Replies

1. 
   RANGERP75R | Feb 16, 2003 09:11pm | #1

   Scott

      IMO, yes..... Sit something of equal weight on a sacrifical shelf of same width and material. See if you get sag within a couple of days. Or, just do it. Better safe than sorry. Easy to install at this point. Pain to go back and modify.

   Good Luck....

   sarge..jt

2. 
   camel | Feb 16, 2003 09:17pm | #2

   Scott- You definitely need support in a span that wide. There's different ways. But what you could do is run a 3/8" dado (assuming you're using 3/4" plywood) from front to back, in the middle of your bottom, and glue in a verticle support. You wouldn't see this if your design has an enclosed base. On the other hand an open base, such as bracket feet or similar. You would only want to run your support half way maybe from back to front. You'd see it lying on the floor, but never at standing eye level. Good Luck.

   John E. Nanasy

1. 
   scott57 | Feb 16, 2003 09:36pm | #3

   Thanks for the help.  

   Scott

1. 
   BG | Feb 17, 2003 12:08am | #4

   Scott,

   Just to float another idea...build a torsion box and dado into the side walls...very strong!

3. 
   Lilshaver | Feb 17, 2003 05:17am | #5

   The easy and safe answer is for you to reinforce the dadoed shelf. But, of course, this may compromise, and will surely change, your visual design. So, not being one to always play it safe, I might go ahead and trust the dados. Remember, tv has little "feet" that are near the sides of its case. That's where the load occurs. There is probably little or no load in the center of the shelf span, so deflection really isn't an issue. Only shear forces are present at the shelf ends where they enter the sides. (OK, for the picky ones, some moment forces also are present, but they are small(ish).)

   Make your dados well and leave the design alone. Or, reinforce in any number of ways and don't worry about dropping the television.

   Then again, you could follow other sage advice and shoot the tv. Then you could use the shelf for books. But......they'd probably be heavier than the television, so your question is still valid.

1. 
   scott57 | Feb 17, 2003 05:04pm | #6

   What is a torsion box?

1. 
   BG | Feb 17, 2003 09:49pm | #11

   Sphillips,

   Perhaps the simplist description of a torsion box is a sandwich of two sheets of ply with perpendicular pieces of ply between the top and bottom pieces.  Many of the solutions offered in this thread are close to being a torsion box...

4. 
   JamieFichter | Feb 17, 2003 05:25pm | #7

   Scott:

   Another thing that I have done before is to put a "backbone" of plywood under the shelf.  It is just a scrap piece of plywood the same length as the shelf, and about 1.5 - 2 inches wide (the wider the better).

   Dado the ends of the plywood backbone into the sides of the box so that the piece of plywood is on edge and supports the shelf.  The ends of the piece are supported by the dadoes at the ends.  An alternative is to screw the ends to the box. 

   If you glue the plywood backbone to the shelf bottom, it acts like the web in an engineered wood I-joist.  Very strong if done correctly, and it can be set back from the front of the shelf so that is is not seen very much.  If it is from the same plywood as the rest of the box, it usually doesn't look out of place, but that is obviously a personal opinion, and may not be satisfactory for you...

   Take care,

   Jamie

5. 
   alank11 | Feb 17, 2003 06:25pm | #8

   To know if and how much of a problem i.e. sag you will have with the TV shelf, you can punch in the numbers with the handy sagulator at http://www.woodbin.com/calcs/sagulator.htm

   Alan

6. 
   noone51 | Feb 17, 2003 06:51pm | #9

   Scott, I usually place a strongback at the back of the shelve. I make them 3" wide with a dado running the length which the shelve fits in. You can adjust the position of the dado to provide a lip that keeps things from falling off the back of the shelve, (assuming you're providing airspace behind the TV for venting).

   Your shelve face should be 3/4 x 3/4 with the edge grain up as opposed to facing out. This will give you enough support for the large TV. The new sets are no where near as heavy as the old ones but they still require stongbacks.

1. 
   scott57 | Feb 17, 2003 09:08pm | #10

   Thanks for all of the help,

   Scott