April 10, 2010
October 16, 2011
May 30, 2010
Kenny, forget the jackshaft…seriously.
And increase the horsepower by X 2.
The 1800 rpm motor has twice the starting torque of a 3600 rpm. It also has twice the number of poles in the motor which helps this. At reduced cycles you have reduced torque, even with the extra torque boost programmed into the VFD. The only way to keep within the torque requirements of your machine when running low rpms is to increase the motor horsepower.
I have attempted to use a 2 hp 3 phase 3600 rpm motor, in place of a 1.5 hp 1800rpm single phase, to get variable speed on my mill. It would not even start it rotating unless rotated by hand first, in the lowest belt setting. And hopeless for cutting, even at high rpm.
And using a 5 inch muffin fan on the back end of the motor is a good cooling option, especially if coupled with a temp sensor, so it will run on after shut down to cool it.
I've been there and done this on motors up to 75 hp, this was not the first. Three phase motors are dirt cheap anywhere, and mostly they were removed because they need new bearings, and are still electrically sound.
I needed a 3 hp 1800 rpm motor to turn the mill with the VFD, and I used a 5 hp… because I can.Now, no problems.
October 16, 2011
Okay, after much deliberation I am sold on the 1800 RPM motor. My lathe is kind of an odd one and the jack shaft is needed so I can flood cool it at a later date. The placement of the motor puts it below the bed way directly behind the chuck and headstock. The carriage travels about a quarter of the way over the motor to meet the tool bit with the front of the chuck jaws. The bed is "solid" with flat ways and no real clearance to put a splash pan between the motor and the carriage (when it is moved up toward the headstock). A jackshaft being much smaller in overall diameter would give me the clearance needed to create a drain pan for the coolant. By moving the motor further away from the lathe and slightly higher keeps it out of the way. Would the slower motor be suitable for this, if I kept the ratio the same?
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