Pardon the Interruption

Selecting the proper tool for your interrupted-turning application requires an examination of the part and the process

September 1, 2009

Part design, raw material, and the machine tool being used are all variables in the tooling selection process. And, as the machining process becomes more difficult because of the part features or the material being cut, novel tooling may mean a reduction in costs and in headaches.

“Before any chips are produced, we need to have an intimate understanding of the part that is being created,” explained Steve Geisel, turning product manager for tooling supplier Iscar. “There are many variables that affect the machining process, and we need to be able to not only recommend a tool, but in many cases, recommend a way of producing parts that may be new to the customer.”

The material being cut, machine tool horsepower, and coolant are just a few of the variables that need to be understood before moving on to tool selection.

In the beginning, however, it is the features of the part, such as shoulders and holes, that need to be examined.

“As the envelope gets pushed in tooling, machine tools, software, and controls, parts can now be created in ways that weren’t previously possible, and it is often up to us to be able to convey this to the customer,” said Geisel. “Our job is to know how to take the part design and make the part in a way that is both feasible and economical.”

Cutting Load

In interrupted turning, whether it’s a light or heavy interruption, the tool plays a very important role. In this type of operation, stress is put on the nose radius, which is the weakest part of the tool.

“There is a definite need for tool strength in this type of cutting,” said Geisel, “and the bigger the radius, the stronger the tool.”

There is more than one way to create strength, however.

“What we like to do, provided we don’t have to create a 90-degree corner, is spread the load over a greater area of the insert by using a 45-degree approach angle or even as much as 75 degrees,” he explained.

When the insert is tilted in this manner, the load is transferred to a longer area of the insert. This will also allow more aggressive feed rates to be used, which means more material will be removed.

Cutting in this manner, as well as new designs in insert technology, keeps the strength of the insert where it needs to be.

“It really is about creating a balancing act between tool stability and insert strength without putting pressure on the part or putting heat into the material,” said Geisel.

His advice? Be realistic in your approach. If your application warrants it, use a heavy insert, but this is not necessarily needed all the time. In fact, it is the edge preparation and chip former that are generally the keys to successful interrupted turning.

“People sometimes think only about strength when the chip former, edge prep, and coating are just as important,” he said.

These are areas that are constantly changing as the tooling suppliers’ R&D bears fruit.

“In some applications if you are still using the same tool that you were a few years ago, then you are behind the times,” said Geisel.

For more information, visit www.iscar.ca.