Strength of Domino... Test Results

I haven't seen the article yet either.  But Dan's right...Wood Magazine must think highly of the Domino given their comments about it on their online video.

(http://www.woodmagazine.com/wood/story.jhtml?storyid=/templatedata/wood/story/data/1178129509968.xml&catref=cat5610002)

The thing that has people worked up here is that Wood provided specific numbers about the pressure needed to cause failure in each of the joint types.  Since they only did one test of each joint, those numbers aren't really reliable.  You'd need to test each joint several times, with consistent methods of construction, to produce accurate numbers.

But, of course, I sure don't want to see statistical tests when I open a copy of Wood!

 
snip

> That being the case, are we talking about the differences of cars capable of going 175 or 200 mph when we would never need to exceed say, 75 mph?

> PaulD

The dowel joint in question was actually two dowels.
On the shear test, (I think of it more as a torque test)
The dowels appear to have been placed about 1/4-3/8"
in from both ends of the part and maybe 3/4" apart.
It was the wood BETWEEN the dowels that failed, pulled
out of the end grain part.

The DOMINO was the authors choice because a) all
the joinery tools evaluated would do a more than
adequate job of joining two pieces of wood
at 90 degrees.  But it was the speed that was
the author's deciding factor - the DOMINO being
almost as quick and convenient as the biscuit
joiner and 4 to 10 times FASTER than any of
the other methods evaluated.

And THAT is what makes the DOMINO head
and shoulders above the rest - even with
it's Stunner price tag ('til you compare
prices with the Leigh FMT or MultiRouter.

charlie b
 
Dave,
Gary is a member here in the forum.  He's only posted two messages so far in the forum, but he sent me an e-mail about the Domino strength test, and pointed out WOOD's November 2006 test.

Maybe he'll post here...

Matthew
 
  OK, I looked at the torture test article and they did the "shear" test at 3" from the vertical mortise. The way these joints are breaking seems to be more dependent on torque applied about a point below the mortise. So if we change the numbers to ft-lbs of torque we get: dowel joint    250ft lbs
                                                                      biscuit joint    62 ft lbs
                                                                      pocket holes  93 ft lbs
                                                                      Domino          116 ft lbs
In the real world this would translate to a chair joint breaking if you rocked it onto the back legs with this weight person on the edge of the seat(chair seat 14" with 1" overhang)(no braces under the chair).

These numbers looked kind of low so I made some joints with Titebond 3 took them to the basement and did a "scientific" study of my own. ;)

My test was even worse than their test(more like a table leg and apron). I made "L" shaped sections 1' long with the joint at the top (the T shaped sections are stronger) and hung weights off the end of the upside down "L"

I used 3" x 3/4" wide poplar stock since that is the width I had on hand. I put 2 Dominos(8mm) in the end 3/4" from the edge. It split the mortise at 101 ft lbs. The wood failed(split) behind the mortise.

I tried one Domino. That failed at about 200 ft lbs.

I switched to 6mm Dominos 3/4" in from the edge. I was not able to split the joint( I hung off the end standing on a 20 lb weight (200 ft lbs total) ;D). I will try to bust this again later with a longer lever arm. But it is strong enough for me.

So lesson learned, bigger is not always better. The 1/3 rule should be applied to mortise thickness(the weak part of the joint) (at least in poplar).

I encourage people to bust some stuff and post their findings so we can have some design parameters.

 
Mike_Chrest said:
   ...I made some joints with Titebond 3 took them to the basement and did a "scientific" study of my own. ;)
...
I used 3" x 3/4" wide poplar stock since that is the width I had on hand. I put 2 Dominos(8mm) in the end 3/4" from the edge. It split the mortise at 101 ft lbs. The wood failed(split) behind the mortise.

I tried one Domino. That failed at about 200 ft lbs.

I switched to 6mm Dominos 3/4" in from the edge. I was not able to split the joint...

So lesson learned, bigger is not always better. The 1/3 rule should be applied to mortise thickness(the weak part of the joint) (at least in poplar).
Click to expand...

This is very interesting and a bit surprising. Thanks for sharing Mike.
 
I have gone over the article in question comparing
a dowel joint (actually a TWO dowel joint), the
Beadlok, DOMINO and biscuit joint.

The "pull apart" test apparently was done
as follows:

Take a "T" and fix the "short leg"
Apply weights / downward force off the "long
leg".

For the "shear test" turn the "T" on its side
fix the ends of the "short leg" and apply weights
/ downward force on the horizontal "long
leg" at a fixed distance from the joint inter-
face.

The resulting values given were for the values
at "joint failure" - in most instances when the
surrounding wood tore apart.  And THAT is
measuring a) the strength of the wood, not
the strength of the joining method.

The German Festool site shows the results
of a better test for "shear"/torque
- WITHOUT ANY GLUE.    Here's the
"translated into english" version of their
DOMINO stuff's table of content.
http://translate.google.com/translate?hl=en&sl=de&u=http://www.festool.de/artikel/artikel_weiterleiten.cfm%3Fid%3D5145&sa=X&oi=translate&resnum=8&ct=result&prev=/search%3Fq%3DFestool%2BDOMINO%26start%3D70%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DN%26as_qdr%3

click on "Overview" to get to the illustration
of their testing method.  Basically they
used an "L" on its side - the "short leg"
vertical and fixed, the long leg horizontal.
They apply 145 Kg (about 319 pounds) of
force to the horizontal member, beginning
at the joint interface and moving away from
it until the joint "fails". 

Their results show that the dowel joint failed
at 2.2mm, the biscuit at 2.1mm and the
DOMINO at 14+ mm.  Translated into Foot
-Pounds - the dowel came apart at 2.3 ft-lbs,
the biscuit at 2.2 ft-lbs and the DOMINO at
14.65 ft-lbs - all without any glue.

The danger with "testing" is knowing what
you want to test and THEN designing a testing
procedure that eliminates all the other variables.
In the test that showed a dual dowel joint
"was stronger" than a loose tenon joint - they
didn't eliminate the "glue" variable or the
"strength of the test wood" variable.

Woodworkers are clever folks.  But in this
article's case, they should have consulted
and engineer when designing their test.
Bad "science" is worse than no "science" at
all.  I'll leave "Intelligent Design" for another
forum.

charlie b
 
Charlie,
  I think you should look at the Festool test again. It is the same one I tried. From what I found in the brochure they did glue the joints. Also I believe they were measuring the deflection of the horizontal member before failure.
  I believe they increased the weight until failure but they didn't say what distance the force was applied at so we can't translate their numbers into torque. I believe they stopped the test at 145kg (319 lbs)
  It makes no sense to test a joint like this without glue. Think about it (a biscuit joint would just hinge open). If all the joints used the same type of glue and were clamped the same time the test should be valid.

"Woodworkers are clever folks.  But in this
article's case, they should have consulted
and engineer when designing their test."

I saw a similar test in Fine Woodworking which did use an engineer and he determined that you could hang a pickup truck off a mortise & tennon joint :o. If you look at the way he stresses the joint you can see he built a trestle and tried to break it by pushing down on the apex. This test is not valid unless you have a perfectly frictionless base.

So here is a case of "good science" with no regard of how the joint is actually used in furniture( it's a good test for sawhorses ;D).

Mike

PS: I'll bet there are quite a few engineers on this forum ;)

 
 
I finally got a chance to head over to Barnes & Noble last night and read Wood magazine's strength test. 

The article did leave me confused about a few points, especially how they arrived at their strength numbers (displayed in cute graphs).  Reading the text, it seemed that there was not as much consistency in the methods for testing each joint as I would have hoped for.

I was puzzled by the fact that instead of rating biscuits generally, they rated the Porter+Cable biscuit joiner.  In my experience, all biscuits are essentially the same, so why create confusion by making it sound as if your ratings are for a particular brand of biscuit joiner?  This may leave readers wondering if other models produce better joints.  This is beyond the scope of our Festool-related discussion, but it does open questions about the design and thinking behind this review.

In one statistic, the review cites "cost per joint" for each method.  I'm sure it was unintentional, but in my opinion this at best a useless stat, and at worst misleading.  For example, the review did not account for the number of unusable biscuits one is likely to find in a typical jar of biscuits.  Even so, comparing the cost per joint makes it seem that you can determine the cost for getting an equivalent result using different methods.

In the end, the reviewer gave the Domino the best overall marks: A or A- in every category.  And in the text of the review, the reviewer says that the Domino is the tool he would want to own.

Although the details of the tests would lead you to think that the Domino would rank perhaps second or even third overall, in the summary the reviewer ranks the Domino highest (A) in strength.  This is a good result for the Domino, but it is somewhat confusing, as it does not jive with the text or the charts in the review.

This strength test opens more questions than it answers for me.

I'd like to put together a letter to send to Wood, asking for clarity.

Matthew
 
Matthew,
  I emailed Bob Wilson the author of the first Torture Test article and asked if he would test a sample with two 6mm Dominos in one joint. He didn't sound too enthusiastic :-\. He said they already had lots of samples to try and not much $$ to spend. He said he would "keep in mind" the Domino thickness issue for future testing.
  I think your right that a letter from the group might carry more weight.
Mike
 
I think we're worrying about this too much.  It's apparent that the strength numbers the magazine achieved with the all machines except the biscuits are plenty strong and probably overkill.  They rated the Domino the best of the lot.  What more can they do? 

PaulD
 
Mike_Chrest said:
Matthew,
  I emailed Bob Wilson the author of the first Torture Test article and asked if he would test a sample with two 6mm Dominos in one joint. He didn't sound too enthusiastic :-\. He said they already had lots of samples to try and not much $$ to spend. He said he would "keep in mind" the Domino thickness issue for future testing.
  I think your right that a letter from the group might carry more weight.
Mike
Click to expand...

Was he unenthusiastic because you questioned his testing methods, or was it because he didn't feel a new test was necessary, or something else?  By the way, how much money does it cost to run this kind of test?  I could essentially do something like this in my little one-man shop.

bassman00 said:
I think we're worrying about this too much.  It's apparent that the strength numbers the magazine achieved with the all machines except the biscuits are plenty strong and probably overkill.  They rated the Domino the best of the lot.  What more can they do? 
PaulD
Click to expand...

You're right, they did rate the Domino highest, which is fine for me, and for others.  But I'm thinking from the perspective of the readers who come in not knowing much about the Domino or Dowelmax or biscuits, or loose-tenon joinery in general.  In other words, I'm thinking from the perspective of the way I once was when I first learned about these subjects.  I know that article would have left me confused.  At the same time, the article would have left me with the impression that the Domino is a great tool.  So maybe you're right.  It's just in my nature to respond to these kinds of things!

Matthew
 
Matthew,

I share your interest in accuracy and fairness, and it bothers me that a test was done that left unanswered at least as many questions as it answered.  Further, the article's limited critical thinking, testing, and analysis lowered my opinion of the the magazine.  That said...

A very POSITIVE aspect of the article is that it caused US to question critical aspects of joints, specifically around the size, number, and placement of tenons.  It seems like multiple, smaller loose tenons are stronger than a single larger loose tenon. 

Prior to the Domino, I wonder if people ever addressed these questions.  I suspect not.  This flies in the face of the notion of "bigger is better".  And, using traditional methods, creating joints with multiple, accurately-placed loose tenons is not that easy.  So it would be a hassle to test.

Because the Domino can drill out multiple mortises quickly and accurately, and because the tenons (dominos) are manufactured, a major limitation of traditional M&T methods - the effort to cut the mortises and make the tenons - is reduced or eliminated.  Now it's relatively easy to install multiple loose tenons. 

The problem is that we are still experimenting with this tool.  It looks like many people are using it with traditional methods - stuff a single big fat tenon in a big fat mortise.  Although experienced Domino users like Tezzer, Rocker, Jerry Work, Risk Christopherson, and Per Swenson have done some great work and expanded our frontiers, I suspect that the techniques and "rules" for using Dominos will continue to grow and new techniques will continue to evolve.    The best combo of size, number, and placement for a given application is still evolving. 

So, while I agree that the article's test had some major faults, it raised a lot of questions that need to be answered.  IMO, that is far more important than anything else.

Regards,

Dan.

p.s., I can now say "We" because I received my Domino last night!    ;D
 
Matthew,

Was he unenthusiastic because you questioned his testing methods

  No, I told him the article was interesting and informative(which is true)(it might not be good enough for grad school but you can pull trends from small samples.

or was it because he didn't feel a new test was necessary, or something else

I think they are going to do another article. I can forward you the email if you like.

I could essentially do something like this in my little one-man shop.

This is what I was suggesting when I posted my first response. The FOG could make sample joints in our shops break them and publish the results. The more samples we collect the more accurate our findings. I can post pictures of the setup if anyone is interested.

Dan

Because the Domino can drill out multiple mortises quickly and accurately, and because the tenons (dominos) are manufactured, a major limitation of traditional M&T methods - the effort to cut the mortises and make the tenons - is reduced or eliminated.  Now it's relatively easy to install multiple loose tenons.

Very well put. My customers wouldn't pay for mortise and tennon joints without the Domino. Set up and cutting is extremely fast. I have used 1000 Dominos this month. You will love yours ;D

Mike
 
Hey Guys,
    I understand the importance of being reassured that you have a strong joint, but how many of us are actually going to exert these kind of forces on our furniture.  The most we have to probably worry about, is one of our lovely guest, that loves to eat, resting their 250 plus pounds on the furniture. If you really want to be certain, then make a prototype of your piece and put it through your own test, like the guys in the zigzag chair photo did.  Prepare your own results and share them with others that way you will know how strong you domino joints are for sure.  I don't plan on parting with mine any time soon!
 
Rescue U,
You make a good point about joint strength.  A lot of the methods we discuss here are stronger than we need for most occasions, and are not likely to experience the stress of the tests.  But this opens a wider question, I think, about modern woodworking as new tools are available to us.  Should we or should we not try to go for the very strongest joint possible?

But still, if someone is going to assess joint strength, the results should be accurate and as clear as possible.

And if strength is not an issue, we should then look at other factors, which the Wood test did, such as ease of assembly, consistency of the joint, attractiveness, and versatility.

I would love to see members run their own strength tests and post them here in the forum.  I'm positive people here would come up with new ways to test the joints.  We have a lot of great minds here.

Matthew
 
Speaking of user run strength tests, I think Rocker's picture of the three gentlemen standing on his Z Chair is telling enough.  >500lbs on a joint that looks like it should want to separate easily is good enough for me.  The weights listed in the article are for one joint only.  Since most furniture pieces are built where each joint sort of compliments each other, those weights will be double, tripled, etc.  I don't plan on parking small cars on the stuff I build so strength will be fine.  Plus, I'm sure if the strength wasn't good enough, we would've been hearing about it.  Then again, if the joints created by the Domino weren't strong, I doubt Festool would release it.

Dan - I don't remember where I heard it, I think it was when I was researching the FMT, but I heard from reputable sources that multiple smaller M&T (be it loose or integral) are better than one large one.  Makes sense in that there's less stress on the mortise.  Wish I knew that when I built my daughter's bed as I used some large tenons for that.  Fortunately, I kept it at 1/3 the width of the legs and all components are overbuilt since I plan on lofting it when she gets older and needs more room in her room.

PaulD
 
bassman00 said:
Speaking of user run strength tests, I think Rocker's picture of the three gentlemen standing on his Z Chair is telling enough.  >500lbs on a joint that looks like it should want to separate easily is good enough for me. 
PaulD
Click to expand...

Don't assume the Z joint is a simple application of Dominoes.
It is actually quite sophisticated.
 
Bassman,
  Rocker's picture of the three gentlemen standing on his Z Chair is telling enough.  >500lbs on a joint that looks like it should want to separate easily is good enough for me. 

Rocker's joint puts the Domino in tension (its strongest application). He has it embeded in some wicked hard strong Aussie "wood" (jarrah). The tennon is made of the same wood. I think he pinned the tennon as well. I applaud his joint design.

The point that keeps bugging me is you can't lump all mortice & tennon joints together. Here is a joint that I hoped would be very strong. It broke with 100 lbs on it. If this was a table leg 2ft long, you would only need a sideways force of 50 lbs to break it.

Note, the wood broke, not the joint. But the joint weakened the wood. So we have to study joint design.

 
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