"What's the Best Wood Joint || Insanely Strong Joinery!" YouTube

[reible]

What's the Best Wood Joint || Insanely Strong Joinery!

This is one of the guys I follow on youtube. Not always for his woodworking.........

Anyway I expect a few people here will not expect the results shown and that could be OK

https://www.youtube.com/watch?v=CE147Ow ... oodworking

What is clearly missing is application, like when do you use a particular joint for a drawer vs for a similar frame for say a cabinet.... well you get the idea I hope.

Ed

[algale]

I'm surprised by the results.

[Hobbyman2]

All ways been a fan of splined miters and box joints .

[SteveMaryland]

Very informative video, thank you Ed for bringing it to our attention!

Geometry and workmanship account for a lot of the strength difference. Glue joint shear strength goes up as the glue line gets thinner.

I have used splines but not on mitered corners. The fit between spline and kerf needs to be close. 4X thin splines made of a non-grained material such as acrylic or maybe aluminum, combined with a close-fitting kerf, would be the best. I like the sled he used to cut the kerfs.

That's the great thing about Youtube - somebody somewhere on Youtube has already done the gruntwork, and we get the free data points!

[bainin]

There's probably a number of things going on we don't see from just the fracture point and would require something like a stress-strain curve (modulus) to understand better.

Its likely that joints with more than just glue as a strengthening feature will exhibit 2 breaking points. One for the glue and 1 for the (dowel, plastic thingie, biscuit , interference joint etc).

He should have done some joints without glue and just the "adder" part like dowels etc to understand this better.

I really like the look of the miters with corner inserts...I need to play around with that a bit.

b

[Hobbyman2]

There's probably a number of things going on we don't see from just the fracture point and would require something like a stress-strain curve (modulus) to understand better.

Its likely that joints with more than just glue as a strengthening feature will exhibit 2 breaking points. One for the glue and 1 for the (dowel, plastic thingie, biscuit , interference joint etc).

He should have done some joints without glue and just the "adder" part like dowels etc to understand this better.

I really like the look of the miters with corner inserts...I need to play around with that a bit.

b

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I played around with the box joints and drilled holes down from the top and up from the bottom into the joint , than added a dowel into the hole , looking down from the top it looked like a hinge pin, cutting splines into the corners of cabinet door frames turned out to be very strong .

[Ed in Tampa]

Interesting! Thanks for posting

[chapmanruss]

Thanks, Ed for the informative video. Like the others I am surprised that the winner was something that I consider a nice decorative joint.

[BuckeyeDennis]

Everything else being equal, and ignoring the difference in end-grain effects, I'd expect the miter joint to be roughly twice as strong as the butt joint.

Here's why. Because the miter joint is cut is on a 45 degree angle, its glue joint is 1.41 (square root of 2) times longer (in the direction of board length) than that of the butt joint. Now in your mind, divide the glue surface of each joint into a rectangular grid, each with the same number of "cells". Then, compared to the butt-joint geometry:

• The center of a given miter-joint cell is 1.4x farther away from the "fulcrum" at the inside corner of the joint. That's like putting a cheater bar on a socket wrench handle, and it gives the glue-joint cell a 1.4x greater lever arm.

• The glue area of a given miter-joint cell is also 1.41 times as large. That gives it 1.4x more holding power.

These beneficial effects are multiplicative, so they combine to give a joint that is roughly twice as strong as a butt joint. Simply because of the glue-joint geometry.

Now as SteveMaryland pointed out, the thickness of the glue joint will probably affect it's strength. With a single joint, as shown in the video, it's easy to get a perfectly tight joint. But if making a drawer box, for example, that's a whale of a lot harder to do. And if the joints are imperfect, they might not fare so well in strength testing.

[algale]

Everything else being equal, and ignoring the difference in end-grain effects, I'd expect the miter joint to be roughly twice as strong as the butt joint.

Here's why. Because the miter joint is cut is on a 45 degree angle, its glue joint is 1.41 (square root of 2) times longer (in the direction of board length) than that of the butt joint. Now in your mind, divide the glue surface of each joint into a rectangular grid, each with the same number of "cells". Then, compared to the butt-joint geometry:

• The center of a given miter-joint cell is 1.4x farther away from the "fulcrum" at the inside corner of the joint. That's like putting a cheater bar on a socket wrench handle, and it gives the glue-joint cell a 1.4x greater lever arm.

• The glue area of a given miter-joint cell is also 1.41 times as large. That gives it 1.4x more holding power.

These beneficial effects are multiplicative, so they combine to give a joint that is roughly twice as strong as a butt joint. Simply because of the glue-joint geometry.

Now as SteveMaryland pointed out, the thickness of the glue joint will probably affect it's strength. With a single joint, as shown in the video, it's easy to get a perfectly tight joint. But if making a drawer box, for example, that's a whale of a lot harder to do. And if the joints are imperfect, they might not fare so well in strength testing.

Really insightful observations, Dennis! Not only on the math/engineering but also the real world difficulties of getting more than one "perfect" miter joint!