Replies

1. 
   jarcolio | Jul 21, 2005 03:13pm | #1

   30" max for regular books -- 36" for some boos and knick knacks -- 5' is way too long

2. 
   Tharrett | Jul 21, 2005 03:23pm | #2

   I have made some built in book cases before and utilized mdf for the sides but never for the actual shelving.  A 5' long mdf shelf would certainly sag under it's own weight in little time without significant support.

   Attached is a picture. The actual shelves were 3/4" plywood with a strip of pine glued to the front (of the shelves).  All shelves are adjustable except for the mid height one.  Thinking back, I would have used a larger strip in front to give the appearance of a thicker shelf.

    

   
3. 
   AJinNZ | Jul 21, 2005 04:01pm | #3

   I use MDF for the sides and a thin sheet for the back.

   Pine for the shelves, dadoed into the sides. That way they hold up to weight really well.

    

   As for a 5' wide shelf, ply or pine. Still need that front piece to make it stiffer. However I am thinking a thicker back with glue and some decent nails would likely do it.

   I never had one of mine come back...........

    

   Whatever it was.................I didnt do it.

4. FHB Editor
   JFink | Jul 21, 2005 04:25pm | #4

   MDF, even 3/4" in, will flex over 5' like a wet noodle. If you can't go less than 5', consider making a torsion box construction, or reinforcing the length with hardwood strips under the front of each shelf...either way the shelf will appear to be thicker, which will look better anyhow.

   Hope this helps.

    

   Justin Fink - FHB Editorial

1. 
   basswood | Jul 22, 2005 02:55am | #10

   Here is a photo of what you have described (in a better size):

   
5. 
   DDay | Jul 21, 2005 09:26pm | #5

   This will help.  http://www.woodbin.com/calcs/sagulator.htm

6. 
   CapnMac | Jul 21, 2005 10:06pm | #6

   of glueing a 1 1/2 inch strip to the front and back edges to make them stiff.

   Rabbet that shelf into the strip, and use a very stiff hardwood for the strip, too. 

   I just ran 60' long, 1.5 tall, .75 thick White Oak with 100# through the sagulator and got a deflection of 0.75"--so you might just ignore what I said previosly . . .

   Hmm, fir ply & max stiffness osb at 12x60x.75 both deflect 0.56.

   HD MDF, 12 x 60 x .75 comes back 1.33" sagged--that's not adding much to the oak.

   Sounds like you need some sort of mid-span support.

   Occupational hazard of my occupation not being around (sorry Bubba)
7. 
   mbdyer | Jul 22, 2005 01:19am | #7

   MDF will sag.  No doubt.  Five foot is long for hardwood unless you use framing stock dimensions.   A torsion box is probably best.  1/4 inch for top and bottom sheets, 1x's for the ribbing, 1x2 for the edge and hang rail.

8. 
   basswood | Jul 22, 2005 02:42am | #8

   Here is a set of six foot shelves I made out of MDF...a cherry veneer MDF torsion box faced in 2-1/2" cherry (two layers of veneered 3/4" MDF sandwiched over an frame built of 1" thick poplar. 1" x 1" hidden poplar cleats were screwed to the walls.

   6' span and no sagging even loaded with cookbooks.

1. 
   JayFlannery | Jul 22, 2005 02:54am | #9

   I *think* he said he was putting a front & back strip on...I woudld be interested in what everyone thought of that...strip material taken into consideration, of course.Jay

9. 
   DougU | Jul 22, 2005 02:58am | #11

   Greg

   I think 5' long shelves are to long but when I had to do similar I've glued two pieces of ply together and didnt have any problems with sag.

   1 1/2" of ply is prety damn rigid and doesnt seem to sag.

   Doug

10. 
    SteveInCleveland | Jul 22, 2005 03:19am | #12

    Five feet is pretty long.  Can you divide the length and make two units?  I try not to go over 36” for shelves.  Especially if they’ll be loaded with books, etc. 

     

    I make custom shelving units quite frequently.  For paint grade cabinets, I use ¾’ MDF for the shelf.  I also glue a 1 x 2 piece of poplar along the front edge of the shelf.  When glueing up, I shoot 1-1/2” finish nails into the poplar to hold the piece in place, and then clamp the shelves with my Bessey clamps to make for a tight, strong glue joint. 

     

    I nail the top edge of the poplar about 1/16” above the top of the MDF.  That way, after the glue has set, I can use a flush trimming bit in my router.  After priming and painting, you can’t even see the joint.

     

    I’ve attached before and after photos of one recent project.

     

    Good luck.

     

     

     

    "Preach the Gospel at all times; if necessary, use words."  - St. Francis of Assisi

    
11. 
    maverick | Jul 22, 2005 04:43am | #13

    >>Any thoughts on wheather these will sag over time would be appreciated

    Yeah, over a time span of about 2 minutes.

     I suspect you are gonna paint them since you are considering MDF, so spend a little more and buy CDX plywood, its much stronger. No need to buy AC ply.