How deep do you cut dados in 3/4 plywood

[Travis]

I am just about ready to start my first cabinet/built-in project. I plan to use dados and was wondering how deep you cut them in 3/4 shop grade red oak. I ran some test samples with 3/16, 1/4 and 3/8 and the 1/4 looks good but I have no experience to help base my decision.

PS.

Have digital camera and will start publishing pictures of the project as I progress for constructive criticism.

[jeff...]

I would think 1/2 the thickness of the material used or 3/8" in this case. But not so tight that there is no room for glue either.

[Monty]

1/4", 3/8" - I don't think it matters much, just pick something that makes the math easy!

[tom hintz]

I generally cut dados 1/3 the thickness of the piece they are being cut into.
However, another way to do it that comes in handy if you have to figure the length of the cross pieces (like shelves) is to cut the dados so 1/2" of material thickness remains. That way your cross pieces are an even 1" less than the width of the assembled unit.

[Ray Martin]

I would tend to agree with the idea of making the math easy. One of my favorite mistakes is to add the depth of one of the dados to the width of the shelf (yeah, it should be two times that depth since there is a dado on both ends of the shelf ). I would also suggest that you draw the project up with all the math on the drawing. That helps catch the mistakes that I'm so fond of making.

In building codes, there are limits to how much material can be cut out of a supporting member like a floor joist or a wall stud. The idea is to maintain structural integrity. I'm not sure where the rules for furniture making are but I tend to think you should leave at least half the thickness of the material that gets the dado. In other words, if you plow a dado in 1/2" stock, the dado should not be deeper than 1/4".

Ray

[McRabbet]

Travis,

For plywood carcass joints (the basic box for the cabinet), I generally use a 3/8" depth in 3/4" material. If the plywood is under sized, I make sure I leave 3/8" of material thickness for strength. If I'm working with 1/2" material, then I use 1/4" depth. I also recess 1/4" cabinet backs in a rabbet (actually a McRabbet in my case) set in all four sides of the back. Intermediate shelves or partitions are cut shorter to just meet the back panel. Where I attach face frames to the front of the cabinet, I leave the top and bottom 1/4" short of the cabinet sides and cut a 1/4" deep dado on the back side of the face frame to accept the sides -- this insures a square fit of the face frame to the cabinet. Attach the top and bottom of the cabinet to the face frame with pocket screws that won't be seen on the inside of the cabinet.

Rob

[Travis]

Thanks for the input. Rob, I really like your suggestion of leaving the cross members short and I am still LOL about McRabbets.

[DaveD]

I stick to 1/4" on 3/4" material. That's just me though. I like lots of 'meat' in the board I'm dadoing.

If you cut the dados too deep and they are too tight (yet you can force the other piece in the dado) you will find that the piece with the tight dados will start to arch away from the side with the dados. You then no longer have a straight piece.

Dados in things like particle board (or whatever that junk is called, the name escapes me) ) will make that point very weak and easy to break/crack if the dado is too deep.

Remember when you make the dados to measure the board you are trying to match. Seems 90% of 1/4" plywood isn't 1/4" any more.

[Splinter]

Originally Posted by McRabbet

Where I attach face frames to the front of the cabinet, I leave the top and bottom 1/4" short of the cabinet sides and cut a 1/4" deep dado on the back side of the face frame to accept the sides -- this insures a square fit of the face frame to the cabinet.
Rob

Rob,

Could you explain this again? Or have a photo...I'm having trouble getting an image of this in my head. I'm a little slow today.

Thanks,

[DaveO]

I think what Rob is saying is that when he makes the carcass of a cabinet that is 23½" deep (not figuring the face frame). The sides are 23½" and the top and bottom are recessed a ¼" (23¼"). Then a dado is cut in the face frame stiles (vertical members) a ¼", but not in the rails. The dado fits on the protruding sides and fits flush to the top and bottom. In case the carcass is out of square the face frame would still be firmly anchored but could accommodate the out of square carcass.
Does that make more sense, and Rob, am I even close to what you where thinking???

Dave

[D L Ames]

Dolan,
I believe what Rob as describing is how he attached the cabinet sided to his face frames. Make your face frames first then cut a 1/4" deep dado the same thickness of your cabinet sides. The placement of this dado is 1/4" in from the edge from the outside edge of your face frame so once your cabinet is completed you will have a 1/4" ear on either side of your cabinet. Like Rob mentioned, placing the sides into the dado helps to square up your cabinet as you assemble it. Also, there is an added benefit to the 1/4" ear on either side of the cabinet. If your placing a long run of cabinets in and you find that your measurements were off or the walls are not plumb then you can use a belt sander to remove some or all of the ears and gain 1/2" per cabinet. If you are dealing with a long run of cabinets you can quickly make up a couple of inches by sanding the ears off.

Clear as mud now...........right?

D L

[DaveO]

Well, now I am very curious to hear what Rob thought he was saying. Both interpertations sound like sound ideas.

Dave

[McRabbet]

DaveO and DL did a much better job of describing what I meant -- both said it very succinctly -- and this does insure that both the face frame and the carcass are square. One added point. For upper cabinets, I align the inside face of the carcass bottom with the inner edge of the bottom rail of the face frame so that they are flush with each other -- no lip to snag against.

Rob