# plywood carcass construction dado depth



## Belg1960 (Jan 3, 2010)

Guys this is something basic but what depth do most people use when making dados for horizontal shelves/dividers into 3/4 vertical plywood? Thanks Pat


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## bluekingfisher (Mar 30, 2010)

Pat, usually about half the thickness of the material, therefore 3/8" although 1/4" is suitable for some projects.

I wouldn't however exceed half the thickness


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## bondogaposis (Dec 18, 2011)

I go 1/4".


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## ClayandNancy (Feb 22, 2010)

What if you have two dadoes on opposite sides at the same spot? Is 1/4" ok or too much?


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## SamuraiSaw (Jan 8, 2013)

Agreed on not exceeding half the thickness. A lot depends on the span of the shelf, if there is a back to the cabinet, and the fastening mechanism of the shelf. If you will be using screws to hold the shelf in place or if you will be able to attach the back to the shelf a 1/4 dado will be sufficient. All you're doing is registering the shelf to the side. If the sides are visible you'll want to go deeper to provide more stability.


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## Cosmicsniper (Oct 2, 2009)

I normally do 3/8", but beware that 3/4" plywood is not necessarily 3/4" .


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## Cosmicsniper (Oct 2, 2009)

@ClayandNancy - I would use a 3/16" dado in that situation, likely also mounting it in a face frame or edge banding.


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## JesseTutt (Aug 15, 2012)

I tend to use about 1/4 to 1/3 the thickness of the material, so I would normally use 1/4 dado on 3/4 plywood. I would use less if I had a dado at the same location on the opposite side.


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## Gene01 (Jan 5, 2009)

As SamuraiSaw said, it depends on the application. However, with today's glues, 1/4" is sufficient for MOST applications. It's the span and prospective weight on the shelf that deserve consideration. The actual joint will be strong and solid.


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## Cosmicsniper (Oct 2, 2009)

@Gene - I'm trying to think when you'd even need glue (from a structural standpoint), especially if there's a face frame and cabinet back to lock it in? To me, I often just glue it in to make sure it doesn't shift around and rattle over time.


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## SamuraiSaw (Jan 8, 2013)

I always glue shelves/partitions in place to provide additional stability. I've never had a customer complain because I over-engineered a piece, but I have certainly regretted the opposite when (and invariably it will) a joint fails and I have to repair it.


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## Belg1960 (Jan 3, 2010)

The span on the two units is only 20" and it will have a back of either 1/4 or 1/2 material probably luan ply. 
Another thought I'm using unfinished ply to build these but decent quality material, to hand finish it would most of you assemble first, or prefinish large sections and then machine them? And assemble after?
For the smaller cabinet like this I think the 1/4" will do, for the dado. Never thought about the situation where 2 dados would be at the same height but not in this case. Thanks much


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## SamuraiSaw (Jan 8, 2013)

If it is stain grade, I tend to machine the parts, apply stain, then assemble and top coat. That helps prevent problems with glue interfering with the stain. If paint grade, do the complete assembly then finish.


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## Cosmicsniper (Oct 2, 2009)

@Samurai - I'm not suggesting that you could always leave this joint unglued. I wouldn't. I was thinking more in terms of a shelf/divider (see OP) as opposed to the cabinet box itself. I should have clarified that.


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## SamuraiSaw (Jan 8, 2013)

Cosmic, I tend to over-engineer stuff. My theory is if you can't park a car on it, beef it up!!!


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## bondogaposis (Dec 18, 2011)

What if you have two dadoes on opposite sides at the same spot? Is 1/4" ok or too much?

In that case I'd go 1/8".


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## Cosmicsniper (Oct 2, 2009)

I hear you, SS.


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## LeeBarker (Aug 6, 2010)

Industry standard is 1/3 the thickness of the vertical material. That holds true for dadoes both sides. There's no structural concern here because the load is down, not lateral.

The compelling reason to keep them the same is that the math stays constant; therefore, the machine settings and the shelf adds do not vary. This can be critical to consistency and quality.

Kindly,

Lee


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## ClayandNancy (Feb 22, 2010)

*Samurai and Bondo* Thanks there will be a face frame and a 1/4" or 1/2" back. Sorry *Belg1960* for hijacking your post. As for normal dadoes in ply I go 1/2 the thickness, glued and sometimes I use brads just to help hold until the glue dries.


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## Belg1960 (Jan 3, 2010)

Thanks for the input guys, all the info was taken in for future projects.


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## BinghamtonEd (Nov 30, 2011)

I'm in the process of building a kitchen island for my wife, and just glued/screwed the cabinet box together yesterday. The box has the bottom and one shelf. Sides and horizontal pieces were made out of 3/4" ply, with dadoes 3/8" deep. Back was 1/2", with 1/4" dadoes for the horizontal pieces. Strips of 3/4" pocket-screwed across the top to fasten the top to. Bottom shelf also is screwed in from outside of cabinet through the dadoes (to be covered in trim later). Overdone? Maybe. But when it came time to assemble the whole thing, it all came together rock solid and square. I should also note that this is a mobile island with a butcher-block top, so it will be going through slightly more stress than some other basic cabinets might.

On a side note, like others have said, measure your plywood first. I bought plywood listed as 23/32, used a 23/32 dado bit and come to find out, nothing fit, because the plywood was actually 3/4". Rather than re-route all of my dadoes on the sides and back, I just used the dado bit to cut a 1/32" rabbet on the undersides of the bottom and shelf to bring the mating thickness down to 23/32.


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## oldnovice (Mar 7, 2009)

*I agree with Lee. Simplicity and consistency!*


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