Replies

1. 
   Frozen | Jun 25, 2010 11:14am | #1

   Possibly.

   In a fully loaded case, lateral pressure on the bookcase sides (caused by stuffing too many books into the available space) could cause the sliding dovetail to shear at the corner. This happened on a bookcase I made with a low-strength wood (Spanish cedar). It may not be an issue with a stronger wood or a wider overhang on the top.

2. 
   RalphBarker | Jun 26, 2010 09:06am | #2

   design factors

   I think there are several factors to consider, including:

   1. what you want the unit to look like - the visual part of the design,

   2. strength and dimensions of the materials - the physical/engineering aspect of the design, compared to expected loads and stresses, and

   3. what the load and stresses are likely to be, both static and environmental. That includes what will be put into the case, whether is is likely to be pushed/pulled across the floor, and whether it might be leaned against by people, adding to lateral stress. The back panel design also plays a role in dealing with lateral stress.

   On a tall case, there are often three fixed "shelves" - the top, the bottom, and one fixed shelf somewhere in the middle, which serves to keep the sides together.  A five foot span is fairly large, so potential sag on the shelves is also a consideration, unless there are vertical members to transfer weight to the frame.

   In general, however, I'd see the sliding dovetails as adding to the strength of the case, particularly if they are glued (although glue can be tricky, depending on the fit).