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Discussion Starter · #1 ·
I was doing a little test of the strength of different joints.

I planed some hard maple down to 3/4 and ripped it to 5" wide. I made 5 different styles of joints you might find. T&G, 1/2 Lap, 1 Dowel, 2 Dowels, and a Biscuit. I then cut a slot right at the joint on the bandsaw, so each glue area was exactly 3" wide, to make each test start as even as possible.

We then tested them in tension to see which ones held up best.

As we were bolting these grips into the machine, I joked "Watch this thing pick this piece of steel right off the ground" I was more worried about the grips being able to hold onto the piece than it lifting it off the ground

Design Proj 001.jpg

Design Proj 004.jpg

Design Proj 002.jpg

Sorry, crappy cell phone pics.

Well it turns out, my first test, a T&G, picked the steel right off the ground, all 1500 pounds of it, before breaking, have u ever heard 1500 pounds of solid steel fall right in front of you without warning? We then bolted it down and continued the tests.

I dont have my numbers in front of me, but the 1/2 lap was the stongest, with an average of around 2700 pounds. The T&G and 2 Dowels were around 2400, the one dowel was around 1600, and the biscuit was around 1200. Keep in mind this is a 2.25 square inch area that the two boards meet.

Just figured someone might be interested in this.

I would have liked to do a Kreg screw, maybe some dowels AND half laps, Im sure I could come up with a few more fun things to try.

EDIT: To give credit, this was tested in the Norwich University Civil Engineering Lab
 

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Discussion Starter · #2 ·
A pic of the broken T&G, you can see that I cut it down so the effective joint was only 3" wide

Design Proj 003.jpg
 
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Discussion Starter · #4 · (Edited)
I cut it on a 7/8 dado blade, and left enough so the blade wasnt hitting the fence. So it was a 15/16 - 1" half lap. I can get you an exact measurement if you would want. In the next few days, I will get an exact measurement to measure all the glue surface on every joint, which seemed to be the weakest point on every joint, except the biscuit.

I could more or less re-glue every joint back to what it was, except for the biscuit, which tore the biscuit into shreds.

You can see the approx size of the half lap, and how I cut them down to 3", and also how the biscuit broke in the following pics

Design Proj 005.jpg

Design Proj 006.jpg

Again, sorry for the cell phone pics. If anyone is interested, I can get digital cam pics this weekend if they would like (I broke my digital cam, I break everything that isnt built "right")
 
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Discussion Starter · #6 ·
Thats cool, that 2nd picture looks like the wood stretcher i always heard about:laughing: GMOD
You heard about? You dont carry one in your trailer? Everyones got one, how do you fix the boards you cut short? You must be a HACKER!
 

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Cool. The machine they let you use had to be uber expensive. We have a universal testing machine in our lab for testing small pieces of steel and such nowhere near that size and I think they said it cost somewhere in the neighborhood of $20,000 :eek:

Nice choice on the grizzly straight btw. LOL
 

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Try a mortise & tenon with and without pegs.

Given the results I'd say that you must be using Elmer's white glue.:whistling

For a tight joint try Titebond II. For something with a little wiggle, Gorilla glue or a West System epoxy (the epoxy has a 48 hr. cure time). I'm sure that you'll see wood failure prior to adhesive failure.
 

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Discussion Starter · #10 · (Edited)
Cool. The machine they let you use had to be uber expensive. We have a universal testing machine in our lab for testing small pieces of steel and such nowhere near that size and I think they said it cost somewhere in the neighborhood of $20,000 :eek:

Nice choice on the grizzly straight btw. LOL
I think the machine cost more than the grizz...

Its basically a computer controlled version of a 250,000 pound shop press. Something most people have in the corner of their cabinet shop, nothing special...

Given the results I'd say that you must be using Elmer's white glue.:whistling
And yes, you must be a glue expert, good ol' elmer was the one filling the joints

Ive always been taught with elmers, I am intrigued, and now I think Im going to make a few joints exactly the way I made them, but use a few different kinds of glue and see what I come up with.
 

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Years ago I worked at a place with a 250K press brake, 4X8 on the table and a 3ft. stroke. They made sinks, stoves and cooktops in that area.

Coolest job that I ever had as an engineer. 70K sq ft of manufacturing space with all of the toys and an eccentric owner.
 
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