Booksehlf unit: Domino or dado?

Re: Booksehlf unit: Domino or dado?

Bill Tindall, E.Tn.

A piece of wood stick into a dado provides puny racking resistance. When I make a tall book case without a back I put a small shoulder on the shelf, like a half tenon. It is remarkable how much racking resistance this shoulder provides.

No doubt the Domino will be faster if you are experienced using it. Shelves will not be able to carry near as much load, if that feature is important. You won't shear a Domino but the wood in the shelf will fail under sufficient load.

Re: Booksehlf unit: Domino or dado?

Jim Dillon

Henry, while I am a BIG user of Dominos, I agree with Bill that a tenon with a shoulder (on the top side, i.e. an off-set tenon) would provide resistance to racking and still be strong enough to accommodate downward loading. My two cents. Jim

Re: Booksehlf unit: Domino or dado?

David Yoho

You might consider joining your shelves to the case sides a little different than going with a straight dado. Perhaps this idea is what Bill is alluding to, but since you're using 3/4" ply it's easy to cut a 3/8" dado in the sides and a 3/8" rabbet on the ends of the shelves. The shoulder from the rabbets will add strength and make cutting the joints less fussy.

A presumption...

Jim Matthews

If the sides are affixed at three points (Top, Middle and Bottom) is that sufficient?

Further, if the bookcase is fixed to a wall with a French cleat, even accidentally contact should be managed.

If a plywood back is installed, it should be very stiff.

Re: Booksehlf unit: Domino or dado?

David Weaver

I'd use dado and glue the shelves. I guess it's not trivial to get the dado in the back , though I did all of my kitchen cabinets that way with glue. No sag on half inch ply no matter what goes in them.

The key to making construction quick is having the space to lay all of the ply out for three sides and then pinning it together so that you can cut the dado with a router or dado plane. I'm going to guess that on this side of the forum, the former would be the way.

It was a lot of working on the floor to do things that way.

Re: Booksehlf unit: Domino or dado?

John McGaw

Others have brought up the factor of racking. That really depends on another part of the design: will the unit have a back or not? If it has a back, racking should never be a problem. I've only ever built a single unit without a back and, despite the shelves being held in place by through wedged tenons which are tremendously strong, each shelf has a lip about 1-1/4" high sticking up at the rear both to work against racking and to keep items from being shoved out the back.

Thanks - units will have a back

Henry (Raleigh NC)

Thanks all - there's goes my justification for a Domino...I expected these answers that dadoes were the superior construction.

I am not particularly concerned about racking; there will be a back on each unit, and as a wall-to-wall built-in, this will be fixed to the wall Racking is of course an element to always be considered, especially for shelving units.

Henry

Couple things

Ellis Walentine

I'm not sure why you want the shelves to be fixed, but that's another question.

You didn't mention whether these units will have backs or be built in, as opposed to free-standing. If both are the case, dados are fine, assuming you have enough room to cross cut them on your tablesaw. Faster yet, and likely my choice in this situation, would be biscuit joints, which are still fairly standard in the case-goods construction business. (I also like the look of shelves butting against uprights instead of being cut into them.) Dominos are loose tenons, which are fine for all kinds of joinery, but not necessary in this case.

Also worth noting is that a 46" wide plywood shelf will require substantial support along the front and back edges to prevent unacceptable deflection.

My 2¢

Ellis

and use a stopped dado

Bill Tindall, E.Tn.

If you are not going to face the front, stop the dado so the dado does not show on the front face

Re: Couple answers

Henry (Raleigh NC)

Ellis: I did not give the entire scenario, but here goes.

Fixed shelves were chosen because LED illumination is desired. I saw no way to allow movable shelves AND have LED strips on the underside of each shelf.

Units are built-in, wall-to-wall, and will have a back. Racking will not be an issue.

Interesting that you suggest biscuits as an option for shelf to case-side joinery. I would not have considered this (I actual have neither a Domino nor a biscuit joiner).

Shelf sag is a concern; shelves will be faced with a 0.75 x 1" tall (or maybe 1.25 piece. These are supports and to hide the LED strip lights under each shelf.

Henry

Face-frame construction, with LED strips

Henry (Raleigh NC)

Shelves will be faced with a substantial strip to assist with sag prevention, as wellas to hide LED lighting strips under each shelf.

Face of the units will have face frames - with upright pieces wide enough to tuck a wire in behind.

Henry

Re: Couple answers

John Foster

For nearly forty years I have made shelves, cupboards and bookcases with much the same design.

-3/4" plywood ( friends don't let friends do MDF )

-Dado the sides for the shelves 3/8" deep.

-Dado the back 3/8" deep for the shelves, make the back full width, rabat the back edges 3/8" deep by 3/4" width of sides .

-It helps to do each dado on the back and a double width side panel during the same table saw/router setup, then rip the side panel in half, all your shelf dados should be at the same spacing.

- Get several friends over and tell them to bring all the pipe clamps they have. Glue all the dados and Clamp up in one session.

- Fasten a strip of hardwood to the shelf fronts, extending upwards if you don't want stuff to roll off, extending downward if you want a flush top surface on the shelf.

- you now have one ugly piece of furniture, load it up with anvils as it is or put a face frame, edge banding, paint etc.. to make it presentable.

How thick is the back?

Henry (Raleigh NC)

Thanks John.

If you dadoed the back for shelves, how thick a piece do you use for the back?

Henry

Re: How thick is the back?

John Foster

3/4" too

3/4" back seems extreme

Bill Tindall, E.Tn.

I have never installed more than 1/4" plywood backs

A 4' wide shelf unit strikes me as gaping. Consider vertically dividing some of the shelves to make it more visually interesting.

For example:

Biscuits

John in NM

While I'm generally not wild about biscuits, I have to admit that this is one of the better uses I found for them. Biscuit joiners are generally flat on the bottom of the cutter shroud, and you can clamp a fence for each shelf (at the necessary offset between the blade and the outside of the tool) quickly cut several biscuit slots in the side. It works really well and is quick.

They also excel for face frames as I recall - pocket screw & glue the frame together, use biscuits as registration to the plywood or MDF case. Quick to build and tough.

Re: 3/4" back seems extreme

Henry (Raleigh NC)

Bill -

Agree that 3/4" back is more than needed. I'm unlikely to go that route. Fixed shelves at least allow gluing and nailing shelves along the back.

I appreciate the design aspects, but as described earlier - these are not individual units.

"... make a 3-unit built-in, with lower cabinets and upper shelving (fixed shelves)."

" ... 3/4 plywood construction, with a face-frame."

" ... 12" wide x 42-46" long shelf? Shelving units are part of a 3-unit wall-to-wall built-in."

Client has chosen 3 unit design, rather than 4 units, for the 11' span.... meaning 42-46" shelves or thereabouts.

Henry