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plywood carcass construction dado depth

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9K views 21 replies 11 participants last post by  oldnovice 
#1 · (Edited by Moderator)
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
 
#5 ·
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.
 
#9 ·
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.
 
#11 ·
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.
 
#12 · (Edited by Moderator)
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
 
#18 ·
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
 
#21 · (Edited by Moderator)
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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