Rabbet or Double Rabbet joint.......

[Bill Huber]

The double rabbet joint

has

an even greater glue surface area than a

rabbet joint.


Forgive my ignorance on this but.

I have been reading a lot about joints and how to make them. Just about everything I read makes the same statement. The double rabbet has more or much more or even twice as much glue surface as the rabbet.


I just can't see it, where is my thinking off on this one, to me they both have the same surface area in the joint. Now I really can't say why but the double rabbet does look stronger then the rabbet.


This drawing shows 2 1x1 boards with a rabbet and a double rabbet.


67458

[John Lucas]

I'm with you. To me, the single rabbet has the best chance at being a strong joint. Now if you reversed the "double rabbet" it would be a drawer lock joint and might be stronger for strength in both directions (i.e open and close.) So much of this is anyone's guess. I dont think there are double blind tests or anything else that would stand up to questioning.

[Cliff Rohrabacher]

the single rabbet has the best chance at being a strong joint.

And less opportunity to mess it up.

[pat warner]

Joints with more intimacy, articulation and mechanics resist stress better than those that don't. Glue surface is only one important variable.
Good dovetails, e.g., stick together very well with no glue at all.

Routers (http://www.patwarner.com)

[John Schreiber]

I just can't see it, where is my thinking off on this one, to me they both have the same surface area in the joint. Now I really can't say why but the double rabbet does look stronger then the rabbet.
Good observation. It seems like it would be stronger, but there's no reason I can see why it would be.

Testing is the only way to tell.

[James Phillips]

The double rabbet joint

has


an even greater glue surface area than a

rabbet joint.


Forgive my ignorance on this but.


I have been reading a lot about joints and how to make them. Just about everything I read makes the same statement. The double rabbet has more or much more or even twice as much glue surface as the rabbet.


I just can't see it, where is my thinking off on this one, to me they both have the same surface area in the joint. Now I really can't say why but the double rabbet does look stronger then the rabbet.


This drawing shows 2 1x1 boards with a rabbet and a double rabbet.


67458








You are correct they have the exact same surface area. Think the single rabbet would be stronger because it would likelu be better made. Neither joint supplies any mechanical holding force like a dovetail or lock miter.

[Jason Beam]

Same surface area ... absolutely right on, there.

The double may be stronger due to the number of friction/pivot points when a racking force is applied. On a single, the only real pivot point is at the far corners of the joint. On a double, the pivot point has to change in the travel of the racking.

Imagine trying to collapse the 90 degree corner in the picture like closing a book. The pivot point on the single rabbet joint would be exactly where the arrow is pointing in that picture. With the double rabbet, it would start there, but the lip of the 2nd rabbet (right in the center of that joint) would be sliding, scraping, jamming against the inside of it's mating face, which would move the pivot point. This actually happens several times, the point goes back and forth between that mating surface and the original pivot point. This swapping introduces resistence, making that joint resist the forces a little more.

Expanding the 90 degree joint is similar, except the points swap between the outer edge and the mating faces.

It's kind of like the double rabbet is a rudimentary form of a keyed joint. That extra step creates a very simple keyed interface. Not nearly as positive as a drawer lock or lock miter or spline joint, but an improvement nonetheless.

This is how it works in my head, anyway.

Edit: This all assumes there is more than one corner to this device. As shown in the picture, a single corner isn't stronger. But combine 4 of these corners and they help with that moving pivot/friction point I was trying my best to describe above. The other corners would prevent a simple movement, it'd be a compound motion. Not just a rotation, but the pieces would also be pushed around by the opposing corners. The isolation of a single joint makes the two identical.