ThomD
>I don't think the angle on chisels is determined by the requirements of toughness in penetrative cuts. One can certainly make chisels that don't stand up to a hit and vibrate nastily. Those problems tend to have their origin well above the edge. But the edge breaking down, that seems an odd reason for determining chisel angles, just because it gets said over and over, the tools tell a different story.

Many tools whose edges are messed with quite horribly, from axes to plane blades have lower angle edges/bevels. I think the guiding principle is how the bewels set the edge aside when they are hit. A very narrow 3 degree blade can sometimes fully penetrate a joint in softwood in one cut from each side. But barring that you need to guide the chisel and determine the notch dimensions, and one does that with the bevel. It is another reason I generally prefer not to have micro bevels, though if they are present it won't ruin my party.