We at Cutting Tools Chicago aka General Cutting Tools along with Ingersoll Cutting Tools are going back to the basics of face mill design to select a tool to match your application.
When milling with an indexable face mill, the work piece, machine, and fixturing must all be as rigid as possible. This will help ensure efficient use of this type of tool and produce the results required. Only cutters using indexable carbide inserts will be discussed here.
Applying Cutter Geometry
Insert cutting edges may be positioned relative to both radial and axial planes in positive, neutral, or negative rakes. Neutral rake is generally not used due to the shock of the entire cutting edge impacting the work piece simultaneously.
The combination of radial and axial rakes determines the shear angle. Three basic combinations are available: negative radial and axial, positive radial and axial, negative radial/positive axial, and positive radial/negative axial.
Double negative geometry is the traditional starting point for rough milling cast iron and steels when horsepower and rigidity are adequate. The double negative insert design provides the strongest possible cutting edge and can withstand heavier chip loads and considerable cutting forces.
The increased cutting forces generated by this geometry will consume more horsepower. Double negative cutters also require greater machine, work piece, and fixture rigidity.
Double positive geometry provides the most efficient cutting action due to its increased shearing angle. Although not as strong as double negative, entry impact and cutting forces are greatly reduced, making it a good choice for older, less rigid machines or where horsepower is limited.
With double positive geometry, the peripheral edge, in both the radial and axial planes, leads the insert through the work piece creating a true shearing action. This makes it the best choice for non-ferrous materials and many soft, gummy stainless steels.
Negative radial/positive axial geometry combines some of the advantages of both double negative and double positive. Negative radial rake provides strong cutting edges, while positive axial rake creates a shearing action. A positive axial rake directs chips up and away from the work piece. This prevents chip recutting and takes heat away from the work surface and the cutting edge.
Positive radial/negative axial geometry reduces power consumption while still providing a strong corner cross-section.