Originally Posted by
PixMan
This is good theory, but you don't have to switch your toolholder. I suggest you try a Valenite CNGP43.007 SR grade VP9605. The shape of the insert behind where the cutting happens is of no consequence. This insert is a very upsharp edge with ground periphery, and that's what reduces cutting pressure.
BTW g-codeguy...a VNGP and a VNGG are the same. One (VNGP) is the ANSI designation, the VNGG is the ISO designation for the same insert. I think you meant a VNGP will have less cutting pressure than a VNMG. This is true.
Lastly, when the OP says the "machine is locked at 3000rpm", that usually means there's an active G50 limit. Execute a command such as "G50 S4000" to increase it. If it doesn't go higher, then the machine is maxed out at something less than 4000.