SHERLINE 35° Inserted Tip Carbide Tool Holders

Design of the Sherline carbide toolholders

Recent increases in cost for commercial tool holders have made them very expensive for the hobbyist. We decided to make our own holders to help keep costs down. To further reduce costs and to increase the value, we designed them to be made in pairs with a "left" and a "right". The holders are case hardened and then given a black oxide finish.

The offset angle of the tip makes it easier to accomplish certain cuts. For example, by using the toolholder square with the crosslide, you can turn an O.D. up to a shoulder and then finish by backing the tool out while still maintaining the proper tool clearance. The tip of the cutting tool is .375" from the bottom of the holder, which is the industry standard.

Carbide tools vs. high speed steel

I would like to emphasize that I believe the prime method of cutting metals on a miniature metal cutting lathe should be high speed steel. It’s inexpensive, easy to sharpen, and can be shaped to make "form" tools. Insert tooling is expensive and can’t be resharpened or shaped, but it can be a lifesaver.

The obvious difference between carbide tools and inserted carbide tools is the tip is held on with a screw rather than brazed on to a piece of steel. This fact has a lot to do with the success of insert tools in recent years. Steel and carbide have slightly different expansion rates which can cause premature failure of the carbide tip on brazed tools. It is surprising that a small screw will hold these inserts tight enough to accurately cut metal, but they do. We run 20-horsepower computer-controlled lathes at Sherline that can remove metal at a rate of 2 pounds (1 kilogram) a minute with these tools and have few failures.

The reasons I believe insert tools should have a place in your shop is that they are ready to use, they hold their cutting edge when cutting exotic metals or abrasive materials, and they can speed up the cutting process.

Cutting speeds with carbide tools

Normal cutting speed rules don’t have to be considered to the same extent as when using high speed steel. Stainless steel can be cut at triple the rate over high speed steel with these tools. This puts you in a better horsepower range on the Sherline motor. Another interesting fact is that you can get a better finish on some steels, such as cold rolled, by turning up the RPM. Insert tools don’t need cutting oils to work well, but I still use a few drops now and then. This can be an important fact when working on your kitchen table.

Positive rake tools were chosen because they provide a better finish with lower cutting loads. Only tips with a positive cutting edge can be used in these holders. To get maximum life out of these tools, be sure to increase the "feed" as you increase the RPM. The chip should have a tight curl to it and break off into short lengths.

Another plus for insert tools is their ability to cut hard or abrasive materials. Don’t plan on machining down the shanks on end mills with them, but you can cut through a work-hardened surface on stainless steel with ease. Carbide tools can simplify many machining operations, but will never solve problems caused by poor machining practices. As with all machining operations, ALWAYS WEAR EYE PROTECTION.

Choosing a cutting tip radius

Another choice I made was the .015" (.4 mm) radius on the tip. A large tool radius can give good finishes on a full-size machine, but it can cause havoc on small diameter parts or miniature machines. Large-radius tools create high tool loads because of their large cutting surface. On the other hand, a radius smaller than .015" will chip too easily.

Toolposts to hold these tools

Sherline offers two toolposts that will hold these 3/8" shank tools. The P/N 7600 toolpost holds both a 3/8" square and a 3/8" round tool holder. The P/N 3008 two-positon toolpost holds a 3/8" tool shank on one side and a 5/16" tool on the other side.

Joe Martin, President and Owner
Sherline Products Inc.