You have no factual basis for making that statement, and I'm quite certain Tormach, being a company that does very thorough engineering on their products, would NEVER operate the motor outside its manufacturers maximum ratings. To do otherwise would expose them to a HUGE potential liability were one to fail at high speed. 1750 RPM is undoubtedly the *base* motor RPM, measured at a 60Hz frequency, which tells you absolutely NOTHING about its safe maximum RPM capability at higher frequencies. Inverter-rated motors are *designed* to be operated well above their base RPM, typically by 2-3X or even more. Were this not the case, there would be no reason for every inverter sold to be capable of running at least 120-200Hz or more.
Regards,
Ray L.