Double reduction gearing drives a high-speed grinding wheel revolving on an axis 3/64” from the center of the grinding seat
The Hall-Toledo pilot guides the grinder so that it produces a true seat, one which is properly centered on the valve guide. One end of the pilot accurately fits the valve guide while the other end has a close running fit in the central bore of the tool. At this point, a replaceable hardened bushing or “eccentric shaft” takes the wear.
A micrometer feed screw in the top of the grinder controls the grinding speed by adjusting the wheel’s position relative to the seat. A feed rod, which is set for position and then locked in the feed nut, extends downward to rest on top of the pilot and carries the weight of the grinder during operation. The operator has complete control over how much material is removed from the valve seat.
Hall-Toledo “Point-Contact” grinders incorporate two grinding motions: