back to back dados

[Scott Welty]

Thanks for all the help on the desk design. Design has changed and now I have this question. Is it ok to form back to back dados? 1/4 deep each on a 3/4 plywood panel. See the sketch.

Thanks as usual,

Scott376190

[Bill Adamsen]

Lots of articles testing this if you google "dado depth on plywood" or something similar.

The "rules of thumb" I was taught were ...
1) leave at least 1/2 the material – so for back-to-back dados on 3/4" (one half is 3/8") that would suggest 3/16"
2) choose something that makes the math easy – why most choose 1/4"

I almost always use 3/16" even for single sided dados, certainly in a quality plywood like baltic birch or lumber core.

[glenn bradley]

I'm with Bill. I go a bit lean if I am running back to back.

[Martin Wasner]

I go an 1/8" deep leaving 1/2" of material when it's on both faces and in plane. My standard dado is 3/8", I'm just used to the math.

I'd also dado the mid deck instead of both sides of the partition.

[Jim Becker]

I'd go 1/8" deep, too, for 3/4" material for back to back grooves. You don't need a deep rebate or groove for a strong joint...the glue will do the work just nicely and the narrow shoulder of the groove you do cut will help support it more than you might at first think. The real benefit of the grooves, in addition to adding a little strength, is exact alignment and easier assembly. :)