Yes, excess weight on a shelf can cause the shelf to slip out of the dadoes on
the sides. One way around this is to screw through the sides into the shelf.
This is screwing into the end grain of the shelf which is not the strongest
grip but still will help a lot. A second way is tobiscuit the shelves into the
sides and not use a dado. A third way is to put a cleat underneath the shelf
and screw the cleat to the side and then screw the shelf to the cleat.
An entirely different way is to strengthen the shelf. If, for instance, you are
using 3/4-inch thick plywood for the shelf, you could add a 2-inch hardwood
facing strip to the plywood edge which would substantially strengthen the
shelf. Since your shelves are only 28 1/2 inches long and are only expected to
support 20 pounds of weight, you should not have much of a problem if you add
the edging strip..
Here are a list of shelf weight limits that should be useful. All numbers are
for a shelf 30-inches in length and 11 inches wide and the weight limits are in
pounds per foot.
A plywood shelf 3/4 inch thick will support 13 pounds per foot and that same
3/4 inch shelf with 2-inch red oak edging will support 39 pounds peer foot. MDF
3/4 inch, on the other hand, will only support 4 pounds per foot but with a
2-inch red oak edging it will support 30 pounds per foot.
Eastern white pine, 3/4 inches thick, will support 13 pounds per foot, 1 inch
thick will support 32 pounds and 3/4 inch with a 2-inch white pine edging also
will support 32 pounds. If you get into poplar, then the 3/4 inch shelf has a
weight limit of 17 pounds per foot, 3/4 inch with 2-inch poplar edging will
support 39 pounds and 1 inch thick poplar will support 41 pounds. For red oak,
the weight limits are 21 pounds for 3/4 inch, and 47 pounds for either 3/4 inch
with 2-inch edging or 1 inch thick red oak.
Hope this helps.
--
Larry Martin
Woodworking for the Blind
--joining the world of blind wood workers
-------------- Original message ----------------------
From: "Max Robinson" <[EMAIL PROTECTED]>
> The weather profits are saying we should have a string of 50 degree days
> starting next week. That means I will be able to get out to my shop and
> work on the radio desk. A friend pointed out a potential problem with my
> design. He says if the shelves sag under the weight of some of the
> equipment the ends of the shelves could pull out of the dados. How can I
> secure the ends to the sides to ensure this won't happen. All shelves have
> an unsupported span of 28 and a half inches. One is nine inches deep and is
> likely to support as much as 20 pounds. It can be supported along its
> length at the back by fastening it to the one quarter inch back panel. The
> other is 16 inches deep and is likely to support about the same weight. The
> back panel will not extend to that shelf to allow for ventilation. It will
> be supported only at the ends by the dados. What are your thoughts on this.
> I built a workbench about 35 years ago and the upper level which was for
> holding test equipment was 6 feet long and one foot wide. It was supported
> on 2 by 4s at the ends and along the back. The front edge began to sag in
> the middle after about 20 years. It supported about 40 pounds of stuff. I
> don't want my radio desk to sag and come apart after a few years.
>
> Regards.
>
> Max. K 4 O D S.
>
> Email: [EMAIL PROTECTED]
>
> Transistor site http://www.funwithtransistors.net
> Vacuum tube site: http://www.funwithtubes.net
> Music site: http://www.maxsmusicplace.com
>
> To subscribe to the fun with tubes group send an email to,
> [EMAIL PROTECTED]
>
[Non-text portions of this message have been removed]
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