Domino joint test in FWW...

[The Toolman]

The piece of wood used could have a lot to do with the result. If the grain was close to the edge etc. Hard to make scientfic tests with alot of variables in wood.

 

[Dave Ronyak]

I just received that FWW issue after my earlier post here.  If you look at the photos in FWW and read the accompanying text, the authors point out that many of the joints failed due to splitting away of the edge region of the stile.  In other words, the design of the joint used caused localized loading adjacent the edge of the stile to exceed the inherent strength (resistance to splitting parallel to the grain) of the stile.  If I was seeking maximum strength against the type of loading used in the test, with Dominos I would use two of them, and probably a longer one nearest the outside edges of the pieces being joined.  This would effectively somewhat replicate use of an integral haunched tenon.  My hunch is that simply moving the single 10mm Domino tenon off center toward the outside edges of the rail and stile would have increased the strength of the joint in this type of test.  Applying glue only in the bottom 2/3 of the Domino mortice would also be a test of interest to me; I think it could result in increased strength in this particular type of test.

Dave R.

 

[fshanno]

Here's an interesting thing I found on the Festool New Zealand site.

New Zealand strength test

It's a bigger joint and had 3 dominos but it held 5 TONS!  HELLO! 

 

[Dave Ronyak]

Note that in the NZ strength test the load is being applied to the samples being tested oppositely to the test in FWW.  The highest tensile stress levels in the NZ test will occur at the inside corner of the joint, with compression occurring near the outside corner surfaces.  In contrast, in the FWW test setup, the highest tensile stress levels occurred at the outside corner, thus likely making it easier to start tearing apart the wood of the stile.

Dave R.

 

[nickao]

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

I am not. I have used loads of pocket screws and they are strong when used with glue and I mean strong.

The reason I do not use them is for looks, not that they have no strength. Many think of pocket screws as the easy way out, well when used in conjunction with other joinery methods the pocket screws have served me well. And I defy you to even find them on the cabinets I have made when using them.

They are not as crude as some think.

This strength thing is overblown a little isn't it? All the joints have their place and are plenty strong for what most of us build.

I Base my  joint selection on certain priorities dictated by the project, not just the on the strength of the joint. Actually, strength is never my first consideration unless it is a structural application. I usually pick the best looking, then the fastest and then strength last.

Though I do not have one, the Domino seems to be perfect for many projects. The joint it makes it looks great, it is fast to make and strong enough for most any project, even going by these test results.

 

[wnagle]

Yes Pocket screws are strong... maybe compare two pocket screws to two dominos... or one domino to one pocket screw in the center... I bet that would change the results a bit.

 

[fshanno]

Pocket screws are very strong.  Hurricane Ike blew a door off an outside cabinet I built.  The face frame was assembled with pocket screws and attached to the carcass with pocket screws using no glue.  The two hinges tore out of the style taking sizable chunks with them but other than that one style the face frame was undamaged.  I just unscrewed the face frame from the cabinet then the style from the face frame and put in a new one.

But Dominos held their own as well.  The door was blown about 30 feet across the yard and stopped when it hit a fence.  It was scuffed up but other than that it was ok.  It was built with 2 8x40 dominos in each joint.  I used two to get better alignment because the rails and styles were 3" wide.  The panel was not glued other than a tiny amount that spilled into the slots on the styles where they ended in a mortise.  100 mph max winds with gusts higher in our town.

Surely Festool USA will find out about this article.  To me it makes the Domino look a bit like an also ran.  I wonder if Festool will respond in some way.  I'm sure they don't want to pick any fights but it seems like you'd want to defend you're $700 baby.

 

[Matthew Schenker]

Good Afternoon,
I finally had a chance to read the article yesterday at Home Depot (I no longer have a subscription to Fine Woodworking).  I was surprised to see the results.

On one hand, it was disheartening to see the Domino way down on the strength scale.  But on the other hand, I was happy to see bridle joints way up there!  I've always been a big fan of bridle joints for mirrors, doors, and other frame-and-panel work.  The vast glue surface of a bridle joint is nice to work in, and gives me a sense of confidence.

On a related topic, I do feel that joint tests can sometimes can leave us thinking that certain joints are inferior, even though the strength they offer is far above what we'll ever actually need.  For example, I've long ago moved away from using biscuits.  However, there are certain applications where biscuits are good enough.  Let me admit here that, about 10 years ago, back when I started doing woodworking and knew nothing about joinery, I built some pieces using dominos.  Those pieces are still holding up just fine.

Please do not take this as an endorsement of biscuits!

Thanks,
Matthew

 

[nickao]

"  Let me admit here that, about 10 years ago, back when I started doing woodworking and knew nothing about joinery, I built some pieces using dominos. ". 

I think you meant biscuits Matthew.

 

[Matthew Schenker]

"  Let me admit here that, about 10 years ago, back when I started doing woodworking and knew nothing about joinery, I built some pieces using dominos. ". 

I think you meant biscuits Matthew.

Yeah, I meant biscuits!!  I guess my thinking has been changed so much using the Domino, I think of that method when I think of joinery these days.
Matthew