Sag shouldn't be a significant issue with the shelf in question. It's
going to be supported presumably at each stud, so the span is at
Are you saying that a 1.5" thick torsion box would have 2/3 less
deflection than a similar length and THICKNESS oak board? (If so, why
is this true? I would expect it to be somewhat weaker than a solid
piece of the same dimensions.) An inch and a half is too thick for
this shelf. It would look ungainly. As I recall, deflection is
inversely proportional to the cube of the thickness of the beam, so
thickness is an important variable. A 1.5 inch thick oak board would
have 1/8 the deflection (7/8 less) than a 3/4 inch thick board.
But to make the design the right size (about 3/4 inch thick) I'd
presumably have to use 1/8" skins and the back piece would be 1/2 inch
thick. How is this functionally any different than routing a 1/2 inch
groove in the back of a solid piece of wood and using a cleat on the
wall? How is the torsion box aspect of the shelf actually related to
the hanging of it? It would seem to me that you can use this hanging
scheme with or without a torsion box.
| >| > I'm not sure I understand the torsion box concept as it applies here.
| >| > If I do understand it then the equivalent hanging scheme can be
| >| > performed without actually making a torsion box. Just make a groove
| >| > the length of the shelf and make a mating piece that mounts to the
| >| > wall. The shelf slides onto the mating piece and is secured by
| >| > screws. So it looks like this:
| >| >
| >| >|
| >| >|----x-------------------
| >| >| x
| >| >|----x----
| >| >| x |
| >| >| x |
| >| >|----x----
| >| >| v
| >| >|-----------------------
| >| >
| >| >
| >| > where I show the side view with the wall on the left and the screw
| >| > shown as x's. This seems like the most secure after the metal bars
| >| > scheme, and possibly easier to implement (?).
| >| >
| >| > Any more thoughts on this?
| >| >
| >| >
| >| I think the shelf with groove would be more prone to sag than the torsion
| >| box. Choice depends on how thin you want the shelf. A few years ago I saw
| >| a photo in one of the magazines of Ian Kirby sitting on a wall hung
| >| torsion box. I don't think that would be doable with any of the other
| >| schemes.
| >As NO-SAG spans are concerned, the following is true for a book shelf:
| >3/4" plywood -- 36"
| >3/4" particleboard -- 28"
| >3/4" Oak board -- 48"
| >1/2" acrylic -- 22"
| >3/8" glass -- 18"
| >These are the maximum spans for a load of 25 lbs. and no additional support.
| Sag shouldn't be a significant issue with the shelf in question. It's
| going to be supported presumably at each stud, so the span is at
| worst 24".
You got that right. The lengths cited are maximum spans for the given material. The comparison following is for a 3/4" X 12" X 48" Oak board. Your recolection may be right for solid material; but, remember, the torsion box is not solid - it is like a corrogated box. As well, the box has a definite weight advantage due to all the air spaces.
| >A torsion-box of 1 1/2" X 12" X 48" will have 2/3 less deflection
| >under load than a similar length Oak board at about 1/3 the cost.
| Are you saying that a 1.5" thick torsion box would have 2/3 less
| deflection than a similar length and THICKNESS oak board? (If so, why
| is this true? I would expect it to be somewhat weaker than a solid
| piece of the same dimensions.) An inch and a half is too thick for
| this shelf. It would look ungainly. As I recall, deflection is
| inversely proportional to the cube of the thickness of the beam, so
| thickness is an important variable. A 1.5 inch thick oak board would
| have 1/8 the deflection (7/8 less) than a 3/4 inch thick board.
| >The torsion box can be constructed from:
| >1/8" or 1/4" skins top and bottom
| >1/8" or 1/4" thick logitudinal core strips spaced 3" apart
| >1/8" or 1/4" thick spacers set every 6" apart.
| >Given 1/4" skins, the front skin would be 1 1/2" wide and the back
| >"skin" would be 1" wide and 1" thick and 47 1/2 " long. This would
| >allow the back "skin" to be screwed to the wall and the torsion box
| >to be screwed/glued to the cleat.
| But to make the design the right size (about 3/4 inch thick) I'd
| presumably have to use 1/8" skins and the back piece would be 1/2 inch
| thick. How is this functionally any different than routing a 1/2 inch
| groove in the back of a solid piece of wood and using a cleat on the
| wall? How is the torsion box aspect of the shelf actually related to
| the hanging of it? It would seem to me that you can use this hanging
| scheme with or without a torsion box.
The torsion box would really be no thicker than any average shelf would appear if there were a 3/4" X 1 1/2" support rabbeted to the front and/or back of a board. Not only does this approach increase the load-bearing capability of the wood, it also adds a look of finish to the shelf and would be a fine way to conceal plywood.
As long as the load to be carried is light, a 1/2" dadoe would work quite nicely. It would still need to be about 1" deep to afford space to hang a few screws.
The torsion box might even be easier to construct than effecting a 1/2" dadoe 1" into the edge of a board - especially if it were a stopped dadoe.
) shows a shelf
that is clearly more than 3/4" thick. I dug out my Instamatic camera
from the basement and measured it at 2.5" high. Scaling from that to
the pictured camera on the shelf, I'd say that the shelf is about 1.5"
If your application really requires a shelf 3/4" thin, I think you
will need to scale back the depth to 3 or 4 inches. Even the crossed
grain construction of a 1/8" plywood skin on a half inch cleat will
not hold much. Making the shelf out of solid wood will be worse - the
"flanges" will split along the grain.
Based on your camera dimension I reached a similar conclusion, though
I think the steep bevel on the edge may throw off this estimate some.
I thought at first that there were CDs at the bottom right, which lead
me to an estimate of 1" thick, but I'm not sure those are CDs. I'm
thinking maybe the shelf is thicker than I thought. It looks like
solid wood, though. If plywood was used they did a darn good job
I don't have a specific application in mind, so I'm flexible. I do
have a space in mind. Is there any difference in the strength of this
mounting scheme done with a groove routed out of solid wood versus an
actual torsion box with the same sized groove?
Idea number 5.
I found these wire supports on WW hardware (actually from catalog, then
found them online).
So here is the idea.
For each U shaped shelf unit:
1. Create a long mortise in both the top and bottom shelf along most of
the edge that faces the wall. Lets say 5/8 wide and 1" deep.
2. Run a 1/8" kerf in the bottom of the mortise, the entire length,
deep enough for the wire
3. Create two wall cleats 5/8" wide by 1" by the lenght of the mortise
- Create countersinked holes at 16" centers for screwing it to the
- Create two sets of holes for two wire supports
All you need to do is screw two of these cleats to the wall, level with
the same center to cenetr as the centerlines of the shelves. Which you
could layout by holding the shelf up to the wall and scribing
One of the nice aspects of this design is the wires fit into a long
kerf so exact vertical alignment is not that critical.
You could put some set screws up into the cleats if you were worried
It's plenty solid without glue. I think some folks have got the wrong
idea about the cleat I was describing- It's not a matter of having
several small cleats to hold up the shelf, but a single long cleat
that runs the entire length of the shelf. Friction and gravity will
hold that thing as solid as a rock- it's basically a torsion box
Aut inveniam viam aut faciam
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If it's threaded rod then what would you do? Mount threaded sockets
in the wall, screw in the threaded rod and then...hammer the shelf
onto the rods that stick out of the wall? I suppose if the rods are
long then falling off shouldn't be a big issue unless someone grabs
OK, a bed hanger just came to mind and I whipped up this as an
illustration. It would use toggle bolts and the holes would be from the
underside and filled once hanged.
Adrian Mariano wrote:
On Tue, 04 Jan 2005 03:53:04 GMT, email@example.com (Adrian
That, and metal bars are not as strong as you may think when they're
sticking straight out of something. The entire shelf becomes a lever
that puts a load on that rod where it's sticking out of the wall.
FWIW, I can bend a 16" x .5" dia. rod of 1018 (weldable) steel over my
knee without much trouble. I'd worry a bit about using it as a shelf
hanger, unless you're taking about some really tough alloy.
If they're into studs, or have drywall anchors, it'd probably be fine.
1/4" sections? The cleat should be strong enough for the setup the OP
proposed, since it distributes the weight along the entire back side
of the shelf. For extra strength, you could make two cleats, and
mount them on top and bottom. It shouldn't come out without a good
amount of upward pressure.
I'd go for the cleat or torsion box. I think you're asking for
trouble with either the bars or the pocket screws. Use the cleat if
you want to avoid having screw heads visible, or use the torsion box
if you don't mind that. Either one should work like a champ.
How big do you think these cleats need to be? I have more confidence
in the cleat for a 1.5" thick shelf than a 3/4" thick shelf.
When you say two cleats are you thinking that it would slide on from
the side, kind of like a sliding dovetail?
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