How much dado? is enough?

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Folks --
I was planning on making some utility storage towers out here, and the question cam out - how much kerf is enough?
The towers are 6 foot tall 3/4 plywood, each "chamber" about 18 inches square. The sections that divide it up were to be set into some dado cuts in the sides and back ( about half of 3/4 in ). glue and some wood screws were to hold the assembly together. The unit is not destined for high mass items. More like a general sort box for light to medium goods as the battle of entropy in my household moves to different rooms. Some bracing may be in the picture for the shelves.
Once I finished this plan in sketchup, the reviewed it for reasonableness ( habit from software engineering ). The question that came up was -- how deep do you need to make a dado slot so it works as support?
Thanks for your replies!
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wrote:

In 3/4" ply, I usually go 3/8" deep.
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dado dado
Daylight come and me wanna go Day me say day me say day Me say day me say dado Daylight come and me wanna gohome work all night and a drink a rum (daylight come and me wanna go home) Stack banana till the mornin come (daylight come and me wanna go home) Come mister tally man tally me bananas (daylight come and me wanna go home) come mister tally man tally me bananas (daylight come and me wanna go home) lift six foot seven foot eight foot bunch! (daylight come and me wanna go home) six foot seven foot eight foot bunch! (daylight come and me wanna go home) day me say dado (daylight come and me wanna go home) Day me say day me say day me say dado(daylight come and me wanna go home) A beauitful bunch of ripe banana! (daylight come and me wanna go home) hide the deadly black tarantula! (daylight come and me wanna go home) lift six foot seven foot eight foot bunch! (daylight come and me wanna go home) six foot seven foot eight foot bunch! (daylight come and me wanna go home) Day me say dado (daylight come and me wanna go home) Day me say day me say day me say dado(daylight come and me wanna go home) come mister tally man tally me banana (daylight come and me wanna go home) come mister tally man tally me banana (daylight come and me wanna go home) dado dado(daylight come and me wanna go home) day me say day me say day me say dado (daylight come and me wanna go home)
....one of those days...
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wrote:
You've got a really sick mind, Robo.. I wanna be you if I grow up!

mac
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I kinda screwed myself with that one, the damn song is stuck in my head. Is it in yours? If it is, then:
http://i123.photobucket.com/albums/o290/Robatoy/rflol_seal1.jpg
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wrote:

Nope... it was but I fixed it!
We do karaoke, and sometimes I couldn't sleep that night because a song was running in my head.. She taught me a cool trick.. The song runs like that until you FINISH it.. Just sing or think the song until the end and it really does go away.. kind of like you've reached the end of a tape and it stops spooling..
mac
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"Robatoy" wrote

Things a little slow up there in the frozen north?
Max
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LOL
I wish. Angela's 41st birfday, prepping a shipment for Toronto for Monday's installation, main guy wanted a day off up to me arse in work.
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80 F here today.
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BETTLEJUICE!
BETTLEJUICE!
BETTLEJUICE!
SHOWTIME!
Dave in [Floresville] Texas
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Catherine O'Hara, who plays the mom and breaks into that song, is funny all the time in real life. I had the pleasure of experiencing that first-hand at a fund raiser.
I think Michael Keaton is some funny guy in Johnny Dangerously.
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I use a minimum of about 1/8 of an inch in hardwood and 1/4 inch in plywood and mdf. You can go deeper if you want.
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I've always used 1/3 of total thickness as my benchmark for a dado. So with 3/4" plywood, I'd dado 1/4" for shelving. The only thing that would make that depth insufficient is if the shelves sagged enough for it to pull out of the dado.
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Save yourself a little grief.
Don't start doing a full width dado that is a pain in the wazoo to ever get correct.
Use a smaller rabbet joint.
Cut the dado with a "known" width.. like 1/2" using a dado stack or a router bit.
I like 3/8" deep but a 1/4" will do nicely.
Now just trim your rabbet slowly until you get a perfect fit.
Practice this a couple of times and you will not attempt to get a "odd size" piece of plywood fit a perfect cut 3/4" dado.
Dan wrote:

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Pat Barber wrote: ...

...
And if the shelving is ply rather than solid material as I gather it is, put the rabbet on the bottom so the weight of the stuff on the shelf doesn't tend to cause split-out or delamination.
For light duty applications, aethestically more pleasing to do other way as it's a cleaner-looking joint if the shelf disappears into the dado, but a shop storage unit may carry a pretty good load and durability trumps in that case...
imo, etc., ...
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When I use this method, I put the rabbet on the top side of the shelf .. .. keeps the weight of the load from pulling the plies apart.

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<<<__ Bb __>>> wrote:

That's backwards -- the load in the center is pushing down on the lower plies creating tension load at the bottom. Other way up, the center is resting on the lower plies.
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Doing it your way, a heavy load could separate the plies at the edges where the rabbet ends. The sides of the rabbet are not supported .. only the tongue .. this is where separation is most likely.
dpb wrote:

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<<<__ Bb __>>> wrote:

I think you're backwards, still -- when the rabbet is at the top, the load causes a deflection downward which introduces tension on the end.
When the rabbet is on the bottom, the support is on the bottom and the bending load is compressive.
Sorry I brought it up, I guess... :)
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> dpb wrote:
>> <<<__ Bb __>>> wrote:
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I was on your side until he explained it a second time and something in my head clicked. If the rabbet is on the top, then the tongue is on the bottom. I kept misreading "rabbet" as "tongue," or at least misenvisioning it.
Full plys on the bottom, shortened plys on the top.
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