MY63 wrote:I have started making my bench for under the MFT style top and am a little concerned over the size of my rails. My legs may be a little over size at 100mm but I am a little worried my rails may be a little on the small side at 35mm x 75mm is this heavy enough or should I stick two together and have 70mm x 75mm rails.
The other question is how deep should the mortices be.
Rigidity of a beam increases linearly with width and by the cube of the depth. So no great advantage to doubling up the width.
Mortise depth - at least 50% when you can but why not go all the way through and wedge them for this sort of job where strength is more important that looks. Even wedged tenons can look pretty too.
Bob