Interesting I've always looked at them with blacksmith's eyes, the long handle to get away from the heat of a large rectangular bar. Did the wheelwright use them in making the hubs (turning) or in shaping other wheel parts (spokes and felloes) with draw knives and spoke shaves? My thought is that the handle seems too long to be used effectively on a lathe, especially a treadle lathe. I'll have to go back to books a bit more I think!
Graeme