I made a new joint

[David Nebenzahl]

Actually discovered a variation of a joint I discovered some time ago.

Way back in the 19-ought-80s, I invented a 3-member lap joint trying to join three stretchers on a small table (I made the joint but never finished the table). It was published by /Fine Woodworking/ in their "Methods of Work" column, and later included in a couple of their collections of /Proven Shop Tips/:

a few days ago I sat down to design some parts to the wooden tripod I'm building, and remembered this joint. However, after making some sketches and a cardboard mock-up, I realized that this joint could be made much more simply: the original joint is stronger since it has a larger glue surface area, the new variant is much easier to make. In fact, I did the whole thing on the table saw, where in the original joint you have to chop out half of the waste. And I'm not the best wood-chopper-outer in the world, I'll admit. Hard to keep those surfaces flat enough for gluing.

The new joint is an interesting little puzzle that I haven't completely figured out yet. Because of its asymmetry, it needs to be made oversize to cover the needed width. The finished joint looks nice, though not as interesting as the original with its angular inlets.

[RicodJour]

I like the original design, too. It's got a Chinese/Japanese flavor to it. Seems to me you could use a jig and router and knock out either joint fairly easily with just a little bit of handwork.

Are you still in Flagstaff? I rode through there on my bicycle on my way cross country back when your Methods of Work tip appeared. Great area.

R

[Morris Dovey]

Sometime over the summer (or perhaps next winter) I think I'll have to try writing a short CNC router program for a close variant of the original. It's just too interesting to not try! :)

Thank you for sharing both joints.

[Tom Veatch]

You say you've actually made the new variation of the joint using a table saw? How about posting a picture or a dimensioned sketch of the side not shown in the sketch in your link. A Sketch-Up model would be preferred.

I agree it's a puzzle. I've failed so far to lay out an arrangement that can be cut with a table saw where the side not shown in your sketched plan view isn't full of gaps, voids, and/or mismatched edges.

Tom Veatch Wichita, KS USA

An armed society is a polite society. Manners are good when one may have to back up his acts with his life. Robert A. Heinlein

[Morris Dovey]

Good catch - I fired up DesignCAD and confess that I couldn't make the geometry (as drawn) work either. Perhaps Dave is remembering another joint...

[Lowell Holmes]

:-)

[Lowell Holmes]

I was successful in posting a pdf of the joint. The joint needs to be modified in order to fill the voids. That would be easy to do. I'm not sure it could be done on a table saw.

The sketch shows a single part and then three parts assembled. And then I showed a rotated view of the same assembly.

I think it is an ingenious solution.

[Morris Dovey]

Me too - but when I tried to do the modification (by shifting the "center" toward the side), I still couldn't make it work. I'm not certain that I couldn't have done better with another cup of coffee, but...

I think the original joint was the truly ingenious one. So ingenious that I've stashed it in my "must try" collection (even though I don't build furniture).

[Lowell Holmes]

I tend to try keeping things simple. I might very well use the second method and glue blocks in the void. You could also taper the boards to fill the void. You might even make it a design element.

[RicodJour]

Obvious solution - get a bigger cup. ;)

R

[Lowell Holmes]

Obvious solution - get a bigger cup. ;)

R I tried that also. I think the original joint with some hand work is the way to go. It would not take much time at all to do. I may go to the shop and try one just to see. If I do, I will post a picture.

[Lowell Holmes]

Obvious solution - get a bigger cup. ;)

R I went to the shop and made a rough try at David's original joint. I had to make a slight change from what my understanding is, but it did make up. The work I did is rough and not close tolerance, but you can see the joint works. I posted photos in abpw news group.

[David Nebenzahl]

On 5/18/2009 2:06 AM Morris Dovey spake thus:

My bad; I probably should have been clearer.

The joint is shown correctly, and the finished joint as well. But what I left out is that the joint will have voids on the sides. (This is what I meant by the "puzzle" part of this joint; I still haven't figured out how to lay it out to minimize the waste, or to maximize the width.)

The original joint doesn't have this flaw, but then it's a lot harder to make. (Unless, of course, you set up your CNC machine to cut it. But even then you'll have to finish the sharp corners by hand.)

[David Nebenzahl]

On 5/18/2009 12:58 PM Lowell Holmes spake thus:

Now that you've made it, you should try to make some variations with n members (4,5,6, etc.). It'll work with any number of pieces (well, within reason).

I'm just afraid that the 4-member one will have a center that looks like a swastika ...

[Morris Dovey]

Clarity is good - or so I was telling myself at 4am :)

Actually, you did a such a great job with the original that I'm not very concerned with the second (but put me on your mailing list for when you make the second work without voids!).

I /will/ eventually CNC cut the original - and won't need to finish the sharp corners by hand. The top three photos at

CNC routing done with a 1/32" (0.79375 mm) bit, which would leave a 1/64" radius at (only) the three inner points. If you didn't already know what to look for, they'd look sharp. I've seen 1/64" bits advertised, but why bother? :)

By the way, the photo at the bottom of that page shows a 1/4" tenon cut on the end of a 1/4" thick board - with a shoulder all the way around. :)

And to return the favor you've done me, I have a lap/scarf joint you might find interesting. It demonstrates a bit of what becomes possible with CNC cutting.

(to get even with you for not telling me about those voids!), at

're photos of a DIY CNC router with a 1/4800" step size intended just for joinery operations - and I think you might have a lot of fun with something like. Best off all, it took less than a half-sheet of

3/4" Baltic birch...

[David Nebenzahl]

On 5/18/2009 7:09 AM Morris Dovey spake thus:

Thanks. Since you like the design, you might find this variation interesting:

up with it while doodling designs for the tripod, but after making a mock-up decided it was too much work for this project. I like the circular motif.

Put that in your CNC program and smoke it!

[RicodJour]

How would you assemble that joint? It seems that you'd need fairly loose fitting joinery and fairly thin pieces.

R

[Robatoy]

Not to mention the amount of wasted material to make it (out of one piece)

[RicodJour]

Hmmm. You've given me an idea. Just scribe some lines on some wood to make the joinery look complicated. Sure would be easier.

R

[David Nebenzahl]

On 5/19/2009 5:46 AM RicodJour spake thus:

What do you mean? It should fit tight as a drum.

It is a bit of a puzzle, so maybe you just need to visualize how it comes together. (Took me a while, and I'm the one who dreamt it up.)

There is some waste, sure, since the legs are narrower than the center of the joint, but that happens many places in woodworking. We love to waste wood!