shavinghorse 

Shavinghorse: A large hand made saw horse, with a built-in saddle, in front of the saddle is a vice which holds a large sharp blade used for shaving the bark from wooden post, such as a fence post.

Shavinghorse's were commonly used during the late eighteenth and early nineteenth centuries. Also the area with the vice/blade attachment was known to be very wide on the shavinghorse.
Many earlier settlers when referring to someone who had a larger than average head would often refer to the person as "having a head like a shavinghorse"

Wow Bob, did you see the size of that dude's head? - he had a head on him like a shavinghorse!

shavinghorse by Ole' Moe March 21, 2017