Domino Strength Test

[jaguar36]

I'm putting together a full review of the Domino.  One of the things I was curious about was how strong the joints actually were.  So I built a simple test rig to measure the strength of the joint, and compared it to just a plane butt joint and to pocket screws.  The rig is meant to simulate a face frame, as thats one area where I've used Dominos in the past that would be easy to test and where you could use a number of different joinery methods.  I used 5x30mm Dominos in 3/4" cherry for the test.

I was surprised to find that while the Domino did double the strength of the joint compared to just a butt joint, the pocket screws were 50% stronger than the Domino.  One commenter did point out that if strength was a major concern a longer Domino could be used, and that's a good point.  I've got some 6x40mm Dominos laying around so I'll try that out.  Still I was rather disappointed in the Domino as I thought it would be just as strong if not stronger than the pocket screws.

Here's the video I made of the test:

 

[Roseland]

You might be interested in this video, from Paul Marcel:
=youtu.be

Andrew

 

[GarryMartin]

If you search for domino strength on YouTube you'll see quite a few different reviews testing different scenarios. It's good that you've added another, but it would equally be interesting to find whether your results match others or are at odds with them.

Have you reviewed other examples?

 

[antss]

Few observations / comments:

The domino you used is a bit thin for my tastes. I'd use the next size up which would make for a stronger joint.  If you were using traditional M&T , your tenon would be much thicker.  I can't say your results would measure differently.  It's just how I would construct that joint.

Even when your domino joint broke, it still had some mechanical properties holding it together and stands a reasonable chance of remaining intact.  Once those screws pop , you're really left with an unglued butt joint as not much of the screws bite into the wood anyway.

For me, pocket screws are only advantageous when I'm putting two pieces together without clamps or something that needs to be done fast and won't be subject to much stress.  Not the traditional uses for sure.

 

[jaguar36]

The domino you used is a bit thin for my tastes. I'd use the next size up which would make for a stronger joint.  If you were using traditional M&T , your tenon would be much thicker.  I can't saw your results would measure differently.  It's just how I would construct that joint.

Since the Domino didn't break a thicker one wouldn't make much difference as it wouldn't have substantially larger glue surface.  A longer one certainly would have though, and I'm going to give that a shot.

 

[ChuckM]

FW did a joinery test in 2008, including the dominoes:http://www.finewoodworking.com/2009/02/25/joint-strength-test

Part of the results:

DOWELMAX 759 lb.
¼ -IN. M&T 717 lb.
POCKET SCREW 698 lb.
DOMINO 597 lb.
BISCUIT 545 lb.

 

[HarveyWildes]

I use Festool Dominos for applications that don't require maximum strength - alignment, etc.  For joints where I want the most strength, recently for bench leg mortise and tenons, I use homemade Dominos that fit the maximum width that the machine will cut, and the maximum depth, minus 1-2 mm for so for glue squeeze.  On my bench project, this nearly doubled the glue surface area of each joint.  Also, I had the room, so I doubled them up.  Even at that, I'm sure they aren't as strong as through mortise and tenon joints, so I still resort to those occasionally.  I'm assuming that the joint glue surface area is one of the main contributors to the strength of a joint.

I don't have enough history with Dominos yet to know what the practical strength limits are.  We'll see if my bench collapses, I guess.

 

[ChuckM]

None of my DJ builds have failed, including the nook table shown here.

The acid-test, to me, is its use in chair-making. I will be making a pair of chairs to match the nook table in 2018 (too many projects, too little time!)

P.S. For the nook table, I deepened the mortises cut by my DF500 and used the longer Dominoes intended for the 700.

 

[antss]

Like I said - your test may not be different but a larger tenon would make for a stronger joint . 

You've chose to focus on the glue surface of the butted surfaces.  That in and of itself is not what makes for a strong joint.  I'll stack up  big ol honkin tenon in a tight mortise with two pins and no glue against any glued joint you want.

Chuck _ I agree a chair is a good bellwether for joints.    Nice inlay on that table BTW. 

 

[HarveyWildes]

...
You've chose to focus on the glue surface of the butted surfaces.  That in and of itself is not what makes for a strong joint.  I'll stack up  big ol honkin tenon in a tight mortise with two pins and no glue against any glued joint you want.
...

In my case, I was referring to the glue surface of the larger homemade dominos, not the butted surfaces.  The larger homemade dominos fit as tightly as the Festool ones, and the comparison I was trying to make wasn't between mortise and tenon and dominoes - it was suggesting ways to make a sturdier joint with the Domino tool than you can get with the Festool OTS dominos.  That said, I do agree that mortise and tenons are going to beat Dominos for strength if both are well executed.

 

[Steven Owen]

None of these tests are measuring the larger dominos from the DF 700.  DowelMax would have a hard time making a video to prove dowels are stronger than a group of 14 mm wide and 70 mm deep domino.

I can’t stand watching the DowelMax videos.  They’re condescending and always focused on bashing other jointing methods without any real understanding of how the equipment was meant to be used.   

After watching the Wood Whisperer it’s hard to watch the DowelMax videos.  You feel you might have to duck down fast to avoid the crazy angry old guy with a dowel fetish who will start throwing dowels at your head if you say anything about domino being better.

 

[smorgasbord]

Yet another (flawed) test recently posted:

Domino wins, but wood is "old growth douglas fir," which he claims isn't as strong as hardwood.

No failure analysis - which part of the joint gave way first?

This video doesn't include a Domino, but does confirm an earlier FWW article (seehttps://www.festoolownersgroup.com/festool-tools-accessories/domino-joint-strength/ for FOG discussion) that the lap joint is the strongest. Which suggests that the lap joint's large glue area that is clamped with pressure is the key element.

This second video also shows that with a long enough tenon/dowel (and I assume Domino), the strength of the joint can be increased such that the wood itself fails along the grain away from the joint. So, if you can run your domino 25mm deep (or deeper on the XF 700), this test says you should.

 

[Cheese]

Domino wins, but wood is "old growth douglas fir," which he claims isn't as strong as hardwood.

I don't know about that... [smile]

I've never had nails bend in maple or oak but they sure did bend in old Doug fir.

 

[Birdhunter]

Odd, but in over 40+ years of woodworking, I've never built anything that required cantileverd strength.

 

[smorgasbord]

I don't know about that... [smile]

I've never had nails bend in maple or oak but they sure did bend in old Doug fir.

There's a difference between "old growth" Doug fir and "old Doug fir."  Douglas fir gets harder with age. Which is part of why it makes a good building material - not so bad to build with, but gets stronger years later. Which makes remodeling somewhat harder.

 

[semenza]

        I am not sure what the point is of many of these strength tests? For the most part they simply end up showing that almost all of the methods are more than strong enough for furniture , built-ins, cabinets, and most other things.

      In this most recent one 100+ pounds applied on about an 8" long lever. Yeah, those are all pretty much going to work and hold up in any realistic build.

  Once you get to strong enough it really becomes all about the machining and assembly method. I mean that in relation to the build procedure efficiency and preference.

      I think little had to do with the type of wood because these were all breaking / pulling out at the glue joint. Except the pocket hole which cracked where the screw goes through, which is entirely predictable.

Seth

 

[ChuckM]

If you ask me, the furniture piece that really needs the strongest joinery is a chair because it is subject to severe racking. Cabinets/bookcases and carcases (back), tables (aprons/stretchers), and most other common pieces all have other structural elements supporting the joints, and never are subject to the same degree of stress as a chair is.

Maybe a domino joint would fail after a century, I don't know. But I do know if I made a tenon joinery mistake, the only way to undo it...was to start over with new components (unless the glue I happened to use was Old Brown Glue)! 

 

[smorgasbord]

I can’t stand watching the DowelMax videos.  They’re condescending and always focused on bashing other jointing methods without any real understanding of how the equipment was meant to be used. 

First, I agree with the person that posted about the OP test that 30mm dominos just aren't long enough.

As for DowelMax, yeah, pretty biased:
1) For these cantilever type tests, even if the width of the rail is kept the same, the width span of the dominos needs to be matched to the width span of the dowels. Here's a screen grab:

[attachimg=1]

You can see that the outermost dowels are very close to the edges of the rail, giving them the largest span. If the two dominos had been moved to have the same outside span distance (overall tenon width), I bet the results would have been a lot closer.

2) One of the advantages of Dominos is the adjustment you have available while gluing. Even on the Tight setting, there's a small bit of alignment adjustment possible (more if you trim the dominos or cut one of the mortises on a looser setting). With dowels, there's no alignment adjustment possibilities at all.

3) The Domino is way faster to setup, especially on stock that isn't about 19mm thick. With the DowelMax, you're looking for spacers to insert for thicker stock, or looking for spacers and screws for thinner stock:
[attachimg=2]
And, even then you have to manually set a stop collar on the drill bit to get the right depth.

4) The DowelMax is pretty much limited to 90 and 45 degree joints. There is a fixed 45 degree attachment, not an angle adjustable fence. And since you're using spacers instead of a height adjustable fence, setup is way longer:[attachimg=3]

5) There's no dust collection on the DowelMax. For deep mortises, multiple drill passes are needed to pull up the bit so that dust mostly clears.

 

[Svar]

5) There's no dust collection on the DowelMax. For deep mortises, multiple drill passes are needed to pull up the bit so that dust mostly clears.

Two passes at most. I actually like that, drill does not produce airborne dust. I wish they designed a window (similar to pocket hole jigs) for the chips to clear. Domino, on the other hand, CAN NOT be operated without a vac.
I have and use both, and both are excellent. Each has its own advantages.

 

[smorgasbord]

I have and use both, and both are excellent. Each has its own advantages.

I can certainly believe that. Which did you buy first, and today how do you decide which to use?