Collet on commutator welding machine
In commutator hostacking machine, collet is not broken, only shaft holding inner dia is increased.
Before the collet broken, did you check if the V holder was in proper position and wheather the armature and V holder base are working properly?
Please check the V holder and adjust it in proper position, then the collet won't be worn out easily,
Loose size is not so big .Some time Armature not moving along with indexing because of loose grip. May be there are some issues of improper hardening of collate.