I apologize for the English response, but I strongly recommend that anyone who wants safe and effective control of the motor to use a VFD. I have mine set for a 10 second ramp on start, which greatly reduces wear on the entire gear train by eliminating the high starting torque and shocks. This protects all gears and bearings. For stopping, I have my drive set for 2 seconds, which quickly stops the VFD without shocks. The VFD also provides digital inputs which are used for additional functions. I wired the original forward / reverse switch for those same functions and I wired the original brake position to the VFD and programmed that input for an emergency stop. This stops the entire lathe instantly and does work well. Properly adjusted and aligned, the belt should not be coming off of the pulleys. If this is happening. My original joystick control does exactly what it did with the original control circuit but everything operates much more smoothly. I can even switch from full forward speed to full reverse immediately and the VFD will slow the motor to a stop and then ramp it up to full reverse very smoothly and much better than the original control system was able to do.
If you are starting the lathe in cold weather, I would recommend using a longer start and stop ramp if you are worried should damage to the belt. But, you should understand that starting the motor at full speed, without a VFD will put the maximum stress on the belt. The only remedy for cold starting is a VFD because it is the only reasonable way to slowly bring the lathe up to operating speed. Although there are other ways of doing this electronically, none of the other approaches are as cost effective as a VFD.
The manuals that come with VFDs are thick with a lot of reading. But, with patience, you can figure out how to make the correct connections and then make the correct program settings so that the lathe operates exactly the way you want it to. The range of control that a VFD provides goes far beyond what the original control circuitry could provide.