Dado Depth?,, added new question???

larry merlau

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Ok this is for research and the comparison of other woodworkers logic.. i have made many dados, and when i first started in this hobby i would use plans given me threw a magazine which told me to do this or that.. but now after a board or two has been ran threw the saw with a dado head installed.. i have had some of my own ideas..

so whats your most used depth of dado and why? for me on 3/4" stock it was always 3/8" deep but now i tend to go with a shallower depth of 1/4", reason being the shear strength is the same i believe in both depths and the shallower depth actually gives a stronger side piece..

now i got a dilema,, i have a side that is 26" wide and 68" long ,, that needs 5 dados the 26" way.. i thought i could use my dado blade but my head wasnt turned on fully.. how do i support it way out in no mans land to make the first dado that is up 12" from the end of the plank????
 
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I to am of the half the thickness club.:thumb: Not so much worried about the side strength as I am of the lip or to put it another way how much wood can I get under that shelf.
 
Half the thickness is to much. On 3/4" material I try to leave 1/2" of material. Makes the math much simpler and with plywood being less than 3/4 thick your dado is less than 1/4".

On 1/2" ply I leave 3/8" of material. Again the math is easier and it gives you more meat to nail/screw the pieces together.

The dado should only be thought of as an alignment aid. I've built many a cabinet in my 30 plus years of wood working without dados that has stood up just fine to daily use.

At work we use dados because for one the cnc cuts them and secondly it makes assembly of the cabinet a no brainer that a trained monkey could do.
 
About 50 years ago my shop teacher said dados are cut to 1/3 the thickness of the stock. That means on 3/4 stock you cut the dado 1/4 deep. It's worked well for me.
 
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When I use dadoes, I usually go half the thickness on 3/4" material. I'll do 1/8" or 3/16" on 1/2" material to leave a little more 'meat' for screws.
 
Count me in the 1/4 inch school. To me this allows dados on both sides without worry. This leaves slightly less than 1/2 inch on nominal 3/4 inch plywood (although more of the good plywood is now coming at 19 mm thick, which is a lot closer to 3/4 than 23/32.)
 
I dont think 1/4 inch or 3/8 inch depth really makes much of a difference as far as the sidewalls integrity.
For me, the measurements of the cabinet also sometimes dictate the depth.
(as in real careful planning, allowing 1/4 inch waste to trim, sometimes getting several lengths out of a sheet or a piece of a sheet I might make the dados smaller so I dont have to go to another sheet. Every inch counts when Im using veneered plywoods that run over 100 bucks a sheet)
Ive run into headaches when I need 4 shelves and find out Im 1/2 inch short, and have to buy a new sheet.
 
This has been very interesting. Strangely I have looked at a set of router table plans where a dado depth of only 7/32 was used. It was even noted that 1/4 wasn't used for the reason of compromising the overall size of the project. Compromising the size? It's a router table with only two joints in any direction.
I'm wondering would the number of plies influince the depth of dado in a plywood project?
 
This has been very interesting. Strangely I have looked at a set of router table plans where a dado depth of only 7/32 was used. It was even noted that 1/4 wasn't used for the reason of compromising the overall size of the project. Compromising the size? It's a router table with only two joints in any direction.
I'm wondering would the number of plies influince the depth of dado in a plywood project?

good point, guy? not sure but would think that would enter in to the equation,, in my case i am using solid wood so for the most part it wouldnt. but the construction needed and in plywood specifically the different depths have there merits.
 
At least two plies of plywood so I can be sure to get some glue on a cross grain.

Whatever looks good on solid wood. I'd generally go less than 1/2 because you don't usually need that much shoulder to hold and you're compromising the strength of the dado'd piece the deeper you make it. If its a thicker piece, I might go 1/3, thinner maybe 1/4, really thick or there is some aesthetic maybe 1/2.
 
If you think about it you are making a cut in wood then filling up the same cut with wood and glue. I don't think that you are compromising the strength of the wood at all by going halfway with a dado.

If it's a center piece, like Allen, I do a 1/4" dado on both sides. Other than that it's always half the thickness. Probably because that's the way I was taught and also because my dados aren't always perfectly flat in plywood. In solid wood I always use a router plane to even out the dados.
 
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