I am thinking of buying a 3 phase motor for my PM-835S from Precision Matthews so I can have variable speed without having to keep changing belts on the step pulley. I need a 220v 1 phase input, 220v 3 phase output VFD, something that can reverse directions.
Any recommendations or is that something I should also talk to PM about and order it from them also?
Hi,
From the operators manual for your mill, it looks like it uses a "C" Face motor attached to a mounting ring made specifically for that mill.
The motor should have a number and a letter that indicates which mounting size and configuration it is like: "56C" for example.
If there is no number and letter for the mounting size and type, you can cross reference the measurements with most any motor manufacturer's specs to get the right configuration.
I would suggest buying an "Inverter Duty" motor, they are made specifically for use with AC Drives (VFD).
The advantage of using an inverter duty motor is their ability to run at very slow speeds without overheating.
Non-inverter duty motors tend to get pretty warm at slow speeds because the motor fan doesn't turn fast enough to cool itself.
Dura-Pulse AC Drives from Automation Direct are good drives IMHO, I have installed several of them in industrial plants with good results and they aren't too expensive. I installed a 20 HP Dura Pulse drive about 10 years ago on a non- inverter duty machine and it is still working good, no issues so far. That particular machine never runs at really slow speeds so a non-inverter duty motor was OK in that case.
I suspect you will want to run your mill at very slow speeds from time to time.
You can use an external knob (potentiometer) to control the speed by changing one parameter in the drive, there are several good "How to" videos on YouTube on how to change the parameters for using speed control knobs as well as external start, stop, forward and reverse buttons/switches. (if you need to).
Just my opinion but a 3 phase motor is the only way to go if you want really slow speeds, single phase motors loose nearly all their torque at slow speeds. Just throwing that out there, I realize you weren't entertaining that idea.
BTW, I have found that the Dura Pulse AC Drives come factory set with good torque curves for machine tools, in most cases they don't really need fine tuning, I did have to tune the torque curve and ramp time for a conveyer system once but the factory setting is pretty much setup for machine tools like your mill.
You may wat to adjust the ramp up and ramp down times though, factory settings are something like 6 seconds if memory serves me right.
You probably don't need the a brake resistor (dynamic braking) on the drive since your mill has a manual spindle brake.
You probably could set the pulley system in the high speed setting and leave it, but still use the High Range/Low Range Cam Lever.
Kind of odd that Low Range is from 80 - 325 while High Range is from 660 -2720, nothing in there for speeds between 325 and 660?
An AC Drive would solve that issue
(AKA: VFD, Sorry, I have always called them AC Drives for some reason).
Must be a little annoying that the spindle reverses direction between High Range to Low Range. I would definitely have a hard time getting used to that!
But for the price of that machine, little upgrades and getting used to small quirks would be worth it in the long run.
Almost forgot, most metric motors can be cross referenced to standard NEMA motor frames, the main difference is usually the length and diameter of the output shaft, most other dimensions like the bolt hole circle diameters for mounting will cross reference.
In other words, you should be able to get a standard 56C Face motor (for example) with a metric sized shaft
It may pay to measure the existing shaft diameter, some motors from overseas already have imperial sizes like 1-3/8 thru 1-5/8" for a 3 HP motor.
Anyway, I hope this helps!!
Have a great day!!
Joe
