Comparative Wood Joint Strength

[Jeff]

Thought you folks would be interested. The article is in "FineWoodworking", #203, February 2009 (Taunton Press).

It reminds me of McRabbets choice of a half lap joint for door frames in an outdoor project that he was commissioned to build for a local park.

There are some surprising winners and losers as well. Hope it helps us all build better stuff and make informed choices for our joinery and its intended application. :help: :dontknow: :icon_scra

 

[DaveO]

That was an interesting test. Not without it's testing method flaws, it really does show the strength of modern wood glues. I am suspect of the butt and miter joint ratings compared to the other joint methods that have physical support other than the glue. I am glad to see that with modern ww'ing glues even the weakest joint method takes 400+ lbs. of pressure to break it.
I just had a biscuit joint failure that really was a wood failure...due to the weakening of the wood by cutting the slot for the biscuit. Glues will hold better than the wood will.

Dave

 

[jeff...]

Speaking of this what do you guys use to edge join wood planks together to make a panel? Dowels / Biscuits / Splines or nothing but glue?

 

[Canuck]

Speaking of this what do you guys use to edge join wood planks together to make a panel? Dowels / Biscuits / Splines or nothing but glue?

I am probably the loner here, but I use 3/8" dowels in 4/4 stock when I glue up a panel. I find that alignment is a no brainer when I use dowels. (Not looking for more strength necessarily, as today's glues are tough!)

Just a personal preference.:wsmile:

Wayne

 

[DaveO]

Speaking of this what do you guys use to edge join wood planks together to make a panel? Dowels / Biscuits / Splines or nothing but glue?

Just glue, if you can stack your boards on top of each other in a vertical orientation and the stack doesn't fall...you're good to go


Dave;-)

 

[Tar Heel]

Glue only. Haven't had a failure yet. I use to use biscuits but stopped that long ago.

 

[Travis Porter]

I started off using dowels and then switched to biscuits, and now nothing. The only reason I did it was for alignment, but after screwing up and cutting through a couple of biscuits and dowels, I decided I could sand or plane out my misalignment easier than trying to hide a showing biscuit or dowel.

As for the FWW article, I really don't see that it offers much if anymore insight than the tests they did in August of last year.

 

[Gofor]

For edge joining I just use glue. I do spend a bit of time making sure the edges are light free when viewed toward the sunlight and have that "suction" feel when rubbed together.

Go

 

[PChristy]

when I worked in a local door factory that built interior/exterior solid fir doors all they would do was just glue the joints - ok I guess for interior but for the exterior I noticed that the one I got from them (at a great discount by the way) pulled away from the joints - could have been from the heat build up between the door and storm door:dontknow:

 

[cpowell]

...but after screwing up and cutting through a couple of biscuits and dowels, I decided I could sand or plane out my misalignment easier than trying to hide a showing biscuit or dowel.

I had the same experience and no longer use biscuits/dowels. :no:


Chuck

 

[JimD]

I like the article better than the similar one in Wood. Wood used 2 inch wide pieces which made biscuits look really bad because the biscuit was so small. The FWW comentary wisely comments that their tests do not consider wood expansion/contraction which would likely affect butt joints and miters more (because there is no mechanical interaction). They are using a pretty simple test setup and at least FWW tested racking (instead of pull apart). Real life loads are not so simple but the test would be significantly more difficult to consistently set up.

I would further speculate that a little twist - the load not applied perfectly in line with the joint - is also likely to move mortise and tenons up and half lap down.

I use biscuits to make large surfaces like table tops. If it's something small like a raised panel blank, I use nothing. The bigger the surface, the harder time I have keeping things aligned during glueup. I have not seen any telegraphing of the biscuit but I have located one too close to the edge of an oval top.

Jim