Machinist

[Lawrence London <lfljvenaura@gmail.com>]

http://conradhoffman.com/stellite.htm

Cast Alloy Lathe Tools

Stellite J - Tantung G - Blackalloy 525 - Crobalt

With the refinement of carbide insert cutting tools, many believe cast alloy tools have been rendered obsolete in commercial machining. That's certainly true for run-of-the-mill CNC work in aluminum and free machining steels, however some applications remain where cast alloy tools should be considered.

These alloys possess properties somewhere between high speed steel (HSS) and carbide. They can be ground with a standard grinding wheel, though the process can be a bit slow going. They're tough and work well on interrupted cuts and on castings that would tend to chip carbide, though they're more prone to chipping than HSS. High lubricity is another feature and that prevents welding of material on the tool tip. They cannot be annealed and thus retain their hardness and cutting ability to red heat. In general, they will operate at 2X or more the speed of HSS, but not that of carbide.

For home machinists cast alloys are an excellent choice for less rigid and lower speed/power machines that can't take maximum advantage of carbide. They lend themselves to off hand grinding better than carbide. The biggest obstacle for the home machinist is getting tool blanks at a reasonable cost.

You may find the occasional cast alloy tool in used and surplus tooling. The alloys are completely non-magnetic so you should always carry a magnet when inspecting odd lots of tooling. The etched names will often be ground away and the magnet will quickly separate HSS from cast alloy tooling. In general you are looking for the following:

1. Stellite Star J (and possibly other Stellite types)
2. Blackalloy 525
3. Tantung G
4. Crobalt

Modern cast alloy tools will be ground on all sides and look similar to HSS tooling. They resist corrosion extremely well and may stand out in used tooling for that reason. On the other hand, don't be put off by the appearance of older cast alloy tooling. Some of it may look like it was cast in a backyard barbecue grill. It will be dark in color and have significant imperfections and poor grinding. Others will have passed it by, but their loss is your gain. New cast alloy blanks are still available from at least three manufacturers but don't expect to get them for import or flea market HSS prices!