09-23-2016, 03:19 PM
Negative rake inserts always seem to prefer a depth of cut equal to or greater than the nose radius, and feed rates that would make a screw-down or top-clamped (positive rake) insert blush.
When finish with a negative rake insert is troublesome, chipbreaker (top form geometry) is often the solution. High positive geometry can help by reducing cutting pressure while doing more shear action than displacing the material. Note that the actual sharpness of the edge can matter as well. Many positive rake inserts have a ground periphery rather than "as sintered" that is found on a CNMG. A sharp, ground edge reduces cutting pressure even more. Lastly...approach angle. The obtuse angle (100º) angle of those CCMT and CNMG inserts, presented to the face of a part is stronger and further reduces cutting pressure by chip thinning action. You both have that type of toolholder, no better way to use up the corners of inserts which you can find in my carbide scrap bin. ;)
Of course with carbide tooling the rigidity of the workpiece and tooling is paramount to good performance. Weakness is flexing and a chatter, both of which can be detrimental to tool life of carbide.
When finish with a negative rake insert is troublesome, chipbreaker (top form geometry) is often the solution. High positive geometry can help by reducing cutting pressure while doing more shear action than displacing the material. Note that the actual sharpness of the edge can matter as well. Many positive rake inserts have a ground periphery rather than "as sintered" that is found on a CNMG. A sharp, ground edge reduces cutting pressure even more. Lastly...approach angle. The obtuse angle (100º) angle of those CCMT and CNMG inserts, presented to the face of a part is stronger and further reduces cutting pressure by chip thinning action. You both have that type of toolholder, no better way to use up the corners of inserts which you can find in my carbide scrap bin. ;)
Of course with carbide tooling the rigidity of the workpiece and tooling is paramount to good performance. Weakness is flexing and a chatter, both of which can be detrimental to tool life of carbide.