March 2011 - Cutting Tools Overview #2 - Turning
Pro Tips - March 2011
Cutting Tools Overview #2 - Turning
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Figure A: Different Types of Indexable Turning Tools.
Because in turning, the workpiece spins and the tool is stationary, there is only one cutting edge and therefore the concept of flutes doesn't apply as it does with milling tools. That said, the way the cutting edge is presented to the workpiece is vitally important and will vary depending on the type of tool and what material or type of machining operation it is designed for. Figure B shows the different terminology used to describe how a turning tool is presented to the workpieces.
Figure B: Terminology of a Turning Tool.
Tools designed for roughing or working with harder materials may have negative back or face rake angles (see lower image in Figure C) while finishing tools or tools designed for softer materials might have a positive rake angle to better shear the material off as shown in the upper image of Figure C.
Figure C: Negative vs. Positive Rake Angles.
Nearly all cutting tips have some sort of nose radius. The smaller this radius is, the more fragile the tool will be which will make it more likely to break down and need replacing frequently. Also, the slower the tool will need to be fed across the material in order to achieve a given surface finish roughness. Because as the tool feeds across the material, it leaves a spiral pattern of ridges which are larger with a faster feedrate or a smaller nose radius. Please consider the size of radius that you design into the corners of your part, and in general allow a larger radius or give a range which will allow the shop to decide the best tool to use which can lower your costs. Also do not specify a surface roughness value that is finer than you need, as that too will drive up costs. Some types of tools have what is called a wiper insert which looks like this.
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Part of the Month:
Every month we feature a really cool part that we have made. March's Part of the Month is a stainless steel manifold. With multiple ports, o-ring grooves and threaded holes this part has requirements for high tolerances, fine finishes and excellent deburring. This is a good example of a part that can be made complete on one of our mill/turn lathes.
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