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- Jun 12, 2014
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There are various iterations on how to use a VFD depending on the system and how it is installed. Most smaller factory installed VFD mills and lathes have 2 mechanical speeds and the motor is used over a 10 fold speed range, usually something like 20-200Hz. The motors are usually oversized, so that the Hp which decreases in a linear fashion below the base speed is sufficient at the lower speeds. They also have an electric blower or are TENV. When you over speed a motor beyond its base speed, the Hp stays flat (up to a point) and you are delivering more Hp to the spindle (when factoring in the mechanical ratio change) then with a fixed frequency motor with a mechanical speed adjustment.
In your situation with a varispeed type of head, your are probably better off using the mechanical adjustment for most of the speed range, also using a fixed mechanical speed would cause uneven wear in one point. What is often done in a mill VFD conversion would be to use a larger (2 or 3Hp) inverter motor and do some form of direct belt drive. With the stock 1 Hp motor you would loose too much Hp using the VFD as your primary adjustment. I also had seen some postings that the Bridgeport pancake motors were a bit more difficult to drive from a VFD stand point, so you may want to go with a 1.5 or 2 Hp VFD, and dial it down to the settings on your motor. The VFD can also provide something on the order of 120-150% overload capacity for up to 1 minute, but this can be a problem for non-inverter motors. There have also been some posting on this site of people using the Lenze or Leeson SMV VFD with good results on this machine. I would set the maximum frequency to something like 75Hz, and use a VFD range of something like 45-75Hz, or use it in a fixed 60 Hz frequency and just use the start/stop and reverse controls.
http://www.globalindustrial.com/p/m...or-series-drive-vfd-nema-1-3ph-1-5hp-200-240v
https://www.wolfautomation.com/esv112n02yxb-ac-drive-1-5hp-208-240vac
In your situation with a varispeed type of head, your are probably better off using the mechanical adjustment for most of the speed range, also using a fixed mechanical speed would cause uneven wear in one point. What is often done in a mill VFD conversion would be to use a larger (2 or 3Hp) inverter motor and do some form of direct belt drive. With the stock 1 Hp motor you would loose too much Hp using the VFD as your primary adjustment. I also had seen some postings that the Bridgeport pancake motors were a bit more difficult to drive from a VFD stand point, so you may want to go with a 1.5 or 2 Hp VFD, and dial it down to the settings on your motor. The VFD can also provide something on the order of 120-150% overload capacity for up to 1 minute, but this can be a problem for non-inverter motors. There have also been some posting on this site of people using the Lenze or Leeson SMV VFD with good results on this machine. I would set the maximum frequency to something like 75Hz, and use a VFD range of something like 45-75Hz, or use it in a fixed 60 Hz frequency and just use the start/stop and reverse controls.
http://www.globalindustrial.com/p/m...or-series-drive-vfd-nema-1-3ph-1-5hp-200-240v
https://www.wolfautomation.com/esv112n02yxb-ac-drive-1-5hp-208-240vac