Need Help! How to Increase RPM on PM-25MV (or similar G0704)


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Thread: How to Increase RPM on PM-25MV (or similar G0704)

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    *Registered User* CNCJoseph's Avatar
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    Default How to Increase RPM on PM-25MV (or similar G0704)

    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.

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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    I'm going through this exact same thing right now but my mill is just a different clone (Weiss VM25L). I used Hoss' plans to make the new mounts and bought pulleys from SDP/SI and opened the bores to fit the motor shaft/spindle splines. 48t timing pulley for the motor, 40t for the spindle, so 1.2:1 ratio. With the stock motor (which is apparently 1100w/1.5hp) I'm less than impressed (no discredit to Hoss or anything, I'm just talking about how this motor handles it) with the motor performance at 5000rpm. With the splines being driven it's also considerably louder at max RPM but part of that is due to my motor pulley not being perfectly concentric, which I'm sure is my fault. Anyway, I'm just having trouble taking any decent cuts with this setup without chatter and yet I see posts from years ago with people taking wayyy more aggressive cuts with excellent finishes, so I'm looking for a new motor myself.

    Unfortunately I don't have 220v in my garage so I'm already pretty limited. On top of that my only experience with VFD's is one of those cheap Huanyang ones used on router spindles and that was awful. I'd just like to find a nice torque spec'd motor on 110 that I can use a 1:1 ratio and control it with my CNC board.

    I'll follow along with your thread so maybe I can find an answer I'm looking for too.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Quote Originally Posted by CNCJoseph View Post
    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.
    Have you considered taking the pulley off the spindle and turning the 60mm down smaller for now?
    Won't be a massive increase, say an extra 1000rpm maybe but it'll do for now until you decide which route you finally take.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Steelcogs, thanks for your input. I'm glad to know I'm not the only one struggling to figure this out right now. From what I have seen out there, timing pulley type setups typically have less than optimal results since they introduce a lot of noise and vibration. Those are never a good thing when you're trying to get the best surface finish possible. However, timing pulleys are still a significant upgrade from the plastic gears on the G0704. The PM-25MV has a Micro-V belt which makes it very quiet machine. It's one of the main reasons I chose it over the G0704. That and the fact I don't have to worry about gears stripping.

    As for voltage, for the longest time I saw installing a 220v outlet in my shop as a hassle. But honestly, in the grand scheme of things, it isn't that much work and expense compared to what I already have invested (and will continue to invest) in my shop setup. I plan to install one within a week or two when my dad is in town since he has a lot of experience in that area. I think it is unlikely that I'll look back and ask myself why I ever bothered to install a 220v outlet. I definitely think it is possible that I could look back and ask myself why I never just went for a 220v setup. I also have a theory that the larger 1.5 or 2.0 HP motor adds more mass to the head which helps absorb / dampen vibration. That may have been a big reason for the aggressive cuts with excellent finish you were referring too. I've heard some people warn about loading down the Z axis too much with a heavier motor. However the conversion kit I used on my machine has the larger NEMA 34 motor on the Z axis so I have plenty of power to raise a heaver 1.5 HP motor instead of the 1.0 HP stock motor which only weighs 7.3 lb.

    PM-25MV CNC Conversion Kit with NEMA 34 on Z

    The Leeson C80T34FZ18 motor I liked to in the first post weighs 30 lb. I guess we'll have to just see what happens if I go this route.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Quote Originally Posted by dazp1976 View Post
    Have you considered taking the pulley off the spindle and turning the 60mm down smaller for now?
    Won't be a massive increase, say an extra 1000rpm maybe but it'll do for now until you decide which route you finally take.
    dazp1976, that is a very unique idea and one I never considered. I just went out to the shop, pulled the spindle pulley and measured things up. The spindle pulley has a 45 mm ID on the 1:1 ratio (max speed). The bottom of the V-grove channels on the spindle pulley has an OD of 58 mm. That means the wall thickness of the spindle pulley is 6.5 mm. However, there is a key that protrudes 3 mm into the ID wall of the spindle pulley meaning you can only machine the spindle pulley OD down 7 mm before you hit the key. Just to be safe you would probably machine the OD down 5 mm. That would give you a 60 to 55 pulley setup which would increase your max RPM from 2500 to 2727. I'll try and insert an image of the spindle pulley below:

    IHow to Increase RPM on PM-25MV (or similar G0704)-cncelements-spindle-pulley-jpg



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    I converted my Sieg X3 (similar to the G0704) to a DMM DYN4 1.8kw servo motor and drive. I used a toothed belt with a 1.8:1 ratio to get 5400 spindle RPM from the motor's 3000 RPM max. It is quieter than he stock setup probably because the power no longer goes through the gearbox. I get excellent finishes on aluminum and Delrin. My goal was more speed but not crazy and the ability to do ridged tapping. Both of which I achieved. I might add a high-speed auxiliary spindle for circuit board milling in the future. Here is a link to my post build thread. https://www.cnczone.com/forums/x3-sx...-software.html

    John



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Quote Originally Posted by rcheli View Post
    I converted my Sieg X3 (similar to the G0704) to a DMM DYN4 1.8kw servo motor and drive. I used a toothed belt with a 1.8:1 ratio to get 5400 spindle RPM from the motor's 3000 RPM max. It is quieter than he stock setup probably because the power no longer goes through the gearbox. I get excellent finishes on aluminum and Delrin. My goal was more speed but not crazy and the ability to do ridged tapping. Both of which I achieved. I might add a high-speed auxiliary spindle for circuit board milling in the future. Here is a link to my post build thread. https://www.cnczone.com/forums/x3-sx...-software.html

    John
    John,

    Wow! What an impressive conversion project! I will definitely need to take a closer look at using an AC Servo Motor as a spindle motor. I love the fact that I don't need to develop / build a separate "encoder kit" since rigid tapping is on my future projects list. Maybe I missed it, what driver did you use for the DST 1.8kW AC Servo Motor spindle motor?



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Quote Originally Posted by rcheli View Post
    I converted my Sieg X3 (similar to the G0704) to a DMM DYN4 1.8kw servo motor and drive. I used a toothed belt with a 1.8:1 ratio to get 5400 spindle RPM from the motor's 3000 RPM max. It is quieter than he stock setup probably because the power no longer goes through the gearbox. I get excellent finishes on aluminum and Delrin. My goal was more speed but not crazy and the ability to do ridged tapping. Both of which I achieved. I might add a high-speed auxiliary spindle for circuit board milling in the future. Here is a link to my post build thread. https://www.cnczone.com/forums/x3-sx...-software.html

    John
    How heavy of a cut can you take with that servo spindle? I've seen plenty of mention of those things but think this is the first I've actually seen mounted. It's got a nice price tag on it so I'm sure it must be nice, especially being able to rigid tap.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    I think one of the heaviest cuts in 6061 aluminum I've take was a 1/2 inch flat endmill 20 in/min, .1" doc, .2" load. I tend not to push for aggressive cuts. This cut was not problem. Even after the gear-up to get a higher spindle speed I still have 1.4HP at the spindle.



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    I was going to speed up my PM-25 too.

    I just wanted to get a quick 3 or 4k I ran into the keyway problem too. That shaft is so large because they put the quill return spring in it. I think they also have a really large ball bearing at the top. That bearing is not going to like 10k.

    You said you wanted more RPM and want 1.5 HP but did not say what size cutters you might be running. RPM's do suck HP so the stock motor may not work.

    To get to 4K with the stock motor you could re make the spindle pulley without the key at the top part so you could make the pulley smaller. The motor mount is one piece and does not really have room for a larger pulley so it would have to go. A new motor mount will let you run a nice large pulley for higher speeds but not 8k.


    I'm lucky because I have a new PM-30 and it has a nice 1.5 HP motor which I'm going to replace with a 2HP 56C motor and a VFD so the old 30 motor will go on the PM-25. Even with that I don't plan on spinning over 6K

    There is a few small frame three phase motors but they are really hard to find. You might ask Matt how much for a 30 motor and a controller. Its a nice upgrade.

    Just for fun.



    youtube videos of the G0704 under the name arizonavideo99


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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    I'm in the same boat. I considered some of the cheap chinese servos for the spindle but eventually decided not - 1.5hp is generally limited to 3000 rpm anyway. I considered turning the pulley down on my lathe but ran into the same problem as Dave. Enlarging the motor pulley is fine, but requires a new mount. It's not like we have the tools to do that is it?



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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    Quote Originally Posted by arizonavideo View Post
    I was going to speed up my PM-25 too.

    I just wanted to get a quick 3 or 4k I ran into the keyway problem too. That shaft is so large because they put the quill return spring in it. I think they also have a really large ball bearing at the top. That bearing is not going to like 10k.

    You said you wanted more RPM and want 1.5 HP but did not say what size cutters you might be running. RPM's do suck HP so the stock motor may not work.

    To get to 4K with the stock motor you could re make the spindle pulley without the key at the top part so you could make the pulley smaller. The motor mount is one piece and does not really have room for a larger pulley so it would have to go. A new motor mount will let you run a nice large pulley for higher speeds but not 8k.


    I'm lucky because I have a new PM-30 and it has a nice 1.5 HP motor which I'm going to replace with a 2HP 56C motor and a VFD so the old 30 motor will go on the PM-25. Even with that I don't plan on spinning over 6K

    There is a few small frame three phase motors but they are really hard to find. You might ask Matt how much for a 30 motor and a controller. Its a nice upgrade.
    ArizonaVideo,

    Thanks so much for sharing your experience. The PM-30 would be a very nice upgrade. I'll probably get a 2HP VFD for my PM-25 so I can easily upgrade to a larger machine / motor in the future. What 2HP motor are you currently considering for you PM-30?

    I watched the video you linked. That was very impressive taking a 3600 RPM motor to 9000 RPM. Although, I see you mentioned in the video description that 7000 RPM was probably a safer speed. Do you think I'll destroy a 1.5HP LEESON 3600RPM motor at 7000 RPM? The manufacturer is saying not to take it above 75 Hz (~4500 RPM), but I'm wondering if they have to say that for warranty purposes. Thoughts? If anyone else has experience running 3600 RPM 3-phase motors at double their rated speed (or more), please share as this is probably the route I am going to take.

    As for your question on cutters. I typically 2D adaptive/contour with no larger than a 1/2" end mill, slot with no larger than a 1/4" end mill, and face with no larger than a 3" fly cutter.



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