Counterbores must be done on the mill (Marlin Steel has a four axis CNC Mill - USA Made). There is no limit to the depth of a counterbore in the mill. Our tolerance on the mill is +/-0.005" and we’ll cut it as deep as the client specifies.
Countersinks can be made on the punch (CNC Punch USA Made) with a tolerance of +/-0.030" for shape and +/-0.015" for location. We can not do counterbores on the punch. Check out the attached picture doing a sheet of material (four feet by eight feet) with some counterbores.