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Negative Rake Angles versus Cutting Performance

      Since the birth of the indexable insert, all turning tool holders were manufactured with 5 negative rake angles in both directions. Later this became the ANSI and ISO industry standard. It would be interesting to find out what the reasons were and why that was done.

      In the 1980’s several research labs ran tool life tests comparing various degrees of negative rake angles. They all came to a same conclusion that, an increase of the negative rake angles increases tool life.

      As we all know, negative turning inserts have 90 sides. This also means that an increase of the top rake will increase the side clearance angle. An increase of the side clearance will absolutely increase tool life. The following sketch uses a .010” wear land criterion and compares a 5 top rake angle to a 10. The theoretical result is that, the 5 rake has .0009” wear life compared to the 10 rake with .0018”. The 10 rake therefore produces double the tool life. In reality of course it will vary but still in favor of the 10.

      The Streamliner™ negative tool holders have these enhanced top rake angles. They are matched to each insert geometry and lead angle. The steeper negative rake angles produce a slight amount more heat that help crimp the chip faster, producing a tighter chip curl and better chip control. Improved tool life and chip control are common.

Streamliner & Associates, Inc

Copyright 2007
Made in the USA