Tim – That is just what I'm speaking of. I too experimented with using an ax to remove the waste after roughing out mortises, mortising axes included. And came to the same conclusion, there is no efficiency there. It is chisel work.

Interestingly, though I didn't mention it above, a number of the descriptions I found refer to removing this triangular waste with a mortising ax. Which is a large part of how I came to the conclusion that these are mostly the musings and suppositions of folks who have not cleaned out many mortises, or taken an ax to many timber frame joints at all for that matter.

Jim – I just rolled back up to the part of the thread where you introduce the mortising ax question, and see that you were wondering out loud if this was a fence post mortising tool. What led you to to wonder if that was a probability?