Weight Bearing Shelves

[Jan Bianchi]

I am making a cherry Shaker hutch that is detailed in Fine Woodworking Jan-Feb. 2007. I have asked several questions about it in the past from this community and have always received very helpful replies. I am attaching a picture of the lower cabinet which is finished and "in service".

My upper cabinet is different from the article's in that my version's upper shelves will be 15 inches deep rather than the 9 3/4, still 44 inches long and 3/4 thick. The shelves will be attached to the solid wood sides by tapered sliding dovetails ending in face frame. I am concerned about the shelves sagging. The upper part of the article's cabinet was designed for display, not storage. Do you think I will need stiffeners under the shelves to keep them from sagging?

I don't want to do that because they will show below the muntins in the glass doors. I have been using my great grandmother's walnut china cabinet as a model. It's 40" x 15" by 3/4" shelves are attached to the sides by cleats. They do not sag when fully loaded with china and glassware. While I could put stiffeners only below the lower shelf and store only light items on the top two shelves, I'd rather not.

I have checked the sagulator calculator online, assuming 10 lb load per foot (ten large plates being 6 lbs). It says that creates a visual sag of .003 which is not visually noticeable and is acceptable. I have to decide this now since I won't be able to add stiffeners after this is assembled. Doesn't the additional depth of the shelf mean less potential for sag, not more?

[David Eisenhauer]

Will the back of the shelves be attached to the cabinet back? Can You add a "stiffener" to the front of the 3/4" shelves (1"?, 1-1/8"?, 1-1/4" wide?) without affecting the look? In my experience, anything over 36" long for a 3/4" shelf may cause problems if the shelf load is not a known, controlled load. The plates aren't too bad, so it will probably be OK. I turn out bookcases from time to time, books get heavy quick, so perhaps I am overly gun shy about unsupported shelf lengths. The "display" style cabinets I turn out do allow me to attach the back of the shelf to the back of the case and I believe that helps a bunch.

[Jan Bianchi]

Will the back of the shelves be attached to the cabinet back? Can You add a "stiffener" to the front of the 3/4" shelves (1"?, 1-1/8"?, 1-1/4" wide?) without affecting the look? In my experience, anything over 36" long for a 3/4" shelf may cause problems if the shelf load is not a known, controlled load. The plates aren't too bad, so it will probably be OK. I turn out bookcases from time to time, books get heavy quick, so perhaps I am overly gun shy about unsupported shelf lengths. The "display" style cabinets I turn out do allow me to attach the back of the shelf to the back of the case and I believe that helps a bunch.

I probably can't attach the shelves to the back. The back is a large framed panel of 1/2"shiplapped or T&G cherry. I'd have to go through the 1/2" material which doesn't sound good to me. Any lip under the front of the shelf will show since the muntins are only 3/4" high.

[Jim Matthews]

Make the shelves from a quality plywood with lots of layers
and trim out the front with solid wood.

Plywood is amazingly stiff across a span this size.

[Guy Belleman]

A couple stacks of plates can get real heavy, especially over a 44" span. My experience is that any span over 30" will sag over time, even plywood, without some rigidity built into the shelf or cabinet. Also, depends on your vision of how long the cabinet may be used. Rigidity can be built into the cabinet frame, which will reduce the amount the interior shelf can deflect. Flexing, or sag, on a shelf in a cabinet means that the rest of the cabinet has also flexed, or twisted, some too. If you make the top and bottom very rigid, and your sliding dovetails are tight, then the interior shelf can't really flex, or sag. With your wider shelf, I think you might look at doubling up the top and bottom part of the case, or at least reinforcing them in some manner.

[Richard Wagner]

Why not build in some rigidity and quit worrying about it.

[Andrew Pitonyak]

I built a very large desk with a hutch. The hutch has two very large shelves. I used shelf pins so that the shelf is adjustable in height. I included two shelf pins along the back so that the shelf has some support on the back as well as the sides. You could do something similar. Since the shelf will be set in place, you could attach a small support piece of wood attached near the center along the back.

The next question becomes, how thick can you make the wood? Thicker is probably better.

[James Hansen]

When I make ply shelves, I use 1 1/4" X 3/4 end caps on the front and back with what ever material the rest of the project was made with. This not only makes them very strong, but gives it a nice looking decoritive cap.

[Wade Lippman]

I probably can't attach the shelves to the back. The back is a large framed panel of 1/2"shiplapped or T&G cherry. I'd have to go through the 1/2" material which doesn't sound good to me. Any lip under the front of the shelf will show since the muntins are only 3/4" high.

I don't follow you. Why is going though 1/2" material not good?

[Doug Garson]

I built a very large desk with a hutch. The hutch has two very large shelves. I used shelf pins so that the shelf is adjustable in height. I included two shelf pins along the back so that the shelf has some support on the back as well as the sides. You could do something similar. Since the shelf will be set in place, you could attach a small support piece of wood attached near the center along the back.

Just a thought, but if you support the shelf on pins as suggested and finish the shelf top and bottom so that it is reversible. If it starts to sag you could periodically flip it over to take the sag out. In a worst case scenario, if it sagged too much it could be replaced since it is not glued in.

[Jan Bianchi]

One-half inch thickness just doesn't seem like enough bulk to really help hold up a shelf. I may be wrong about that.

I can't use pins to hold up the shelves from the sides. The sliding dovetails are what keep the sides parallel and rigid. There is no "bottom" to the upper half of the hutch. It just sits in a groove along the back of the lower part of the hutch. I could put pins in the back. As much as possible I am trying to stay with woodworking techniques that would have been used by the Shakers.

The muntins in the glass doors are only 3/4 high so any shelf thicker than that will show. Not a disaster, but not the design either.

[David Eisenhauer]

I use 1/4" plywood cabinet backs to hold up my shelves. I am not up on all the Shaker habits, but how about a 1/4" - 3/8" dowel through the center (to minimize the effect of wood movement) of a vertical back panel board and into the shelf back every now and again?

[Sam Murdoch]

I don't want to do that because they will show below the muntins in the glass doors. I have been using my great grandmother's walnut china cabinet as a model. It's 40" x 15" by 3/4" shelves are attached to the sides by cleats. They do not sag when fully loaded with china and glassware. While I could put stiffeners only below the lower shelf and store only light items on the top two shelves, I'd rather not.

I have checked the sagulator calculator online, assuming 10 lb load per foot (ten large plates being 6 lbs). It says that creates a visual sag of .003 which is not visually noticeable and is acceptable. I have to decide this now since I won't be able to add stiffeners after this is assembled. Doesn't the additional depth of the shelf mean less potential for sag, not more?

While I would bet against this your Grandmother's cabinet is proof that I would be wrong - though you are adding 4" to the length . My general rule for shelving, other than linen shelves, is no more than 3' span for 3/4" material (ply or solid) without added support. Making the shelves 7/8" or 1" thick would certainly add to the stiffness - your call as to how much that would change the esthetics.

Another solution would be to add a vertical support in the center. It would be hidden by the center stiles. Might need to be let into the shelves in order to place it properly within the depth of the cabinet, or make the shelves a bit less deep.

[Peter Quinn]

I'd go with a 1" solid shelf, or at least 15/16"' and taper the first few back on the bottom side like a raised panel, so I'd fades to the back, but shows 3/4" at the leading edge for the visual. Or dovetail in a support post that sits behind the stiles on the doors, doesn't have to be too wide, maybe 1" to 1 1/4", holds up the shelves in an inconspicuous way. Loading a 40+ inch 3/4" shelf with granny's china sounds like a problem to me....unless you use jatoba for the shelves, or glue a strip of cherry to a stronger species so you get the cherry nose, intensely strong back. And definitely use the back as a support, 1/2" solid paneled back will add great support.

[Frank Drew]

The next question becomes, how thick can you make the wood? Thicker is probably better.

I agree, both in terms of stiffness and also, past a certain length, appearance; 3/4" can look a bit dinky as a shelf gets longer; why not try 4/4, or even 5/4?

If you totally object to thicker "looking" material, you could use 4/- or 5/4 but bevel the underside of the shelves' front edges, leaving a 3/4 show edge for the look you want but with added strength (the bevel should be rather wide so that the true thickness of the shelf doesn't show to the casual observer.)