Teardrops n Tiny Travel Trailers

Woodworking Joints Torture Test - Wood Magazine Nov 2006

Are pocket screws stronger than dowels? Which of the woodworking joints give the most strength? Do screw add any strength to a joint?
For the "Wood Joint Torture Test" in WOOD Magazine issue #173, they created and then destroyed more than 100 joints.
Wood Magazine Shear test:
Mortise & Tenon Joint took 1,005 lbs/force - over double to triple the force to break compared to other joints.

Wood Magazine Pull Apart test:
Biscuit miter joint 220 lbs/force; Dado 559 lbs/force - screws did not help.
For a Mortise & Tenon Joint, the wood failed but not the joint. It took 4,733 lbs/force nearly 2½ tons to pull apart.

Clearly, this test shows that the Mortise & Tenon joint is superior to other joints

droid_ca wrote:
Clearly, this test shows that the Mortise & Tenon joint is superior to other joints

True enough, but you need to consider the expected forces a joint will be subjected to. If an easier method will provide the results without an unacceptable drawback (esthetics for example) then that may be the right one for the job.

-Greg

Greg M wrote: True enough, but you need to consider the expected forces a joint will be subjected to. If an easier method will provide the results without an unacceptable drawback (esthetics for example) then that may be the right one for the job.

My motto: "Overkill in moderation".

Cheers,

Gus

A mortise and tenon is, clearly, a superior joint. It, along with the dovetail, is the darling of the woodworking set. The question is, do we want to use them to build a trailer? Stick building a trailer with mortise and tenons would be labor intensive to the max. Given reasonable care, I think a trailer built with pocket screws would last as long one with fancy joinery.

I guess I should of been a little more clear I never said that the mortise and tenon was the best it was part of the article I just wanted to share it with all of you as there were people a while back asking how strong certain joints were

droid_ca wrote:I guess I should of been a little more clear I never said that the mortise and tenon was the best it was part of the article I just wanted to share it with all of you as there were people a while back asking how strong certain joints were

But it is the strongest! It's just that everything in life is a compromise and good enough is sometimes, well, good enough.

Cheers,

Gus

droid_ca wrote:I guess I should of been a little more clear I never said that the mortise and tenon was the best it was part of the article I just wanted to share it with all of you as there were people a while back asking how strong certain joints were

I think that you should add that a good mortise and tenon joint is the strongest joint. Building one with the correct tolerances is the challenge for most including me - at least those of us that don't have a Festool Domino (although technically it makes a floating mortise and tenon joint.) Where it works, butt joints with pocket hole screws are quickest and strong enough for most teardrop construction.

I wonder if the joinery in TD building makes much difference since the frame is skinned, glued, covered, epoxied, etc.

Where is the strength needed?

Tom

I don't think the strength of wood framing joints has any relevance to teardrops - it is the joint between the various sheets of plywood that matter and in most cases, with the possible exception of roof spar to side wall joints, having any end connections between the framing members isn't needed.

And on that subject, building a self-supporting framework of timber pieces and then afterwards skinning it in plywood is just a waste of effort -it's just a case of folks thinking they are building a house, but forgetting that you can't buy single sheets of plywood large enough to build houses from.

I should say that I admire those who can make wood joints to this level of quality, and I love looking at them, but they just aren't needed structurally.

The commercial RV's I have seen and assisted in dismantling and/or remodeling are held together with a handful of staples and a little glue. I over killed building mine by making all wood beams in a tee with opposing grains and rotating wood dowels and biscuits every few inches. But then I used all cedar construction and felt the need for the extra effort for strength. Were I building again I would plane all my wood to 1/2 inch instead of 3/4 inch except for the ones around windows, doors and vents and believe it would be more than strong enough when the sandwich is completed. I have only 6 bolts to hold my torsion box to the trailer and the only screws are to hold on my aluminum trim. It has been over 9000 miles this summer on a variety of road conditions without any issues so I guess it is more than adequate in structure.