Domino joint test in FWW...

[marrt]

Anyone see the FWW "Joinery Test" article?  I thought someone would have mentioned the article on FOG, but my search didn't find anything.  Anyway, the Domino joint didn't do as well as I would have thought. Here's a link to the article if you are a FWW subscriber:  Joinery Test

 

[nickao]

Looks like the old ways are still the best ways.

 

[Tom Ryan]

I don't have the article in front of me, but as I remember, the domino was smaller than other loose tenon things tested -- so it didn't seem like a fair test to me.

Tom in SE Pennsylvania

 

[nickao]

It does not matter. None of the joints broke at the joint connection point, but the wood broke out.

That tells me the Domino is just as good as anything else in that category joint. Also I do not think a 50lb force is much of a difference when you are near 500lbs anyway in terms of a piece you will make.

Any of the forces in the article are never going to be applied to what you make with a Domino unless you are trying to bust the thing apart on purpose.

I'd keep the Domino if it works for you and not give it another thought.

 

[Jesus Aleman]

I agree.  Many of the tests (whether standard or not) are conducted at forces higher than what experienced under normal use.  I work in engineering consulting  and many times we pressure test pipe joints for water service at 150 to 250 psi even when the pipe in service will see only 15 to 30 psi.  At the test pressures there is a significant difference between steel and plastic pipes, at the service pressure there is little difference (pressure wise). 

I have torn apart plywood/pressboard furniture with failure at the material not from the dowel or pocket screw.  However, I have seen several times where the material fails around the dowel because the material that surrounds the dowel was too thin.  Think about it.  For a given material thickness, you could insert a domino of equal glue surface area that a dowel, but because of the rectangular shape of the domino you would have more material around the mortise. 

I would look at the domino as a tool (not THE TOOL) that provides great flexibility (location) and production speed for a joint that is reasonably strong (not the strongest though).

BTW, the above are only my impressions and opinions at a hobbyist.  No hard science behind it.

Cheers,

JGA.

 

[Groggy]

The test results are not consistent with results of tests done previously by the same magazine (author was Gray last time I think). Previous tests had M&T as the clear winner so I am not sure which to believe, if any.

The only comfort I can draw is that the modern glues, if properly applied, make virtually any joint strong enough to use.

 

[extiger]

If you consider the direction of the forces based on the test device (shown in the photos), it seems the test is for torque. Real life forces, however can come in many directions. A strictly sheer force one finds at most joints would favor a mortise & tenon or a domino. A chair usually exerts a straight sheer force, except when the occupant rocks the chair. Same for any frame and panel or stile/rail configuration.

For that case, the FWW test would be quite appropriate. Also important are the stresses over time, in which case the dowels wouldn't do so well. Wood movement simply fractures the glue joint, and we've all seen old TV cabinets ( I mean from the 60's) in which the sides separate exposing dowels coated with dry, powdery glue coating the dowels.

If FWW rated biscuits as stronger than Dominos, they aren't discussing the cabinet and furniture joints I prefer to make.

Gary Curtis

 

[nickao]

Well the glue in the 60's is nothing like it is now so I think that comparison may not be quite as valid now.

The test results were close for Biscuits and Domino's, close enough to call them the same strength based on the testing  numbers. Every piece of wood, the biscuit and domino vary in strength somewhat. Different glues are used too and I just think 50lb difference is negligible.

I do not think a domino is ever close the the strength of a Mortise and Tenon, under any circumstance, using any woods, under any conditions, IMHO.

 

[fshanno]

Based on the performance of the single domino I'm more pleased than ever that I dropped the $700.  It's still my coolest tool by far.

 

[Ken Milhinch]

Looks like the old ways are still the best ways.

I have to agree with that.

 

[Jim Becker]

It does not matter. None of the joints broke at the joint connection point, but the wood broke out.

That's my observation, too. For those joints that used some form of "tenon" (including dowels, Domino, etc.) the failures tended to be in the material, itself, and just beyond the tenon. What that tells me is that joints expected to have to resist higher loads should have longer, beefier tenons. The results for the bridle joints make sense since these, in a strong way, mimic a very long tenon with a large glue surface.  No real rocket science here!

 

[marrt]

I wish they had used plywood for the test.  I imagine differences in the individual pieces of wood could make a huge difference.

 

[EJB]

I have not read the test article yet.....

but.....

I agree that they should have used plywood as a control and another wood. Also, the test would need at least 20-30 replicate tests for each case and joinery method for any kind of understanding of the mean and the range of forces at which the joints broke....This would take an incredible amount of time....but if they want to get proper results  that's what needs to be done..  Perhaps they did do many replicate tests...  If the replicates are done one can see where the statistical differences are..if any..... 

Ed

 

[Notorious T.O.D.]

...and I bet I can make a good biscuit joint that is way stronger than a poorly executed Mortise and Tenon too...

...Did I mention that I hate biscuits...

Best,
Todd

 

[slb]

I agree with several previous posts that these tests aren't very realistic.  I think in the real world the applied loads are nowhere as big as in these tests (unless, I suppose, you have 900 lb people sitting in your chairs!).  So, the tests aren't looking at the reasons or ways real joints fail. 

The failures I've seen are from older glues that broke down (maybe fungus or bacteria eating them?), fractured because they are very brittle, or gradually came apart after years of seasonal expansion and contraction of the wood.  The eventual failure under load was because these effects or others like them had already weakened the joint.  I've never seen a brand-new joint fail unless it was very badly fitted, glue-starved, or wildly inadequate for where it was used.  I'm not worried about the strength of domino joints, and I like the speed and precise alignment they provide.

That said, in the unreal world of the tests, it looks to me like the dominant factor is the amount of face-to-face grain area in the joint.  With enough f-t-f area, the tester had to fracture the tenon across its grain because the glue is stronger than the wood.  Second is the amount of end-to-face grain area (which flies in the face of all the classic advice that end grain provides no strength in a glue joint!).  Notice that in most of the failures the stile (mortise) piece failed by splitting along its grain parallel to the joint.  Dominos and bisquits provide similar amounts of end-to-face area, and they tested (relatively) close in strength.  It would be interesting to see if a joint using several 5mm dominos would test stronger than the one they used, with a single 10mm domino.

 

[nickao]

The tests may not be realistic, but I agree with the order of strength results.

I do not think real world situations are going to make say a domino stronger that an M & T.

I think the testing has value as far as showing you the RELATIVE strengths of the joints.

 

[Neill]

Nick,

I would guess that these tests only consider "perfect joint vs. perfect joint".  An M&T joint is hard to get perfect, that is 1/3 mortise, 1/3 tenon and 1/3 mortise centered with no gaps.  A domino joint is much easier to get perfect, or close to it.

So in order to get the perfect M&T joint you need time, the right tools (such as a hollow chisel mortiser and a table saw with a tenoning jig) and a certain level of expertise.  The domino is quicker to setup and use even for a novice.  You cut the mortise and insert the loose tenon that best suits your needs.

Neill

 

[nickao]

I think it is a matter of what you do,.  I know plenty of guys that zip through M&T so fast you can't blink. And an M&T does not need be near perfect to be strong against breakage at all. Ever try taking the joint apart apart, good luck

The Domino is nice, but there is no way I can ever compare the quality and beauty of the joints. The M&T is my joint of preference for fine furniture and almost anything if I have the time.

Simply, the Domino is great for what it is, but I do not compare it to a traditional M&T. If I did I would be kidding myself.

Many said they wanted the test to use plywood. I do not waste time on an M&T on plywood. The uses of the Domino are just different more in line with a biscuit or dowel system.

I'll say it again all the joints they tested are fine for woodworking, especially with the newer adhesives. So pick your favorite and run with it. There are may things that the Domino can do that can not be done with and M & T and shouldn't be done, in those instances the Domino is sweet!

 

[Dave Ronyak]

IThat said, in the unreal world of the tests, it looks to me like the dominant factor is the amount of face-to-face grain area in the joint.  With enough f-t-f area, the tester had to fracture the tenon across its grain because the glue is stronger than the wood.  Second is the amount of end-to-face grain area (which flies in the face of all the classic advice that end grain provides no strength in a glue joint!).  Notice that in most of the failures the stile (mortise) piece failed by splitting along its grain parallel to the joint.  Dominos and bisquits provide similar amounts of end-to-face area, and they tested (relatively) close in strength.  It would be interesting to see if a joint using several 5mm dominos would test stronger than the one they used, with a single 10mm domino.

I would bet on the plurality of 5mm Domino tenons over the single 10mm Domino tenon.  Distributing the same total load over greater areas of both the glue interfaces and throughout the wooden members being joined spreads that load over a greater number of wood fibers and should provide greater load carrying capacity.  Failure in any material occurs when the localized load ("stress" is the term engineers often use) exceeds the inherent load capacity of the material itself.  For another example, consider why the cable wires in a suspension bridge are individually tenioned.  If each is carrying its intended share of the load, all is well.  But if some are overly stressed, they will break, then the remainder become over stressed and they break, too, resulting in total failure of the cable.  Another example exists in truss fastners, whether joining pieces of lumber or pieces of steel.  In each truss fastener (or gusset as some call them), there are a plurality of actual interconnection point to spread the total load out across the components being joined.  I think the old rule that the integral wood tenon be 1/3 the thickness of the stock is a simple, practical and effective compromise that works well, but with thicker workpieces, multiple mortices and tenons can deliver better (stronger) joints.

I wonder what results would have been obtained in testing various finger joints such as those made with specialized router and shaper bits.  If properly fitted and glued these should be as strong as the boards themselves.

Dave R.

 

[butzla]

I was surprised to see pocket screw joinery scoring much higher than biscuits and dominoes.