Joe in a Cleveland suburb
I am making a step stool. 2 steps. Kinda Shaker looking.
I am making this similar to Christian Becksvoort's stool in #231–Jan/Feb 2013 FWW.

Each step has two mortises and the legs have matching tenons. I want to put a wedge in each tenon. Should the mortise have slight angles to accommodate the wedge? Any suggestions/tips for doing this?

Another question... why, when I chop a mortise by hand, do the walls seem to crumble and chunk out. Shown in the attached picture which is the bottom of one of the steps. They don't have smooth walls. It doesn't surprise me when using big box pine, but this is 3/4 Cherry. In this case I am using a 3/4" bench chisel, not a mortising chisel - don't have one that big. The chisel is, to me anyway, very sharp.

It's probably due to chopping across the grain I suppose. Just currious as to what you guys say.

Thanks for any suggestions.