I have a Precision Mathews PM-25MV and I need help increasing the RPM. I am currently limited to 2500 RPM. I already have high speed bearings that will allow me to take the spindle to 12,000 rpm.However, from what I can tell there is no way to modify the controller to increase the RPM. In fact, it is encased in epoxy. I understand Precision Mathews not wanting anyone to modify the machine and potentially void the 3 year warranty. I voided it a long time back converting it to CNC so I'm not worried about voiding warranty.
For those not familiar with the PM-25MV, it has a 1 hp motor that maxes out with its controller at 2500 RPM. I removed the motor housing, motor, and pulley this morning to take a closer look. It has a Gates Micro-V belt (5 rib) that results in whisper quite operation. The motor shaft is 12 mm dia. The pulley on the motor shaft has a 40 and 60 mm dia pulley. The pulley on the spindle has a 60 and 80 mm dia pully. This results in an either 1-1 ratio (max 2500 rpm) or 2-1 ratio (max 1275 rpm). Side note: I work mostly with aluminum and have never had a need to use the 2-1 ration. I've had no issues tapping 8 mm holes with the 1-1 ratio in 6061 aluminum.
My goal is to have a 1 to 1.5 hp machine that can drive the spindle at 7,500 to 10,000 rpm. Yes, I realize I will need to upgrade the spindle bearings and maybe dynamically balance the spindle. I'll save that for later.
Some options I've considered.
Option 1 - modify the existing control board. From what I understand, the Grizzly G0704 uses a similar 1 HP motor that maxes out with a similar controller at 5,000 RPM. If anyone knows if there is a way to do this, please let me know. I don't mind going this route even if I have to dig through some of the epoxy encasing. I wouldn't be surprised if it is a simple matter of replacing a resistor or adding a jumper. However, this would probably be a temporary solution since I doubt the stock motor is meant to operate above 5,000 RPM for long.
Option 2 - machine a larger pulley for the motor shaft. This would mean having to completely redesign the motor mount to allow for clearance. Even if I machined a 120 mm pulley, I am still going to max out at 5,000 rpm. If I am going to go to the trouble of redesigning the motor mount, I may as well upgrade the motor well I'm at it.
Option 3 - offset the motor and add a second set of pulleys and v-belt with a 4 to 1 ratio that drives the current motor pulley which then drives the spindle. I've seen this done before. This would increase the range to 5,000 or 10,000 depending on how you have the pulleys set up. Again it means completely redesigning the motor mount, and if i am going to take the time to do that, I may as well upgrade the motor well I'm at it.
Option 4 - Get a motor and driver from an old treadmill. This seems a popular option with G0704 CNC conversions. This is probably my lease favorite option
Option 5 - Install a quality motor and VFD. This is the most expensive option, but it is my favorite. I have heard of people doing this to their G0704 but not a PM-25MV. If there is anyone out there that has gone this route with the G0704 or PM-25MV, please chime in. This is currently the hardware I am looking at.
1.5 HP Leeson 3600 RPM electric motor $275
LR-22P0-1PH Input Line Reactor $72
For the VFD, these are some of the options I am looking at:
DURApulse GS3-22P0 $293
1.5 HP Leeson 174651.00 $330
Emerson SKBD200150 $415
According to Meghan, a very helpful sales rep at Electric Motor Wholesale, the Emerson motor has a 20:1 constant torque. She also contacted Emerson directly for me who stated the motor shouldn't be driven at more than 75 Hz (4500 RPM if I did my math right). That is disappointing as I was hoping I could drive it up to 120 Hz (7200 RPM). I'm pretty sure I have seen other people drive comparable Emerson motors at 7200 RPM. Is this just the manufacturer being overly cautions? If you have any experience upgrading your motor on your PM-25MV or G0704, please share tips and advice. Regardless of what I do, I'll continue to update this thread so you can follow along.