Regarding your poll regarding the strongest joint; more than one woodworking magazine has performed comparison tests on this subject and all have concluded that the half lap joint is the strongest by far. All other types of joinery paled in comparison, especially in regard to racking forces. Let’s face it……..we all know that face to face glue-up is the strongest of all other types of glue-up, no matter what the machanical additions (tenon, pocket joinery, etc.) may be.
nuff said.
Replies
"nuff said."
In terms of immediate ultimate strength, perhaps. What really matters, though, is how the joint holds up under day-to-day abuse over the years. A more realistic comparison would be to do the kinds of repetitive stress tests that Consumer Reports does. The results of that kind of test could very well be rather different.
-Steve
A half lap is stronger than a full mortise and tenon? Given the same wood dimensions??
That seems questionable.... magazine survey or not.
dan
It's not a survey, it's actual lab test results.
-Steve
Is that something you could read how they conducted the test?
dan
There are articles in the November 2006 and December 2007 issues of Wood magazine. They used standard Instron-type test equipment to measure the stress/strain properties of the joints. The print articles have detailed info, but you can also see videos of the November 2006 and December 2007 tests.
The take-away lesson from these tests is that the joint strength is pretty much directly proportional to glue surface area. What the tests don't show is how the joints react to repetitive stress, the kind that you'd find in a drawer or chair. That's the kind of Consumer Reports-style testing I alluded to in my earlier message in this thread.
-Steve
Thank you Steve. I think I'm going to take a look at them it looks interesting to me.
dan
I don't use glue on my "fine" furniture.Countless artisans throughout history have also made joints with no glue, little glue or some animal byproduct that isn't exactly two-part epoxy. Half-lap, eh? LOL- seriously, what actually is the strongest JOINT?-Bobro
Bo,
My vote is for a wedged mortise and tenon, for frames; wedged dovetail for case corner joints. Same as countless craftsmen with no glue have used. Some of those complicated oriental scarfed interlocking keyed joints (designed for "ungluable" woods) are right up there I guess, but I have little experience with them.
Ray
Maui wowee?
Yes, glue surface area pretty much determines the outcome of these tests, but as has been pointed out the lack of repetitive testing undermines the applicability to some degree. The other factor that is related but not exactly the same as repetitive testing is the impact of glue deterioration over time. The half lap depends almost entirely on glue. Reduce glue strength 50% and the joint strength would be reduced by a closely proportional amount. The same isn't true for mechanical joints such as the dovetail and the mortise and tenon joint.
I'd bet that over a 50 or 100 year time frame the traditional dovetail for drawers and mortise and tenon for frames (and legs to rail) will outperform half laps by perhaps an order of magnitude. Pretty hard proposition to test since I doubt we have sufficient data to use survivability over time as a guide.
Without the necessary data, I'll let others make kitchen cabinets with half laps--they may well survive the 10 or 15 year expected design life. But for furniture that I would hope my grandchildren's children will have to decide what to do with, I stick to joints that aren't quite so glue dependent. After all, the only glue with any 100 year history is hide glue.
And as far as the most demanding application, chairs, I'd really want to know the extent of the makers product liability insurance coverage before I sat for any length of time in a chair put together with half laps.
Edited 2/7/2008 10:27 am ET by SteveSchoene
Exactly.
Strongest joint? No such thing, IMO. Strongest joint for a particular application? You bet. It all depends on how the load is going to be applied.
Paul
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