motor speed reduction

If you won't use a VFD, what about DC?

below 50% load not working already tried with 40v dc motor about 0.6hp motor

Variable pitch sheave?

Please clarify the statement below?

after 3:1 gear ration i am making operation of (surface grinder machine)travel at very sharp inch about 3 to 5 mm.

What sort of mounting, shaft size?

my motor rpm is 840

two v belt connected between motor pulley and drive shaft.

when motor pulley rotate three turns drive shaft complete one turn.

when drive shaft rotate one turn my mechanism travel 3 mm.

if i apply very short time pulse for motor on ( around 1 sec Approx.) mechanism move up to 5mm.

todays my observation are as follows even if i apply brake for slide still it moves as is.

if motor run at 200 to 300 rpm may problem solved. ( but without loosing torque) else may be required gear box. for reduction.

Drive a ball screw? Use hydraulics? Use a DC motor, or a stepper motor?

rewind the motor to 8 or 12 poles

If you need just a fixed reduction ratio, chain or gear reduction gears provide higher ratios, than belt. Planetary gears can provide up to 100;1 reduction.

But if you want variability:

Three phase motors are designed to run almost synchronously with the 3 phases. Their slip from it generates the current that drives them. So, VFD (variable frequency drive) is the ticket.

But since it is such a low power motor, a brush motor with an electronic feedback driver (sensing speed) would fill the ticket nicely.