# Newbie: Dado depth



## Double (Feb 17, 2010)

Cutting dados in 1/2 birch veneer ply for carcass of bookshelf using router table.

Is there a standard depth, like 1/3 thickness?


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## rayking49 (Nov 6, 2011)

In 3/4 I always dado half the thickness. If I make a tenon I make it 1/3 .


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## cabinetman (Jul 5, 2007)

Double said:


> Cutting dados in 1/2 birch veneer ply for carcass of bookshelf using router table.
> 
> Is there a standard depth, like 1/3 thickness?


I wouldn't use 1/2" for a cabinet carcass. I would use 3/4", and dado/rabbet depths of 1/4" is more than adequate. If you have to use 1/2", I wouldn't dado more than 1/8", and IMO, you'll still have a fairly weak panel.












 







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## Double (Feb 17, 2010)

Well I'm stuck with 1/2 for this set but depending on howe it turns out I may go to 3/4 for the larger set in the guest bedroom.


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## Jim Moe (Sep 18, 2011)

I always measure plywood I purchase first with either caliper or micrometer as it varies so much in thickness. Then set your dado's either 1/2 or 1/3 of that thickness. The last 3/4" Birch ply I purchase measured out to 11/16".


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## Double (Feb 17, 2010)

I noticed the same thing, the ply I picked up at Woodcraft measures right on 1/2 while the same ply at Lowes measured just above 3/8


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## BassBlaster (Nov 21, 2010)

Double said:


> I noticed the same thing, the ply I picked up at Woodcraft measures right on 1/2 while the same ply at Lowes measured just above 3/8


 Thats because ply sold at the big box retailers is sold in 32nds thicknesses.

Not sure how many cabinets your building but I would be looking for a hardwood retailer in your area. Woodcraft is WAY overpriced on many things in thier store, especially plywood. I try not to buy any material there because it is so overpriced. I have been buying some turning blanks there recently but only because its the only place local to me to get turning blanks but even then, I get them out of the bargain bin.


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## cabinetman (Jul 5, 2007)

A 1/2" substrate IMO makes for a poor substrate for carcasses. Once a dado or rabbet is machined, there's not much substrate left to carry the joint. Granted, with a back rabbeted in and a face frame, it will seem fairly stout. 

You also don't have much substrate to hold screws. Baltic Birch or Apple Ply would be the best of substrates, but I still wouldn't use them. As a minimum I would use 5/8" either in plywood, MDF, or Melamine.












 







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## jraksdhs (Oct 19, 2008)

*Imo*

I personally use 3/4" for all cabinet construction, even backs. Some call that over kill, but its an easy sell to customers. On the subject of 1/2" for sides, if you cut a 1/4" depth dado to receive a 1/2" bottom or something, once glued and screwed that side is just as strong as it was before. Im not sure if your planning to park cars or jump up and down on your counters but Id say your fine. Before I started using 3/4" i only used 1/2" and never had a problem. But then again, this just my opinion. 

jraks


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## Double (Feb 17, 2010)

I'm going ahead with 1/2" for these shelf units, they are only 36" height and won't be supporting that much weight, but from what I've read here I will definitely transition to 3/4" for the next project, which will need more support.


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## Big Stud (Dec 2, 2011)

One of the reasons most people use 3/4 as opposed to a lesser thickness is the shelves will bow down in the middle over time, as well as the obvious strength difference when dadoing something less than 3/4. So if you have to do it with 1/2", either don't dado the shelves, or as mentioned, only dado 1/8" or slightly more. Also use a stiffener under the shelves to help support them. 3/4 x 3/4 would be a min stick size that I would use. In this case, bigger really IS better, :thumbsup:


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## Double (Feb 17, 2010)

I can tell after assembling the first booskelf that bowing would be an issue in the future. The largest shelf, which is on the bottom sits 3" above the floor so I can trim it out.

I'm definitely going to reinforce it from underneath before installing in order to prevent flex. As for the upper shelves, which will do lighter duty, I may add some face framing in order to stiffen them, but they are also getting a 1/4" backing on each unit.

*On a side note*, do you guys typically vave to make a second pass with the router in order to get the full width of the dado?

In other words, with a 1/2" bit (The plywood is right on 1/2"), after the initial pass, even after cleanup sanding, the fit of the dado is extremely tight, but with a light second pass where i can hear the bit still lightly trimming, the fit is a nice snap it that seems right on.

If it works why worry about it, but it seems to fly in the face of logic that the same bit on the same track with widen the cut. Am I crazy?


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## jlord (Feb 1, 2010)

Double said:


> I can tell after assembling the first booskelf that bowing would be an issue in the future. The largest shelf, which is on the bottom sits 3" above the floor so I can trim it out.
> 
> I'm definitely going to reinforce it from underneath before installing in order to prevent flex. As for the upper shelves, which will do lighter duty, I may add some face framing in order to stiffen them, but they are also getting a 1/4" backing on each unit.
> 
> ...


I would add some solid wood edging to the front of your shelves. It would help add stiffness to the shelves. It would also make the shelves look thicker than they really are. I use nothing less than 3/4" ply for the shelf unless it's a small project.


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## jschaben (Apr 1, 2010)

Double said:


> I can tell after assembling the first booskelf that bowing would be an issue in the future. The largest shelf, which is on the bottom sits 3" above the floor so I can trim it out.
> 
> I'm definitely going to reinforce it from underneath before installing in order to prevent flex. As for the upper shelves, which will do lighter duty, I may add some face framing in order to stiffen them, but they are also getting a 1/4" backing on each unit.
> 
> ...


Sounds like this little tool would be handy for you right now. It will estimate the amount of sag on a shelf given shelf length, material, expected loads, edge banding, etc...
http://www.woodbin.com/calcs/sagulator.htm


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## Double (Feb 17, 2010)

That's a huge help, nice tool.

So it looks like my best bet is to add a center divider for each shelf, that would reduce the span to about 18".

I may add a face frame as well, but it would require almost a 1" by 1/2" lipping to reduce sag enough.


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