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Discussion Starter · #1 ·
I’m using ¾” plywood for my base of a cabinet with wheels. I’ve always been a little skeptical of dado's because I’m afraid of weakening the piece for horizontal stuff that has to support weight. I don’t have so much a problem going half the width with vertical pieces only horizontal. It looks better to go half the thickness, but I’m thinking about only 1/8” or maybe 3/16” on ¾” Plywood. Just enough to keep it in place :shifty:

What do you do?
 

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Old School
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I’m using ¾” plywood for my base of a cabinet with wheels. I’ve always been a little skeptical of dado's because I’m afraid of weakening the piece for horizontal stuff that has to support weight. I don’t have so much a problem going half the width with vertical pieces only horizontal. It looks better to go half the thickness, but I’m thinking about only 1/8” or maybe 3/16” on ¾” Plywood. Just enough to keep it in place :shifty:

What do you do?
On ¾" plywood I machine a ¼" deep dado.




.

 

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Discussion Starter · #3 · (Edited)
I actually have used ¼” on everything in the past, but I noticed that most of the store bought furniture I have around the house is about half the thickness and I don’t really know why unless it’s for looks.

:oops:Well I guess Not everything, I just noticed a hutch I built 30 years ago that has 1/8" dado's :laughing:
 

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I'm with ya!

On my recent plywood project, 3/8" into 3/4" plywood seemed too deep, like it might compromise the stiffness of the overall sheet. 1/4" seemed to shallow to hold the shelf. So, I made mine 5/16". I doubt it changed anything, but it sure made the calculations more fun!
 

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I set my router dado jig up to KEEP 1/2" thickness of my 3/4"+/- ply for dados. Measure down to the tip of the bit using a scrap of the same material. I prefer to take the "fun" out of my calculations... As much as I've tried, you can't cut a piece out of the middle and stick it on the end when it's too short!!! :laughing:

... I doubt it changed anything, but it sure made the calculations more fun!
 

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You will weaken the plywood unless the dado is completely filled. And just like mortises, the old rule is still "3rd and long". So in `3/4 plywood, 1/4" would be my depth.
Speaking of 3/4" plywood; it ain't! So in order to completely fill the void, you need to be able to cut an 'exact fit' dado. Here's a pic of one of mine, but there are plenty of simpler variations on-line. How it works is: you place the piece that's going into the dado between the fence guides, squeeze and tighten. Then rout first one way and then the other. Mine are self-clamping and self-aligning for speed of use. I also use them for sliding dovetails. Which, by the way, is my favorite dado!

 

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Discussion Starter · #10 · (Edited)
You will weaken the plywood unless the dado is completely filled. And just like mortises, the old rule is still "3rd and long". So in `3/4 plywood, 1/4" would be my depth.
Speaking of 3/4" plywood; it ain't! So in order to completely fill the void, you need to be able to cut an 'exact fit' dado. Here's a pic of one of mine, but there are plenty of simpler variations on-line. How it works is: you place the piece that's going into the dado between the fence guides, squeeze and tighten. Then rout first one way and then the other. Mine are self-clamping and self-aligning for speed of use. I also use them for sliding dovetails. Which, by the way, is my favorite dado!

Thanks, I really need to make one of those jigs. I've had one in my bucket list, but just never got around to it. I guess now would be as good a time as ever. Is there plans for one like you got someplace?

Update: I was just searching Google for a dado router jig and came across that exact same jig you have there at woodsmithshop http://www.woodsmithshop.com/download/204/adjustabledadojig.pdf.
So Thanks again
 

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Sleeper, I teach jig making classes and have had students build over 30 of that jig. Pay particular attention to the sliding clamp head. All of the parts in that assembly MUST be crafted exactly. Also, I have my students screw the hardboard fences to the fence rails instead of gluing. Makes replacing, if necessary, easy.
Get it right and you'll not only learn a lot, but you'll also love the jig!
 

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GeorgeC said:
If you glue the dado joint why is there ANY loss of strength.

George
You would have to be sure to get glue on all of the matting surfaces then the joint would be just as strong. If you just run a bead of glue in the bottom of the dado with little or no squeeze out then not as strong.
 

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Old Methane Gas Cloud
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Here ya go, JohnnyB!

No excuse now. :)
I was at a trade show many years ago. A vendor was giving away "square tu its". It was printed with something like, "Everybody has a bunch of round tu its. A square tu it is very rare."
 

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Old Methane Gas Cloud
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It really doesn't make much difference, 1/4, 5/16, 3/8, . . . . .

If you make the dado a snug fit for the plywood to be inserted and it is glued in place, the structural integrity is basically unchanged.
 
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Discussion Starter · #19 ·
I finally built a router dado jig. I used some stuff lying around, but I did not have any of the hard board that everybody seems to be using. I wanted it as long as I could and the 1/8” plywood I had was only long enough to cut two 31” pieces. I was doing it from memory and thought I had it right until I looked at the photo posted here again. :huh:

I made it to cut 1 ½” wide dados because I occasionally dado for 2x4s. Anyway I hope this is going to work.

 

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A good jig is one that works. A great jig is one that works every time! I'd think you have one there. 31" cut is good for base cabinets (24") as well as bookcases. I cut the dados for both sides of my bookcases, then rip the sides apart. They can't help but line up. Let us know how it works.
 
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