways force, for example, if I throw my 250 pounds onto a very small table and break the tenons holding the apron pieces together. It is generally stated that a proper glue joint is stronger than the wood itself. So wouldn't a loose tenon joint, properly glued, have the same strength as a conventional mortise and tenon joint?

When the table breaks down with me on it, if my force exceeds the strength of the tenon, the tenon will crack whether it is a loose one or an integral one. I don't see that a tenon shaped from one board will be less likely to break than one inserted and glued into a mortise in that board.

Maybe an integral tenon is stronger than a loose tenon, but I can't see that. And anyway, as many people have said, after a certain point, strong enough is good enough.
There was a good paper in an early FWW magazine by Bruce Hoadley (the wood expert). His analysis of joint failure was that the wood that the glue is attached to is what fails in a joint, not the glue. So if one end of a M&T is glued and the other "end" is natural wood, there's less place to fail.

There's not a lot of literature on real joint failure (where the joint comes loose and not where something breaks) so it's hard to come to any real conclusion.

Mike

[Ed Gibbons]

I have made several mortise and tenon joints. However, none have been perfect. There always appears to be a little extra space between the tenon and the mortise. If the domino works as advertised, the result is an almost perfect fit. So, a domino joint for most of use, is stronger (and certainly quicker to make) than the typical M&T joint we make.

[Mike Henderson]

I have made several mortise and tenon joints. However, none have been perfect. There always appears to be a little extra space between the tenon and the mortise. If the domino works as advertised, the result is an almost perfect fit. So, a domino joint for most of use, is stronger (and certainly quicker to make) than the typical M&T joint we make.
That depends on what glue you use. Epoxy is gap filling and very strong even when filling gaps. Also, some of us make tight M&T joints (at least some of the time:)).

The big advantage I see for the Domino is speed. And it's generally strong enough.

Mike

[Leo Graywacz]

No fair comparing a sloppy M&T to the Domino and expect a comparison. Apples to Apples. The M&T must be constructed properly.

[Cliff Rohrabacher]

It is surprising what that little biscuit tool can do.

Dowels too are often stringer than they get credit for being.

Do a search on the Creeker's name
David Dundas
and look at what some of his delicate looking joints are doing. He posts lots of pics

[Joe Spear]

[QUOTE=Chris Friesen;1213921]In many cases a loose tenon works fine. But not always. Consider the pathological case. A slat 5/16" thick with a 1/4" thick tenon going into a 3/4" rail.


That really is a pathological case. I surely wouldn't be brave enough (or steady enough) to try that.