Strongest Joint

Alex Reid

Member
Messages
739
Location
Zushi, Japan
I was thinking recently about joint stregth and took a look at FWW to see what they had to say. I found the following test and poll.

Here are the results from a Fine Woodworking test on joint strength using a hydraulic press. The press stress tested for racking on a 90 degree joint constructed of 3/4 thick x 2.5 wide x 8 long inch cherry stock. Placing the stock on an end-to-end diagonal and applying vertical force down to the breaking point of the joint.

1. HALF LAP 1,603 lb.
2. BRIDLE 1,560 lb.
3. SPLINED MITER 1,498 lb.
4. 3⁄8-IN. MORTISE & TENON 1,444 lb.
5. 3⁄8-IN. FLOATING M&T 1,396 lb.
6. MITER 1,374 lb.
7. 3⁄8-IN. WEDGED M&T 1,210 lb.
8. 3⁄8-IN. PINNED M&T 1,162 lb.
9. 5⁄16-IN. M&T 988 lb.
10. BEADLOCK 836 lb.
11. DOWEL 759 lb.
12. ¼ -IN. M&T 717 lb.
13. POCKET SCREW 698 lb.
14. DOMINO 597 lb.
15. BISCUIT 545 lb.
16. BUTT 473 lb.
17. COPE & STICK 313 lb.
18. STUB TENON 200 lb.

And here are the results of a readers poll in FWW forum Knots on the the strongest joint

1. M&T
2. Half Lap
3. Bridle
4. Pocket Screws
5. Floating tenon
6. Other
7. Miter
 
What I have yet to see (and I've seen articles like this a few times) is a test/article on (a) how much joint strength is good enough, and (b) some way to test how joints last over time.
 
I notice that the single criterion for the lists is strictly strongest joint, and if it is defined very specifically, you can test to that criterion and get your answer.

I think the FWW poll came up with different answers because people factor other things in. The mortise and tenon may not be as strong as a half lap but the M&T looks better than a half lap, in most people's eyes, so they favor it.

And people should factor in other things besides just the strength. As Art pointed out, once you have a number of joints that are "strong enough" you need to make your choice from that group based on other factors. And that's where the M&T wins out.

Mike
 
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If a half Lap is the strongest then what about a full lap joint..:huh::dunno:

It won't be as strong, since it doesn't have the help of the joint shoulders.

Lap Joint

image.giflapjoint






Half Lap Joint


image.gifhalf%20lap
 
Interesting.

I wonder how the loading was applied.

I would love to see test results for sever common joints with different loads applied.

Load types:
Tortional (likely this is what was applied to the above tested joints)
Tension (pulling apart)
Shear
Compression

I have to agree with "How strong is strong enough" - then apply asthetics to the joint.
 
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