Wood Mag. Joint Torture Test ?

[Doug Shepard]

The current issue of Wood Magazine has a joint torture test where they checked how many Lbs of force were required before the joint failed. Half Laps fared far better for door (frame type) joints than the other 3 types they tested (mortise & haunched tenon, stub tenon & groove, cope & stick). In their opinion this was due to this having more glue surface than the other types. So I'm left curious and disappointed that they didnt also include bridle joints in the test. Does is naturally follow that this would be twice as strong as the half-laps or is there some sort of diminishing return as the wood thicknesses goes from 1/2 (in the half-laps) to 1/3 (in a bridle)??? Anybody seen one of these torture tests that had both half-laps and bridles and recall how they compared?

[Gary Muto]

The thing that disappointed me about that article was did not take into account stabiltity of the wood or deterioration of the glue. If a joint fails that catastrophically, I don't think I'd blame the work as much as what it was subjected to. :eek:
While the wood may be the strongest in a 1/2 lap joint, I'm still biased toward Mortise and tenon joinery. It appears to be a good compromise between strength, stability (warpage) and long grain glue surface area. Just my opinion. Put a peg through it and it will hold up if/when the glue fails. I think that joint is a sign of craftmanship as well.:cool:
BTW, based on the above, i would rather have a bridle joint than a 1/2 lap IMHO.

[Bruce Haugen]

They didn't test the half lap against the biggies of the joint world: full mortise and tenon. I've never used the little stub tenons they tested. Even in small projects, the mechanical strength of the full M&T is surely stronger than the half lap. And Doug is right about the bridle joint, with twice the glue area.

This article is a shoe-in for straw man of the week argument.

Bruce

[Fred Voorhees]

You can see a video of the torture test at the following address. Look under the current Wood magazine issue section.

http://www.woodmagazine.com/wood/file.jsp?item=video/player&temp=yes

[Chris Friesen]

They didn't test the half lap against the biggies of the joint world: full mortise and tenon. I've never used the little stub tenons they tested.

No kidding. The incremental cost of making a longer tenon is hardly anything.

I read somewhere that the "traditional" tenon width is two-thirds the width of the tenon stock, it's thickness is one third the thickness of the stock, and it's length is five times its thickness.

Of course this varies if you're doing very wide tenons or very long through tenons, but it's a place to start.