Long-Span Shelves
Ideas and resources for dealing with long shelf spans. December 30, 2005
Question
My client is looking for free-span paint grade library shelves greater than 40" wide x 11" deep. My options are wide open for material choice, but a center stile and/or partition are out. I can't tolerate any sagging, so I'd love to tap into your experience on how to make long spans that are sag resistant.
Forum Responses
(Cabinetmaking Forum)
From contributor A:
I'd do 6/4 soft maple, planed down to 1-1/4" final thickness. You could store your encyclopedia collection on a shelf
like this with no discernable deflection. Make sure you price accordingly. Spans over about 44" should be a torsion box construction.
From contributor B:
I've used white oak with a 5' span, 1" thick with no sag.
From contributor C:
If you are going paint grade, look at 5/4 Soft Maple for solid wood shelves.
From contributor D:
Hickory is the strongest wood I've run across. Use grain filler and you’re ready to paint.
From contributor E:
Try this link:
Sagulator
From Gene Wengert, technical advisor Sawing and Drying Forum:
Check CABINET MAKER magazine, August 2005, for a good bit of information about shelf design, including effect of species (denser is better), thickness and so on. Solid wood is much better than composites.
From contributor F:
For that span I have used 1-3/8" solid core birch doors - rip and edge – it’s quick and easy. I just finished a shelf unit with 12" x 60" fixed shelves. I used two 3/4" plywood rips, let in 1" steel c channel between layers at front edge. There was no sag and no problem. I have had problems with solid wood shelving cupping and or twisting over time. Laminating two pieces helps with this problem.
From contributor G:
To contributor A: What is torsion box construction??
From contributor H:
Try to get past issue of Better Homes and Gardens, WOOD, March 2004 issue 154. This is the best information I have seen regarding this question.
From the original questioner:
These are all great ideas, and the online resources are all good. I especially liked the Sagulator- even if the specific material you're looking at isn't listed, you can get a good sense for the relative impact on shelf sag by changing one parameter at a time (width, depth, etc.) and seeing the effect it has on sag.
