Festool Owners Group

FESTOOL DISCUSSIONS => Festool Tools & Accessories => Topic started by: MCASE on June 06, 2009, 10:55 PM

Title: domino joint strength
Post by: MCASE on June 06, 2009, 10:55 PM
Fine Woodworking  published the results of joint strength tests in their January 2009 issue (#203).  They tested  eighteen joints:  half laps, bridle, mortise and tenon, floating tenon,  miter, splined miters, dowel max,  bead lock, domino, biscuits etc.   They attached a rail to a stile with various joints and tested them in a lab under controlled conditions  for lever strength. The range of the results  ran from  1660 pounds of breaking strength for the half lap  joints to a meager 200 pounds for the stub tenon.   Traditional mortise and tenon rated near the top with a breaking strength of 1444 pounds followed very closely by floating tenon at 1396 pounds    The bad news is that the domino placed #14 out of 18 at a lowly 597 pounds, just above biscuits at 545 pounds.
 I replicated these tests for half lap,  mortise and tenon,  floating tenon, biscuit, and of course domino.   I used  used 1x2 1/2"  stock and a simple vise and my arm.  I performed the tests twice for each joint, once in red oak and once  in white pine.  I used Tightbond's original glue and allowed each joint to dry for three days.  Obviously I can't give a psi specification for breaking strengths, but I can tell you that my results paralleled those published. The half lap was incredibly strong , The mortise and tenon and floating tenon were also very very strong.  The biscuit sheared off  easily, but this was no surprise.  Sadly the domino (#8 50 floating)  joint broke with sickening ease.  The domino (#8 50 tight)  joint was a bit tougher, but was not very impressive.  Using two dominos if you can work them in substantially improved the joint, but fell well short of a mortise and tenon or floating tenon.   The shortcomings of the domino surprised and saddened me.  The questions for  Festool Domino owners is why so weak and what do?
      In my opinion, the weakness results from the relatively slim glue surface of the domino.  This shortcoming has in my opinion been exacerbated by
the impressed pattern on the Festool  dominos.  Initially, I assumed that the beech domino was meant to swell like a biscuit and the impressed pattern  on the domino would swell up and disappear.  But this was not the case.   On the joints I tested these impressed patterns did not swell out from immersion in  water based glue, but remained impressed. I do not know what Festool hoped to achieve by adding these impressions,  But they result in a further reduction of glue surface.   They  reduce the wood to wood contact by creating a series of gaps along the whole glue surface thus weakening the joint.  
    So what to do?  The answer is simple;  increase the glue surface by widening the glue surface and getting rid of the impressions.   You do this by using the domino joiner to make traditional floating tenon joints and making up wide smooth floating tenons.      I recently made up red oak floating tenons 1 3/4" wide x  2" long for the #6 domino bit.  Making up yards and yards of tenon stock is simplicity itself with a band saw and a planer.   I cut matching mortises in rails and stiles by lining up 2 Domino machine cuts to make a 2" mortise including the corners which provides a 1 3/4" flat surface.  I then glued up the joints using the smooth, wide, oak tenons.   The resulting joints  are enormously strong:  far, far stronger than using the dominos. This method was quick and easy and produced true chair-strength joints. So the Domino machine is a great addition to my shop, but without the dominos!
Title: Re: domino joint strength
Post by: Forrest Anderson on June 07, 2009, 06:00 AM
This shortcoming has in my opinion been exacerbated by
the impressed pattern on the Festool  dominos.  Initially, I assumed that the beech domino was meant to swell like a biscuit and the impressed pattern  on the domino would swell up and disappear.  But this was not the case.   On the joints I tested these impressed patterns did not swell out from immersion in  water based glue, but remained impressed. I do not know what Festool hoped to achieve by adding these impressions,  

As I understand it, the impressions/indentations on the faces of the Domino tenon are to "hold" some of the glue to stop it being wiped off the surface when you insert it into the mortice. Dominoes can be a very tight fit, so the action of inserting them into a hole tends to shear off a lot of the glue that you apply to the two faces. If the Dominos were smooth, then I suspect that too much glue would be sheared off and the joint would be starved of glue.

Dowels are are also fluted, partly to allow glue trapped at the bottom of the hole to escape upwards, preventing hydrolock, and partly so that all the glue doesn't get wiped off the dowel when you put it in the hole.

Forrest

Title: Re: domino joint strength
Post by: wooden on June 07, 2009, 09:09 AM
As I understand it, the impressions/indentations on the faces of the Domino tenon are to "hold" some of the glue to stop it being wiped off the surface when you insert it into the mortice. Dominoes can be a very tight fit, so the action of inserting them into a hole tends to shear off a lot of the glue that you apply to the two faces.

That idea is bunk.  If you apply glue to both the tenon and the mortise before assembly, you don't need to worry about the glue being wiped off.  Apply enough glue so that there is excess when you assemble the joint.  This ensures the matings surfaces have wet glue and not dry or partially dry glue.  Having wet glue is key to allowing the mating faces to bond.

Traditional mortise and tenon should be cut so the joint is 'tight.'  That is, once dry-fit, the joint should require active disassembly.  Simply pointing the tenon down (so gravity can pull the joint apart) should not allow the joint to slip or even worse, completely come apart.

I agree with the OP.  Make your own domino stock that is wider.  Mill the domino stock to match the middle width and widest mortises the domino will cut.  In general, glue joint strength correlates with the amount of surface area.  Dovetails are a different beast because they introduce mechancial interlocking in addition to glue surface area.
Title: Re: domino joint strength
Post by: Forrest Anderson on June 07, 2009, 01:18 PM
As I understand it, the impressions/indentations on the faces of the Domino tenon are to "hold" some of the glue to stop it being wiped off the surface when you insert it into the mortice. Dominoes can be a very tight fit, so the action of inserting them into a hole tends to shear off a lot of the glue that you apply to the two faces.
That idea is bunk. 

Interesting. So, what do you think the grooves and indentations are for, and do you think they are a good idea?

Forrest
Title: Re: domino joint strength
Post by: bionicus on June 07, 2009, 02:55 PM

Interesting. So, what do you think the grooves and indentations are for, and do you think they are a good idea?

Forrest

It's stated in the brochure that Domino tenons are "designed with expanding glue slots and side grooves," so I guess that answers that. I just think they went overboard with the size of the slots, especially if actual tenon expansion falls short of expected or designed expansion.

I'd be curious to see how 'blank' dominoes would fare in the same tests against production dominoes with stamped slots and Festool impressions.



Title: Re: domino joint strength
Post by: Tinker on June 07, 2009, 03:16 PM
What am I missing?
Are not Dominos floating tennons?
Tinker

Title: Re: domino joint strength
Post by: timbo on June 07, 2009, 05:10 PM
Could you clear up a point for me please? Did the domino itself snap?
Title: Re: domino joint strength
Post by: MCASE on June 07, 2009, 10:32 PM
Yes Tinker they are a form of floating tenon.   But they are narrow and textured with impressions.   They simply do not hold as well as wide,  smooth,  old fashion shop-made floating tenons.    The good news for all of us is that the domino machine is a great  mortise cutter.   It works with the simplicity and quickness of a biscuit machine and can easily be employed without modification to create old fashioned floating tenon joints.   It can do the job of creating truly strong joints in rail and stile, or chair leg, or whatever.   You can also use it with the very convenient dominos for all sorts of joinery that demand less strength.     There is no down side.  
Title: Re: domino joint strength
Post by: Terry Fogarty on June 07, 2009, 10:37 PM
As someone who has plunged literally thousands and thousands of  Domino mortises, I have also done my own strength testing and if you apply glue only to the tenons or just in the mortise, the join is weak. If you apply glue to both surfaces the joint strength is incredibly strong.
Title: Re: domino joint strength
Post by: MCASE on June 07, 2009, 10:49 PM
No Timbo,  the dominos themselves do not break.  Actually they have great shear strength.   With a single #8 domino the glue surface in the rail let go quite easily.  It surprised me that the parallel  grain glue joint in the rail let go before the cross grain.   A parallel grain glue surface should be as strong or stronger than the wood itself.  It was the strange nature of this failure that leads me to suspect the impressions might be interfering with  proper adhesion.
Title: Re: domino joint strength
Post by: MCASE on June 07, 2009, 11:11 PM
Tezzer,   Your quite right to point this out.  Your certainly not going to get a good joint by only gluing the tenon or only gluing the mortise.  I can't answer for the Fine woodworking group, but I assure you  I glued all mating surfaces on both tenon/dominos and the interior of the mortises.  I do this with all mortise and tenons,  having learned the hard way never to starve a glue joint.   If you did comparative tests and your  results differ from Fine woodworking's lab tests I'm not here to say your wrong.     But, I have to tell you I methodically went through a lot of joints in two different species of wood and found that my results with mortise and tenon, and old style floating tenon v. domino did confirm their findings.     If your achieving joints strengths that satisfy your needs then more power to you.
Title: Re: domino joint strength
Post by: wooden on June 08, 2009, 12:38 AM
As I understand it, the impressions/indentations on the faces of the Domino tenon are to "hold" some of the glue to stop it being wiped off the surface when you insert it into the mortice. Dominoes can be a very tight fit, so the action of inserting them into a hole tends to shear off a lot of the glue that you apply to the two faces.
That idea is bunk. 

Interesting. So, what do you think the grooves and indentations are for, and do you think they are a good idea?



A means to justify the very expensive price point?  This does not mean I don't purchase dominos.  I purchase many.

Also....I think dominos (and I know that biscuits were) are intended for joining cases made of engineered materials.  In this application, you would put many dominos into a single joint, making for a very strong joint.  In fact, I've dropped a dominoe'd plywood case and while I had to replace the case, the case did not fail at the joinery.  The plywood material dented where the case struck the floor....but the case stayed intact and even stayed square.
Title: Re: domino joint strength
Post by: Groggy on June 08, 2009, 07:26 AM
This is interesting. I read the FWW article but did not give it much credence because the results did not conform to a previous review done by the same magazine - which to believe?  ???

Anyway, I am thinking the weakened joint may be due to the domino being pressed to get the patterns in them. If the fibers are crushed then the outer layer which is in contact with the glue would be seriously weakened - would it not? This may explain the greater strength of a hand-made floating tenon. I wonder if there are similar disparities with dowels that have the glue 'flutes' pressed in them.

What do you reckon Tezzer?
Title: Re: domino joint strength
Post by: haconway on August 28, 2012, 12:41 PM
The research I have done lately suggests that for a mortise and tendon; the smoother the surfaces the better the bond of the glue.  A lose joint will never hold, also caked up residual glue inside the joint does nothing to hold the joint.  I believe also that if the mortise and tendon are the same species of wood, the bond will be better.   I think with beech style biscuits or tendons the theory is that it will swell some when saturated with glue, improving the joint.  This has been a proven method in chair building (Brian Boggs), using a tendon that is very dry and the matching mortise piece that has a higher moisture content,  the joint will naturally equalize very strong when the mortise shrinks down around the tendon that slightly expands (like the rung on a chair).    I think the posting response that said make your own dominoes is on the right track!   Also the one regarding spreading glue on both surfaces.   The glue absorbs into the wood better with this method.   Lastly if you are making furniture, you could also use the ancient tried and true and effective technique of "pegged draw boring" on one of the mortised sides after the glue has set on one side.  Our ancestors did this joint with out glue and it was very strong.   

I didn't see the article in Fine Woodworking so I went and looked it up.  Notice the #1 joint is the half lap.  Why is that?  Because it has matching broad surfaces for glue bonding.  The bond holds the wood together and not the mechanics of the joint.   

You cannot get around the ease and time saving of the domino over traditional methods, just a matter of doing it right.
Title: Re: domino joint strength
Post by: rjwz28 on August 28, 2012, 01:46 PM
The research I have done lately suggests that for a mortise and tendon; the smoother the surfaces the better the bond of the glue.  A lose joint will never hold, also caked up residual glue inside the joint does nothing to hold the joint.  I believe also that if the mortise and tendon are the same species of wood, the bond will be better.   I think with beech style biscuits or tendons the theory is that it will swell some when saturated with glue, improving the joint.  This has been a proven method in chair building (Brian Boggs), using a tendon that is very dry and the matching mortise piece that has a higher moisture content,  the joint will naturally equalize very strong when the mortise shrinks down around the tendon that slightly expands (like the rung on a chair).    I think the posting response that said make your own dominoes is on the right track!   Also the one regarding spreading glue on both surfaces.   The glue absorbs into the wood better with this method.   Lastly if you are making furniture, you could also use the ancient tried and true and effective technique of "pegged draw boring" on one of the mortised sides after the glue has set on one side.  Our ancestors did this joint with out glue and it was very strong.   

I didn't see the article in Fine Woodworking so I went and looked it up.  Notice the #1 joint is the half lap.  Why is that?  Because it has matching broad surfaces for glue bonding.  The bond holds the wood together and not the mechanics of the joint.   

You cannot get around the ease and time saving of the domino over traditional methods, just a matter of doing it right.

Just wondering, is the half lap joint stronger also because you are squeezing the joint together, glue on glue and not sliding one part over the next removing some glue?
Rob

Title: Re: domino joint strength
Post by: haconway on September 04, 2012, 08:00 PM
That might have something to do with it.  I also believe it is the mechanics involved once the wood is bonded together and where it creates the weakest link. 
Title: Re: domino joint strength
Post by: hhh on September 04, 2012, 09:31 PM
==> grooves and indentations

hydro-static pressure relief -- that is also the reason why you don't 'bottom-out' traditional m/t joints.  if you do enough draw-boring, then you will experience what hydro-static pressure does to a joint (you will occasionally blow-out the back of the stock).

dominos are fine for strength -- they are simply floating tenon joints with dissimilar species.  They should be no stronger/weaker then any other floating tenon joint.  if you are sloppy, then the fit will be loose -- the same as any floating tenon that is poorly fitted using traditional hand/machine techniques.  If the fit is loose, you would need a gap-filling adhesive or the joint will fail...

I've done over 2000 domino joints and have not had one fail yet.  i mostly use west systems epoxy because it is a natural gap filler.

As a side note, the FWW article that was mentioned in the OP has come under a lot of fire -- specifically because FWW did two articles on joint strength in the past few years that came to completely different results.  Most attribute the discrepancy to the limited sample size not permitting statistically significant results (T-test).
Title: Re: domino joint strength
Post by: Timtool on September 05, 2012, 06:30 AM
To be really honest the test would have needed to be between using a domino joint and a MT joint with a mortise and tenon of the same size as the domino.
They probably tested a perfectly proportioned and executed MT joint vs whatever domino came closest to it. The domino takes out the human error factor, the mortise and domino have the perfect fit each time. Making traditional MT joints is not as easy, with my benchtop mortiser the mortises used to be very rough on the inside and nowhere near as perfect in size and position, and machining tenons is also tricky to get right.
And nothing stops you from using the domino as a mortiser and make mortises of the size you want and make your own floating tenons, in that case i can't see why they would be less stronger than a regular tenon. Since i highly doubt the floating tenon will ever break in the mortise where it is aligned with the wood grain.
Title: Re: domino joint strength
Post by: jacko9 on September 05, 2012, 07:33 PM
I  find this to be an very interesting discussion.  I almost exclusively make hardwood furniture and have replaced my tablesaw mounted slot mortiser with the Domino 500 and the Domino 700 joiners.  It almost always makes sense to me to make my own floating tenons out of the same material I'm using.  I also can get better proportioned joints since I'm not limited on the joint width of the domino tenon.  I do however use the stock tenons when joining wide solid cabinet sides in multiple tenon joinery.  Good discussion and thanks for the experimental testing on joint strength.

Jack
Title: Re: domino joint strength
Post by: rjwz28 on September 06, 2012, 02:19 AM
A strength test that I would like to see would be to make two joints for the same size wood you would be using.  Say if you would butt a 3/4" thick x 3" high
 table skirt or rail to a 2" x 2" vertical leg, you would use the regular mortise and tenon for that particular joint (I'm not sure the correct size for this) and the other one you would use whatever Domino you would use for that same exact size material and then test the strength.  Then I think we could measure the joints fairly.  There's only so much size and number of Dominos that can fit in that configuration.

Rob
Title: Re: domino joint strength
Post by: itri on September 06, 2012, 05:00 AM
 Dominos may not be the strongest joints  but they are good enough for furniture making.They will last for years if we use them properly.This discussion,actually makes me think  about the difference in gluing strength between hide glue and modern glue.Hide glue may not be the strongest glue but it's good enough for furniture making and when it comes to repair ,it's easier .And it's easier too if we have to repair a floating tenon joint instead of a regular tenon joint,in my opinion.

Sometimes i don't see the point when i see a woodworker who wants to built a simple furniture with "rock solid"joints ever made....well ,i think,if we don't see the joint and we want to make it fast,easy and strong enough ,the domino system is the right one.

Marty
Title: Re: domino joint strength
Post by: rdesigns on September 06, 2012, 11:01 AM
Dominos may not be the strongest joints  but they are good enough for furniture making.They will last for years if we use them properly.This discussion,actually makes me think  about the difference in gluing strength between hide glue and modern glue.Hide glue may not be the strongest glue but it's good enough for furniture making and when it comes to repair ,it's easier .And it's easier too if we have to repair a floating tenon joint instead of a regular tenon joint,in my opinion.

Sometimes i don't see the point when i see a woodworker who wants to built a simple furniture with "rock solid"joints ever made....well ,i think,if we don't see the joint and we want to make it fast,easy and strong enough ,the domino system is the right one.

Marty

Good points--I suppose most woodworkers are like me to some extent; that is, I find that my projects are what I consider a balance between "best" vs "good enough."

Sometimes I do the best/strongest method because of the demands that will be imposed on the joints or materials, or just because I or the customer prefer that method.

Other times, I do what is "good enough"-- expedient for the sake of time- or material-savings. (I still use biscuits at times even though I have and love my Domino 500.) And I use the Domino in place of traditional M & T in most situations. (The frames of exterior frame-and-panel doors are an exception.)
Title: Re: domino joint strength
Post by: Tinker on September 06, 2012, 03:35 PM
Dominos may not be the strongest joints  but they are good enough for furniture making.They will last for years if we use them properly.This discussion,actually makes me think  about the difference in gluing strength between hide glue and modern glue.Hide glue may not be the strongest glue but it's good enough for furniture making and when it comes to repair ,it's easier .And it's easier too if we have to repair a floating tenon joint instead of a regular tenon joint,in my opinion.

Sometimes i don't see the point when i see a woodworker who wants to built a simple furniture with "rock solid"joints ever made....well ,i think,if we don't see the joint and we want to make it fast,easy and strong enough ,the domino system is the right one.

Marty

Good points--I suppose most woodworkers are like me to some extent; that is, I find that my projects are what I consider a balance between "best" vs "good enough."

Sometimes I do the best/strongest method because of the demands that will be imposed on the joints or materials, or just because I or the customer prefer that method.

Other times, I do what is "good enough"-- expedient for the sake of time- or material-savings. (I still use biscuits at times even though I have and love my Domino 500.) And I use the Domino in place of traditional M & T in most situations. (The frames of exterior frame-and-panel doors are an exception.)


Not being an experienced door builder or having had the fun of playing with a domino, my question is: why do you not want to use the domino for exterior frame and panel doors?

I want to build such a door for my equipment barn.
Tinker
Title: Re: domino joint strength
Post by: Sazerac819 on May 02, 2017, 02:16 PM
Reviving this topic. 

Any domino failures that have happened recently with the festool branded dominos? 

I see so many videos on youtube where people are putting together very large doors and heavy load bearing structures such as patios.  I include a video of a build that is a wrap around patio structure on the second floor!

Some seem to be using a combination of festool dominos and also their home made dominos as seen here:

http://www.youtube.com/watch?v=LIbnHtH6tR8

Here are some pictures of my current project.  I used the 14mm sipo festool dominos that I cut to 75 mm for 80 mm total tenon length (30 mm in the table and 50 mm in each leg) .

I have 2 dominos in each walnut leg and the 'waterfall' leg has 5 dominos. 

I'll be honest, when I dry-fitted the waterfall leg with the 5 dominos, I had a crazy hard time try to pull it back apart.  I required my wife sit on the end so I could slowly work it free again!

The table will not be heavy loading bearing, it will be along the wall in our dining area and used somewhat like a buffet table so just various food items and some dishes will be placed on the table on occasion. 

(https://c1.staticflickr.com/5/4180/34411100885_f6a275247e_b.jpg)

(https://c1.staticflickr.com/3/2881/34251930912_723a278359_b.jpg)

I do worry a little bit about my kids running/slamming into the legs and breaking the legs...  I guess we'll see. 

Cheers,
John
Title: Re: domino joint strength
Post by: grobkuschelig on May 02, 2017, 04:35 PM
I have not had any failures where I used Dominoes up till now.
But I only used the Domino on a couple of projects, since it is a recent addition to my tool collection.

What I try to do is make my own dominos if I use wood that is different than what the standard dominoes are made out of.
I convinced myself that having dominoes out of the same species, there should not be any problems with differences in wood-movement/shrinkage...  [scratch chin]
Title: Re: domino joint strength
Post by: Holmz on May 02, 2017, 07:55 PM
Was the failure in the domino, or the design, or the glue?
Title: Re: domino joint strength
Post by: Henrik R / Pingvinlakrits on May 03, 2017, 01:07 AM
I have never snapped a Domino. Not even one. I have done a couple of thousand Domino plunges and fittings since them machine came out. I have managed to break a few joints over the years - they have been either when using too thick a Domino in plywood/mdf or plunging to deep in one or both ends - or just being unlucky when putting something large together and accidentally dropping one side of a shelf before it has gone in all the way and the force has broken up the joint.

But never have I snapped a Tenon before the joint. Abiding by the Domino to material thickness ratio of 1:3 works well.

Same with wooden dowels and kitchen cabinets: it is almost scary how easy you can collapse a cabinet when you have removed the back and slam it. Flattening a kitchen in demolition takes no time.

But kitchens stay put for twentyfive years or more with heavy countertops and daily use. 

Some things don't need to be super strong, it just needs to stay together,  though it is nice when things don't discombobulate on their own volition.

I built an oak kitchen table for a family of four, with skinny legs*), extra tall since the guy who ordered it is very tall and wanted leg room. I Domino'ed the whole thing and made reinforcements where necessary since the legs are freestanding with an upper rim support on the table side. When his five year old daughter throws a tantrum she literally runs the table into the nearest wall [eek] and the legs occasionally catch something on the floor.

No problems, it is still slim and sturdy and not a wiggle in the joints two years of use and abuse later. 
I did corner brace the legs on the table side on the inside of the rim but I think that whatever the joint you need to look at the possible joint stress in daily/normal use and have some headroom on top of that but a lanky cabinet isn't meant to be tackled from the side - NFL/Oz rules style. 

*) the table, not the family.
Title: Re: domino joint strength
Post by: jobsworth on May 03, 2017, 07:11 AM
It's the glue that hold the joints together anyway, plus I never put 549 lbs on a joint that was domino'd.
Title: Re: domino joint strength
Post by: tjbnwi on May 03, 2017, 08:52 AM
I know I've installed over 100,000 Domino's not a single failure in any way.

Tom