On a hunch I searched for armature trimming tools and found something similar in an old booklet "How to True Armatures, Bulletin 2A" by the South Bend Lathe Works . I think parts are missing but it might be for undercutting the mica in armatures. The square block mounts it to a holder and the handle moves the cutting blades.
Thanks for the information I am now the proud owner of an armature trimming tool. It will be displayed in my vintage tool collection, in my vintage machinists chest.armature trimming tools