# double dado cross half lap joint?



## woodnthings

I've been experimenting with this joint for a knock down table. No hardware allowed. My dado method was to use a narrow setup and flip the boards over to keep it centered....somehow that isn't working as accurately as I 'd like and I get confused whether I'm measuring the slot or the lapping piece. I don't expect an answer or solution, but I'm probably gonna go a 3/4" stack instead of the flip method. I realize I'm makin' it more complicated than just one dado up and one down and interlock the boards, but I see this a somewhat stronger and resistant to racking.

First attempt photos:


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## mdntrdr

*That's a cool joint!*

Looks like it would resist racking better than a standard cross lap.

Lots of... no glue surface. :huh:


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## jschaben

:thumbsup:I like it.

Looks like you are doing the dado's with a stack and the half laps with the router. I think I would be inclinded to do both with the router. Guide strips and a bushing for the router, switch the bushing add a stop to get the half lap, maybe need to switch bits too but would keep everything centered. I think I would probably make a "U" shaped jig to ensure the guide strips are the same on both sides of the board.


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## sanchez

Nice joint!


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## woodnthings

*yeah, it's cool but*

everything has to be dialed in spot on, because each time you flip it over to make the dado on the other side, you X2 the mistakes, in my case, or depth of cut. Width wise the dado is more managble, but still requires 2 passes and therefore 2 fence settings. I plan on making 3 or 4 of these so, I'll have to practice, practice..... :yes: bill


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## woodnthings

*Practice...practice....*

Like marriage, 4th time is a charm...:blink:
Gettin' closer to no gaps or almost perfect:


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## Improv

Your sketch looks like your legs are angled in slightly, but your cuts are square. Am I seeing those correctly?

My suggestion is to build a dual-vertical router table with facing bits to run your board through so you don't have to flip anything. Your bits would probably need to rotate in the same direction ('down' on the feed side) for safety and accuracy.


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## woodnthings

*that's the photo distortion*



Improv said:


> Your sketch looks like your legs are angled in slightly, but your cuts are square. *Am I seeing those correctly?*
> 
> My suggestion is to build a dual-vertical router table with facing bits to run your board through so you don't have to flip anything. Your bits would probably need to rotate in the same direction ('down' on the feed side) for safety and accuracy.


The legs are square.

As far as the dados I am considering a router with an edge guide or just a router table. 
The most direct way is to be able to center both sides of the dado on each of the legs on both sides. Flipping it over in the case of the legs, not the horizontal brace, means it must be exactly centered on the width. The dado must be stopped the width of the cross brace in from the end as well. These mock-ups don't show that, they are just through cuts. 

A self centering router plate like a doweling jig comes to mind.

Anyway it's a entertaining challenge, for me at least. :laughing:


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## cabinetman

woodnthings said:


> I don't expect an answer or solution, but I'm probably gonna go a 3/4" stack instead of the flip method. I realize I'm makin' it more complicated than just one dado up and one down and interlock the boards, but I see this a somewhat stronger and resistant to racking.


If you don't expect an answer or solution, why post it? :laughing: Ask for comments and opinions. It's an interesting joint. My opinion is that without glue, if the pieces slide together without being smacked with a mallet, there will be axial stresses to allow some side movement, which will eventually wear out the fit. Unglued joints need some way to be drawn tight to eliminate movement.

Creating that might be easier to use one side guide reference for distance from that side, and use determined spacers for any width variation to the machining. JMO.












 







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## tcleve4911

Very cool Bill...
It looks like Japanese Joinery
Are you building this knockdown for the shop ?

Can't wait to see the self centering router guide that you're going to prototype....:yes:


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## woodnthings

*Japanese?*

I only wish I were that good! I do have a few books on thier joinery and I still don't understand how they do some of them...:blink:

Actually it was inspired by a request from the local Art Centrer which needs a simple space saving or collapsible table to be used with some donated glass shelves 12" x 72" for display. I told them I'd make a prototype/mock up and give them a quote for 3 or 4 units. Cost is a big factor as they are non-profit. I plan to use construction 2 x 12's and plane them to uniform thickness before machining the dados, to remove dimensional variations, twist, cup etc. It's still not an official job/contract, so I'm treating it as an interesting joint and possibly to be executed in 2 different hardwoods as a 3 board table. Also inspired by gus's beautiful table posted here a while back.  bill


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## woodnthings

*I can build that joint with 3 tools....*

OK. Build that joint!...an old TV show name that tune...
Actually without a router or a dado head in the table saw....I could even do it without a table saw, just a circ saw....:blink: Yah, sure.:no:
OK. Here's how: rip all your horizontal braces to 10".
Rip 2 leg braces to 12". cut the up and down dados so they interlock at right angles. Then fill in the *side pieces *on the horizontals and legs cutting them to fit exactly. BTW I used a table saw for ripping and a RAS for the crosscuts, just 'cause I could.
The side piece material need not be the same thickness or the same material as the core or middle. The core can be plywood or particle board or hardwood, the side fills can be whatever material you want on the finished piece. I used all 3/4 particle board 'cause that's what I had on hand for this mockup. 
 bill


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## mdntrdr

*That's Cheatin'!*

Great idea, that keeps the variables to a minimum. :thumbsup:

............................................... ....  :laughing:


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## aaronhl

Too confusing!!!! Great work!


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## kuroitaka

genius


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## Oneal-Woodworking

I want your tablesaw! 

LOL!


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## woodnthings

*which one?*



OnealWoodworking said:


> I want your tablesaw!
> 
> LOL!


:blink:


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