Reply To: vfd question

[Anonymous]

Posted by Maurice Taylor on 22/03/2020 20:36:11:

I enjoy reading all the posts on VFD,s and 3 phase motors etc. Do these produce better quality work than a single phase motor with gearbox or belt/pulleys

In theory a 3-phase motor is smoother than a single phase one as the rotating magnetic field in a 3-phase motor is of constant amplitude whereas in a single phase motor it pulsates. They also provide easy speed changing and useful features such as controlled ramp up and down and quick stopping if a braking resistor is used, They can also be used to jog the spindle which is helpful for tapping or using a die to cut threads. It also depends on how big a PITA belt changing is on a particular machine. That's not an issue for me as all my manual machines are gear driven, except the Bridgeport which is a varispeed belt, so just twiddle the handle.

On the downside at slow speeds the power is reduced as the torque stays constant rather than being multiplied up as with belts or gears.

From a manufacturers viewpoint they allow one to get rid of belts and/or gearboxes which are expensive to provide; an important point when customer purchases are made on the basis of cost rather than performance.

There is an argument that belts and gears can cause vibration that marks the work. Some toolroom lathe manufacturers went to great lengths to isolate the belt/gear speed changing from the spindle itself.

In principle VFDs are pretty straightforward, but you do need a fair degree of knowledge to set one up and to understand the manuals. Whereas belts and gears are dead simple.

Andrew