As the Title says I have a BP 2J 1 1/2 head and I am installing a 3 HP VFD. My question is - Which would be better for the machine, to adjust the speed with the VFD or the Vari-Speed head? Thanks
You are best setting the spindle speed with the Vari-speed for several reasons, a mechanical speed reduction system gives you a better mechanical advantage (torque) vs. reducing the motor speed, the other thing is that using the Vari-speed in one position will wear it unevenly more quickly if you just were to use the motor speed control. So general recommendation is use the vari-speed for most of your speed changes but the VFD can be used for smaller speed changes. The Vari-Speed drives wear out and can be expensive to repair, it is not uncommon to put a larger motor on the head 3 or 5 Hp, convert it to a single belt speed with a 1:1 drive and use that with the back gear for low speed. I prefer to use in inverter/vector type motor because they can easily run from 20-200 Hz, so very wide operating range. A larger Hp makes up the power loss when you are running it below the base speed of 60 Hz. I have done and also helped a number of individuals with the conversion.
I generally run my 3 HP Wells Index at about 45-50 Hz, it's a little quieter there. Then I use the machine's original variable speed control for adjusting RPM, unless I need to go slower than the low end of the range (uncommon). I don't worry about the original speed indications being off as I added a digital tach