I want to start an l girder bench for a layout, I have been reading the second edition basic model benchwork by jeff Wilson. I get the lengths or the girders but is there any rule of thumb aout the WIDTH of the benchwork?
I (eye) girder? Methinks you mean L girder, no?
Benchwork width should be determined by the distance you can reach conveniently, and that dimension can only be determined by the layout owner-operator. If you can only get at one side, it may have to be held to 24-30 inches. Two-side access will allow double that.
Part of my layout, along two structural walls and a garage door, ranges in width from 14 to 32 inches. The two peninsulas are a little over five feet wide, but have viewblocks down their centers. Framing is classic L girder design, but done with steel studs.
A single wide table with a hole in the middle, accessible all around the outside, could be sixteen feet or more across, It would need two L girders on each side of the operating pit, and actual table width on each side of the pit should max out at approximately five feet. It would NOT be the best use of the available floor space.