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

  1. #49
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    Default Re: How to Increase RPM on PM-25MV (or similar G0704)

    I've been flipping between the two ideas for a while now. I think I understand the relationship between ultimate motor torque and RPM now. Basically, the diameter of the motors with high torque is larger and they can't spin fast enough. I have a friend who balances turbochargers to 150k RPM, so it could be an option to use one of his balancers and try to balance the guts of a motor if it vibrates too much. I'm really liking the Leeson experience and leaning that way.

    Need to finish up the actual CnC kit first. Does anyone know if a kit can be bought that doesn't require you to buy all the parts? IE ballscrews and motor mounts are a waste of time for me. Also, I wonder if a spindle upgrade like this would conflict with the Z-Axis?



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

    Quote Originally Posted by hackish View Post
    I've been flipping between the two ideas for a while now. I think I understand the relationship between ultimate motor torque and RPM now. Basically, the diameter of the motors with high torque is larger and they can't spin fast enough. I have a friend who balances turbochargers to 150k RPM, so it could be an option to use one of his balancers and try to balance the guts of a motor if it vibrates too much. I'm really liking the Leeson experience and leaning that way.

    Need to finish up the actual CnC kit first. Does anyone know if a kit can be bought that doesn't require you to buy all the parts? IE ballscrews and motor mounts are a waste of time for me. Also, I wonder if a spindle upgrade like this would conflict with the Z-Axis?
    I don't know of anybody that sells partial kits. Try reaching out to the guys who make conversion kits and asking them.

    However, if you already have ballscrews and motor mounts, it might be quicker and easier to finish the conversion yourself. You could simply use long standoffs to mount the stepper motors. If you don't have a lathe to make your own standoffs, McMaster sells them in various sizes and materials. You may have to stack different sizes to get room for the coupler between the stepper motor and ballscrew.

    So far I'm really glad I went the Leeson motor route. My motor arrived last night and I was able to get the face plates swapped out without any trouble. I'll post pictures later today when I have more time. From what I've heard, these Leeson motors wont' vibrate much, even at 10k rpm. Your biggest source of vibration will probably be your spindle and pulleys. Since both pulleys are made from aluminum, the two steel grub screws that are used to secure them to the shaft throws them off balance. Even if the spindle was perfectly machined, there's also a grub screw in the spindle that keeps the collet from rotating which throws the spindle off balance. All of these components would have to be dynamically balanced separately. I have actually toyed around with the idea of making my own dynamic ballancer for other projects. When I was a student at school, we had a dynamic ballancer in our engineering lab that we had to master to pass our vibrations course. That was more than ten years ago, but I think I still remember the key concepts.

    But, now you've given me a new idea to add more scope to my project I should mount an accelerator at specific points on my machine and take readings at specific RPM. I can then compare the differences in vibrations at the same points before and after the conversion at those same RPM. Should be an interesting experiment.

    From the preliminary measuring and CAD work I've done, I don't foresee any issues with clearing the Z axis stepper motor. You'll be able to see for yourself as this project progresses. Just keep in mind I have at least a dozen other projects in work so it might take a while.

    Last edited by CNCJoseph; 11-20-2018 at 11:16 AM.


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

    CnCJoesph, I have many of the components and the difficulty is that the kits are always made for NEMA standard size motors and my servos are metric panasonic units. The mounts are done and I have the dual nuts and screws. The problem is the end caps and ball screw mounts. These parts all need an assembled mill to make, and are the least difficult and expensive to produce. I don't know if manufacturers think I'm going to go into production and thus won't sell simple parts - they seldom even respond. It's the hours of messing about with bearings, shims and mounts that I would prefer to avoid.

    With respect to the pulleys, put 2 or 3 screws in at equal angles. I do think the slot milled out of the spindle shaft will cause an imbalance, but maybe someone could just mill the same size out 180 degrees. I've looked at the PM25 head a few times and wondered how feasable it would be to produce an entirely new unit. Converted to CnC, we don't need the quill, and with a VFD, a lot of hardware gets removed. I've even seen replacement cartridges the support bt30 type holders.

    Last edited by hackish; 11-20-2018 at 01:02 PM.


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

    I think the Tormach 1100 (series 3) is a 4-pole motor that can go to around 4500 RPM and then like a 1.2:1 pulley in top range.
    On TEFC motors, the fan will consume a lot more power as you increase the RPM (square law I think.) Also, it may want to explode at higher RPM's. Other limitations to high RPM's are the motor bearings and balancing of the rotor.
    So just because 1 motor can do 6000 RPM, doesn't mean another can.



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

    Quote Originally Posted by skrubol View Post
    On TEFC motors, the fan will consume a lot more power as you increase the RPM (square law I think.)
    I think on a 1.5hp motor, the frictional losses of turning a 5" fan through air will not be a big enough loss to worry about.



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

    Quote Originally Posted by hackish View Post
    I've looked at the PM25 head a few times and wondered how feasable it would be to produce an entirely new unit. Converted to CnC, we don't need the quill, and with a VFD, a lot of hardware gets removed. I've even seen replacement cartridges the support bt30 type holders.
    I would be a huge fan of a BT30 holder on my machine. Let me know if you ever explore this path further. One concern I have about upgrading to 1.5 HP is the TTS style tool holders pulling out with my favorite 1/2" carbide cutters. I've had it happen before with the stock motor. It left an ugly mark on my hardened vice jaws and destroyed the $80 cutter. In hindsight, I wasn't being as careful as I should to make sure oil never gets on the TTS collet or tools.



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

    I really think cast iron would be the best material, and the head itself doesn't seem like it would be terribly expensive or complicated to have cast. Many years ago I had some prototypes cast (of AL) and they came out to under $100 each. Even if I dropped $250 on a rough casting for a new head I could machine and subsequently install a BT30 cartridge in, it is probably something I'd do. Of course not that I love machining cast iron. Ugh.



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    *Registered User* CNCJoseph's Avatar
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    I wanted to close the loop on my spindle motor upgrade for anyone else who decided to tackle this project. First of all, thanks so much to everyone who shared their insight and experience with this project. It was all very much appreciated.

    This is the motor and VFD I ended up using:

    1.5 HP Leeson 3600 RPM electric motor $275
    DURApulse GS3-22P0 VFD $293

    I now have more than enough horse power for anything I throw at my PM-25MV. I can also operate at up to 6000 rpm, but I would say the machine is happiest at up to 5000 rpm. I was hoping for 7500 rpm, but the spindle starts to vibrate too much above 5000 rpm.

    As far as the setup goes. The motor fits just fine using the stock pulleys and belt. All I had to do was machine a new motor mount and bore out the motor pulley on my lathe to fit over the end of the larger Leeson motor shaft.

    What I love about this upgrade:
    1. No need to change the belt to the 1:2 speed ratio since the motor has plenty of pour. I have even tapped 22 mm holes with the new setup using the 1:1 speed ration.
    2. The VFD controlled spindle speed and direction is extremely easy to control via Centroid Acorn / pendant.
    3. Tapping is really easy since I can reduce the spindle speed to 120 RPM.
    4. I have more HP than I know what to do with.
    5. I have more than doubled my spindle speed.
    6. I can now machine parts ~20% faster.

    What I don't love about this upgrade:
    1. I had to upgrade the spindle bearings to AC bearings. The runout is three times worse with the new bearings. I even tried replacing the bearings thinking I got a bad set. Same issue, and these are the same bearings everyone uses to upgrade their spindle bearings. Replacing these bearings is a pain.
    2. I'm having issues with large diameter (1/2"+) end cutters pulling out. I currently use Tormach's TTS. Iv'e tried thoroughly cleaning the inside of my spindle, R8 collet, tool holders, etc. Still have issues, even when manually clamping down the drawbar with wrenches.
    3. Chips are being ejected out the top of my enclosure even though my enclosure has 5 ft high walls. I need to make a roof for my enclosure.
    4. To fully realize the ability of my upgraded drive system, I should probably upgrade to flood coolant.
    5. This project gets very expensive very fast. By the time you factor in line filters, proper VFD motor cable, upgrading your shop with a 220V outlet, upgrading your control box with new circuit breakers, adding a contactor connected to E-stop to remove power to your VFD (highly recommended), etc. You're easily talking at least $1500.

    As far as productivity, I can now run the same parts 20% faster than I did before the upgrade. Roughing is where you'll see the biggest improvement in speed. However, for the best finishing cuts, I still find myself running at lower feeds and speeds similar to what I used before the upgrade.

    Would I recommend you do this upgrade to your machine? If you are contemplating this upgrade as a hobbyist, it is definitely a fun and challenging project, however, I think there are some other projects I would cross off my list first. Definitely don't consider this project unless you already have a full enclosure (not just sides but roof as well) and possible flood coolant as well. You'll love how easy it is to control the VFD using your CNC control board. If you're contemplating this upgrade to improve productivity to manufacture and sell parts on the side, you're probably looking at a 20% increase in production capability. I would definitely first have an enclosure. You might want to invest in a power drawbar first. That's where you'll probably see the biggest improvement in productivity, particularly on complex parts where you have to do many tool changes.



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

    Just throwing out an option here. (Not that I'm in a position to try this myself).

    Similar to the DMM servos that rcheli mentioned, earlier in this thread, might I suggest as an alternate servo for consideration. TEKNIC.

    For example, check out the CPM-MCVC-N0563P-RLN. A 230 volt, 3-phase servo, rated at 1.8 Kw, putting out a flat torque of 1,147 oz-in across it's entire speed range, all the way up to nearly 2700 rpm.
    As a motor, it has plenty of reserve 'oomf', with peak torque being 4x higher 4,650 oz-in. And it weighs only 25 lb. That's very lightweight.

    Not enough power? the same motor, is offered with a cooling fan and shroud. The CMP-MCVC-N0563A-RLN gets rated at nearly 3Kw (4 hp) continuous, with a respectable increase in it's continuous torque. Weight increases to 27 lb.

    One of the main advantages of TEKNIC motors in general are how easy they are to interface with. For example, they have built in controllers (fully opto-isolated) which can take a PWM signal for speed control.

    Of course, all of this costs. But you can figure in some money saved by not needing a VFD or complicated interface electronics to your controller. Plus, it's nice not having to deal with mounting a bulky servo-controller box near by.

    Unresolved issues: I don't know if this motor, which uses 3-phase, would be happy with a static converter. It might require a rotary converter.

    I have no association with TEKNIC. This is just me, dreaming a big 'what if'. So, that's all I have to offer.



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

    My Setup on my G0704 is a Allen Bradley MPL-A330P-SJ22AA motor on an Ultra 3000 servo drive. 5000rpm at the servo, 1:1 belt drive to the spindle through GT3 curvilinear timing pulleys and a nylon fabric faced belt. I get constant torque up to 2800 rpm and full HP up to 5000 rpm (the torque drop off is minimal, maybe 20%?). Noise level is low, even at 5000 rpm (73 dBA) and the 1:1 gearing should make rigid tapping easy. 1.8kW (2.3HP)



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

    Hi! I read the all thread and since there are several options I would like to ask whether there is a more straight forward modification to speed up the spindle. Like a gear change to 1:1 (my motor is rated for 5600rpm) or a new motor with more power and rpm, that is compatible and I only have to replace the current one. Thanks for the help! Ah I have a optimum BF20L, basically the same of a G0704 except that I have MT2 spindle and not Mt3 unfortunately ( no TTS tool for MT2 so far :-( )



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