Ideas for bookcase shelf dado
I've been trying to come up with the best joint detail for dadoing fixed 3/4" plywood shelves into a bookcase on all 3 sides. I need this much support because I'm using the shleves to store heavy reference books and they will be completely loaded down. I will have a 3/4" nosing to add strength and casing trim all around the front face of the bookcases which should hide these dados completely.
I usually try to design my details to allow some tolerance so I don't have to build joints that fit perfectly. I'm using a router and was following an example from a magazine that used zero clearance hardwood templates and the actual plywood shelf as a guide to set the dado template width. This was fine except after cutting I learned a few things.
First thing I learned was not all 3/4" plywood is exactly the same thickness. My first set of shelves were cut from two different pieces of plywood and they vary by as much as 1/64 to 1/32. This didn't seem like much until I installed the shelves. Then a small horizontal gap at the top of the dado shows up like a sore thumb. So I thought I got smarter the second time and cut all the shelves from the same piece of plywood.
However, the second thing I learned was that sanding the shelves prior to assembly will also change their thickness just enough to create more horizontal gaps.
My initial solution was to rabbet the top and bottom of the shelves to create a thinner toungue that would be easily concealed by the thicker shelf. However, since I do not have a router table yet that's alot more setup than I want to do for these. After further thought I came up with the joint on the attached picture. I think by cutting a rabbet just into the top of the plywood shelves I'd create a toungue that would be easily concealed while still allowing tolerance. I'm pretty sure gravity will close up any potential gap at the bottom of the shelves anyway. In order to keep from having to make each shelf exactly the correct width to prevent vertical gaps between the shleves and the sides, I realized I could just make the dado bigger than the shelf toungue in both directions. I think this could solve the problem.
Anyone have any better ideas?
Last edited by Steve M.; 06-25-2013 at 03:29 PM.