Shop Doc – Tool Holder

Todays Machining World Archives June 2007 Volume 03 Issue 06

Dear Shop Doc,

There is this tool holder in our Brown & Sharpe tool crib that is some type of turning tool. No one here has ever used it. It has two blades but no rollers or backrest. One of the more experienced guys here said it’s a rough turning tool but thought they were hard to use. Can you tell me anything about this tool?

Just Curious

Dear Curious,
Your information is partly correct. The correct name for the tool in question is a balanced turning tool, and it isn’t difficult to use. The balanced turning tool is excellent for removing large amounts of stock at maximum rates. There are three primary ways to set the blades, depending on the requirements of the manufacturing process. In all of those cases the blades cut tangentially to the stock. Some shops have gone to carbide blades allowing for increased feeds and speeds.

The first method of setup is a true “balanced turning” application. The blades are each set at the same turning diameter; each blade removes the same amount of material that is determined by the depth of cut and the feed rate. The feed rates can vary from .005” per revolution up to .01” per revolution. However, the depth of cut can range to .250” deep, allowing .500” stock removal for one pass. The full depth of cut for each blade and the feed rate determine the thickness of the chip.

The second method for rough turning is to set each tool to remove one half of the total stock that needs to be removed. One half the full depths of cut and the feed rate will determine the chip thickness in this scenario. I personally have removed up to one inch of stock in one pass with this method, using 5/8″ turning blades.

The last method is to use the two blades as a rougher and a finisher in one pass. In this case, one blade removes 80 percent of the material. The second (finish) blade is set behind the rougher by at least the thickness of the chip (feed rate), and it removes the last 20 percent of the material. Some operators will stone the finish blade to give it some drag on the material. The feed rate will determine the quality of the finish in this case.

In all cases, the tools need to be centered and relieved properly to avoid rubbing. Three to twelve degrees, depending on material type, is a good top rake. The tool holder provides the side clearance when the blades are centered properly.

These tools are not difficult to set and they allow a much greater stock removal per pass than roller box tools. The roller box tool is preferred when a tight tolerance or superior finish is required. Good luck in using your “new” old tool.

George Morris
AMT Machine Systems

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