Large Diam. A= 6 1/2
Small Diam. F= 3
The standard duty bull nose live center is unique in that it utilizes a combination of heavy duty tapered roller bearings in the back of the tool in conjunction with a double row angular contact bearing in the front of the tool to withstand maximum radial and axial loading conditions. Most brands available on the market today simply press a bull nose head on a standard live center bearing set. The result is a tool that is woefully inadequate in comparison.
The taper shank and bull nose head are manufactured from 52100 ball bearing steel and heat treated for maximum strength and durability. The larger heads (nine inch and larger) are manufactured from low carbon steel and heat treated to a deep case depth. The depth case provides longer tool life because it allows the head to be reground multiple times, while the softer core provides the ductility needed when supporting very heavy work pieces.
For best results, choose a bull nose live center that will support the work piece in the middle or upper third of the large end of the nose. This will help balance the weight of the part and carry the load over the bearing assembly.