Hi,
My Z-axis Step/unit= 15000 mm/minutes , and the Mach3 run on Kernel speed=25000Hz .. I can't go above 16IPM rapid... Is that the Kernel speed that can't generate the pulses?

Not sure what you are meaning by "My Z-axis Step/unit= 15000 mm/minutes" I am thinking you may mean 15,000 steps per unit and also you then mention IPM so are your native units Imperial or metric?
If 15000 steps per mm then @25KHz kernel will give you a max of 25000/15000 x 60 = 100mm per min
If the 15000 are steps per inch then it would be 100 inch per min, so not sure where you get the 16IPM frrom as it doesnt work out.
Hood

Thanks Hood,
Actually you answered me as you always do... My mistakes i have set the z-axis 15000 steps/unit (inch) and now i am clear that i can get 100 inch per minute....

ANOTHER QUESTION:
Currently I am driving the Stepper (4.2Amp/phase 1200 oz-in) with 36 volts... Now can you tell me if i increase the voltages ( My controller can support upto 80Volts)  then can i increase my IPM?

I am not the best to ask regards steppers but normally the more voltage you have the  more speed you should get.
Hood