Jacob":thc8mxv4 said:
I wish someone could explain to me what is wrong with the convex bevel. It obviously worries people but nobody can explain why. There's no logical objection to it, and it works in practice. What is the problem?
Ok, strictly in the interest of peace and goodwill to all readers, let's have a little try at explaining.
I suspect that in some of these discussions, we are not all talking about the same things, so let's try some pictures and work out what Jacob means by a rounded bevel and why some people might think it's a bad thing. When I first read about rounded bevels on here, I think I got the wrong end of the stick, but I now think I might understand what is meant.
Have a look at my first diagram. It's a cross section of a chisel. The black line is the short of sharpening you might get with a jig - it's ground at 25° and then honed at 30°, so you get two angles where flat surfaces intersect, at X and Y.
I've then superimposed an orange line, showing what I think a rounded bevel is. The difference is that the sharp intersections at X and Y have been rubbed away
below the places where they would have been.
Taking away that extra bit of metal - which was never going to cut anything - is the 'rounding'. I really can't see anything wrong with it.
Down at the tip, the cutting edge is much the same, even if we're measuring the angle of a tangent to the curve instead of the angle of a flat surface. It's still sharp.
So why the apparent objections?
My guess is that at first glance, people might be imagining that this is a rounded bevel:
That is a chisel with the flat side rounded where it shouldn't be, and is not going to cut in the way that we need a chisel to cut.
So, Jacob and everyone, are my diagrams helpful?