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    Default Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by adam_m View Post
    Just out of curiosity @Spumco, what type of collet does your system use and what does your belt drive setup look like on your CNC?

    It seems to me that there are a lot of users trying to get the best of both worlds with spindles running them at 18k and also wanting to run them at lower speeds for machining metal. A servo with 7k RPM and lot's of torque seems to be a good fit just curios why I haven't heard of other users trying to use a similar setup.

    Adam,

    My spindle is a pretty standard 80mm 4-bearing cartridge with R8 taper. . The difference with mine vs. a Tormach or similar is that it was designed from the get-go with an internal (to the head) HTD5M belt and not a step pulley V-belt. Uses 20mm wide HTD belt, single speed. Motor output pulley and spindle pulley are inside the head.

    I'm using the TTS system for tool holders, with a homemade bellville-stack drawbar. You can scroll up for the external view.

    Just guessing here, but I think the reason hobby folks aren't using dedicated 7kRPM spindle servos and drives is that they're staggeringly expensive compared to the cost of a nice hobby-grade mill. So:

    1. Cost. Checking ebay for a 2.2/3.7kW spindle servo and matching drive that isn't covered in industrial goo and has no broken connectors - looking at north of $4k unless you find a screaming deal. My research indicates that dedicated spindle servos have built-in fans and either resolvers or encoders with lower-than normal pulse count so as not to overload the drive inputs when spinning at max RPM. Could be wrong, but I think the spindle motors don't need the super-precise positioning capability of the typical axis servo, but they do need to run all day long.

    2. Availability. There's very little available in the 2hp+ high-speed servo world that can be powered by 230v-1p power. And if you've got 100A 3p power, why are you messing around with a hobby mill? Pour a new pad and buy a VMC.

    3. Complication. Resolvers vs. encoders, trying to match motor/drives from different manufacturers, digging up mostly obsolete data sheets and then deciphering them is challenging. This forum and others are littered with questions about trying to figure out servo drives and motors - I've read hundreds of them over the past year.

    4. Mechanical complexity. Some industrial mills use a 2-speed automatic belt drive and a narrower speed range motor. I can't imagine trying to design or retrofit an automatic speed changer to a mill, then programming the controller to do the speed change based on nothing more than an S-word input and M3/M4 command. Well, I can imagine it, but I can also imagine what a winning lottery ticket or world peace looks like, too.

    The only thing I've found that's close to a (sort-of) affordable turn-key solution is from a couple of the Chinese motor companies who will sell a1.5 or 2.2kW 220-1p 6/8/10kRPM dedicated spindle servo with matching drive for about $1200 delivered. Specs look promising, but neither of the companies I've contacted will send me the drive manuals before purchase. That's a show-stopper, especially since the typical service & return policies are a little... suboptimal.

    So I'm looking for a servo drive that works with 230-1p, has a speed mode with 0-10v input, and is new enough that I can still find a replacement in a couple of years when/if it blows up. Then I find the biggest high-speed servo with an encoder the drive can handle that still fits the physical constraints of my mill.

    I could pull the trigger tonight and have a Parker GV-U12 drive and an N0924-HK servo delivered for about $700-800 from ebay. Cables maybe another $100-200. Add an external cooling fan and try not to let the smoke out.

    Just not quite ready to drop that dime this minute.

    -Ralph



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    Default Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by spumco View Post
    My spindle is a pretty standard 80mm 4-bearing cartridge with R8 taper. . The difference with mine vs. a Tormach or similar is that it was designed from the get-go with an internal (to the head) HTD5M belt and not a step pulley V-belt. Uses 20mm wide HTD belt, single speed. Motor output pulley and spindle pulley are inside the head.

    I'm using the TTS system for tool holders, with a homemade bellville-stack drawbar. You can scroll up for the external view.

    Just guessing here, but I think the reason hobby folks aren't using dedicated 7kRPM spindle servos and drives is that they're staggeringly expensive compared to the cost of a nice hobby-grade mill. So:

    1. Cost. Checking ebay for a 2.2/3.7kW spindle servo and matching drive that isn't covered in industrial goo and has no broken connectors - looking at north of $4k unless you find a screaming deal. My research indicates that dedicated spindle servos have built-in fans and either resolvers or encoders with lower-than normal pulse count so as not to overload the drive inputs when spinning at max RPM. Could be wrong, but I think the spindle motors don't need the super-precise positioning capability of the typical axis servo, but they do need to run all day long.

    2. Availability. There's very little available in the 2hp+ high-speed servo world that can be powered by 230v-1p power. And if you've got 100A 3p power, why are you messing around with a hobby mill? Pour a new pad and buy a VMC.

    3. Complication. Resolvers vs. encoders, trying to match motor/drives from different manufacturers, digging up mostly obsolete data sheets and then deciphering them is challenging. This forum and others are littered with questions about trying to figure out servo drives and motors - I've read hundreds of them over the past year.

    4. Mechanical complexity. Some industrial mills use a 2-speed automatic belt drive and a narrower speed range motor. I can't imagine trying to design or retrofit an automatic speed changer to a mill, then programming the controller to do the speed change based on nothing more than an S-word input and M3/M4 command. Well, I can imagine it, but I can also imagine what a winning lottery ticket or world peace looks like, too.

    The only thing I've found that's close to a (sort-of) affordable turn-key solution is from a couple of the Chinese motor companies who will sell a1.5 or 2.2kW 220-1p 6/8/10kRPM dedicated spindle servo with matching drive for about $1200 delivered. Specs look promising, but neither of the companies I've contacted will send me the drive manuals before purchase. That's a show-stopper, especially since the typical service & return policies are a little... suboptimal.

    So I'm looking for a servo drive that works with 230-1p, has a speed mode with 0-10v input, and is new enough that I can still find a replacement in a couple of years when/if it blows up. Then I find the biggest high-speed servo with an encoder the drive can handle that still fits the physical constraints of my mill.

    I could pull the trigger tonight and have a Parker GV-U12 drive and an N0924-HK servo delivered for about $700-800 from ebay. Cables maybe another $100-200. Add an external cooling fan and try not to let the smoke out.

    Just not quite ready to drop that dime this minute.

    -Ralph
    Thanks for clarifying and the detail.

    I now see why the hobbyist isn't taking on this project due to the cost impact.

    Adam,

    G540, Rack and Pinion Drives-X/Y axis, 1/2-Ball Screw-Z Axis w/THK HSR 25 Linear Slides, Steppers KL23H2100-35-4B, Power Supply-KL-600-48


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    Default Re: New spindle motor - Servo or Induction?

    There are folks who have done it, of course. Youtube has some videos, and there are threads on this board concerning successful servo spindles. I've only seen a couple, however, where it's obvious that the person who did it dropped some major coin. Most of them look like what I'm trying to do - find a used drive/motor on the cheap and get it working.

    You're mostly right - it's about a 1000:1 ratio of "Help me get my induction/treadmill/router spindle sorted out" to "Check out my working industrial servo spindle."



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    Default Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by spumco View Post
    .So here's the next question: The Parker servos - and other Mfgrs I assume - generally have two flavors of servo in each frame & stack length. One is a low inertia, and the other is high. In the case of the Parker that would be N0924 and J0924.

    For a spindle application, which would be preferable - high or low inertia? And why - 'cause I'd like to understand this a bit better.

    Thanks again for everyone's input.

    -Ralph
    That is a really good question and I had to do a bit of research to see the difference. The low inertia motors generally have lower max torque and higher max RPM.

    Here is the specs on two motors from Automation Direct

    SVL-210
    Power 1KW
    Rated torque, N-m 3.3
    Max torque, N-m 9.9
    Rated speed, RPM 3000
    Max speed, RPM 4500

    SVM-210
    Power 1KW
    Rated torque, N-m 4.8
    Max torque, N-m 15.7
    Rated speed, RPM 2000
    Max speed, RPM 3000

    So the bottom line is that you are trading torque for speed, so a sports car vs. a truck. The only way to increase both torque and speed is to spend more $$

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: New spindle motor - Servo or Induction?

    The low inertia motors generally have lower max torque and higher max RPM
    Not that I really understand the inplications, but I'm finding that to not be universal among servo manufacturers. I think it is utterly dependent on how they wind it and add other sercret sauce.

    For example, according to the Parker datasheet for then N0924 vs. J0924 all the specifications are the same - the only difference is the rotor inertia. Parker's brochure on the Neometric:

    The J Series motors provide the same performance as the NeoMetric Series, but feature a higher rotor
    inertia.


    Same thing for the newer MPP/MPJ series of motors. Same amps, torque, etc. Just the inertia is different.


    On the other hand, other manufacturers do change the electrial characteristics in addition to the mechanicals. Baldor's BSM series have a BMSxxN or BSMxxC (low vs. high inertia).

    I'm not sure I'm comparing apples to apples, but here's the data:

    BSM90N-375
    Continuous stall torque lb-in 117
    Continuous current amps 19.01
    Peak torque lb-in 471
    Peak current amps 68.47
    Rated speed @ 300 volts rpm 4000
    Inertia lb-in-s2 0.0082
    Maximum speed rpm 7,000
    Number of motor poles — 8
    "Peak torques are four times continuous. This series has the lowestinertia to provide the maximum torque per package size."

    BSM90C-375
    Continuous stall torque lb-in 69
    Continuous current amps 12
    Peak torque lb-in 207.1
    Peak current amps 30.8
    Rated speed @ 300 volts rpm 4000
    Inertia lb-in-s2 0.0117
    Maximum speed rpm 7,000
    Number of motor poles — 8
    "Peak torques are typically three times continuous."


    The only thing I've been able to glean from multiple mfgr brochures is that one would select a servo to minimize the inertial mismatch between the rotor and the load being driven. In the case of a pick and place machine, I think a low-inertia servo is preferred. In the case of a Y-axis mill motor (moving the X and the saddle), a high-inertia motor is the way to go.

    So I'm thinking for a spindle application that either is fine, but high-inertia servo might be better due to the rotational inertial of the spindle & tools at high RPM.

    Thoughts?

    -Ralph



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    Default Re: New spindle motor - Servo or Induction?

    OK, I'm confused

    If the max speed is the same, I would go for the higher torque. I don't think the rotor inertia is really going to be a factor for a spindle.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by Jim Dawson View Post
    OK, I'm confused

    Me too.

    Looking over the Misubishi spindle servo site and I'm overwhelmed.

    I've come to the conclusion that I'm going to go for whichever is cheaper, given a choice between low or high inertia motors of equivalent size/amps/speed.



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    Default Re: New spindle motor - Servo or Induction?

    Generally the higher inertia motors have more torque and lower speed (and are fatter, but not as long) as the low inertia versions. The Baldor motors are named by frame size, so you're comparing a 120mm low inertia to a 120mm high inertia motor. The low inertia is a larger, more powerful motor.



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    Default Re: New spindle motor - Servo or Induction?

    This has potential. Half the weight, runs off my current VFD. Sadly, no torque curves and a max RPM from the MFGR of 4140RPM. Meaning I'd want a 2:1 pulley unless I decide to flog it to 120hz.

    https://www.techtopind.com/motors/CB3-AL-TF-56HC-2-B-D-3




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    Default Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by spumco View Post
    This has potential. Half the weight, runs off my current VFD. Sadly, no torque curves and a max RPM from the MFGR of 4140RPM. Meaning I'd want a 2:1 pulley unless I decide to flog it to 120hz.

    https://www.techtopind.com/motors/CB3-AL-TF-56HC-2-B-D-3

    that motor at nameplate volts/hz will develop 3hp worth of torque at 3600 rpm, which is 4.5 foot pounds while consuming nameplate amps.

    keeping the amps constant at 8 the torque will be flat from 0rpm to 3600 rpm. you can estimate the peak torque you have available from the ratio of 11 amps (the max your vfd can deliver) and the 8 amps the motor draws at full load. at 11 amps the motor will internally produce 1.9 times the heat it was designed for, so keep that in mind with regard to temperature rise.

    above 3600 rpm the torque drops off according to the ratio of the square of the voltage same as any induction motor. so at 7200 rpm your motor wants 480vac/120hz, but the vfd can only deliver 230vac/120hz. so the torque it will produce at the same slip, is one fourth of nameplate. but the rpm is double, so I see no reason why you can't get 1.5 hp from that motor, with the vfd you have, at 7200 rpm. so a 1:1 belt ratio should work for you.

    however in order to get the torque you need for rigid tapping 1/2-13 you may need to run a 1.3:1 belt ratio which means 10,000 rpm for a 7500 rpm spindle.

    Last edited by Eldon_Joh; 08-22-2018 at 09:32 PM.


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    Default Re: New spindle motor - Servo or Induction?

    I'm thinking I need to give up on rigid tapping 1/2-13 in steel and settle for a spindle/motor/pulley arrangement that falls on it's face below 1kRPM but works well up to 7 or 8kRPM.



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    Default Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by spumco View Post
    I'm thinking I need to give up on rigid tapping 1/2-13 in steel and settle for a spindle/motor/pulley arrangement that falls on it's face below 1kRPM but works well up to 7 or 8kRPM.
    i tend to agree or you need to figure out how to change the pulley ratio during a program.

    if you want to get more performance from an even smaller 2 hp motor, wire it for 140 volts and drive it from a 5HP vfd. at a 1:1 belt ratio you *might* have the torque to rigid tap (but the motor will overheat if you do a lot of holes, since you'll be operating it at double its rated torque) and you'll have 3 hp worth of power without overloading the motor at around 5000 rpm. if you can run the motor out to 10,000 rpm then a 1.3:1 ratio will help out with rigid tapping.

    at low speed during tapping the vfd will not actually be consuming that much power from the line (less than 2hp) (but it will be sending 15+ amps into the motor) so you're safe to run the 5hp vfd from single phase.



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    Default Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by Eldon_Joh View Post

    if you can run the motor out to 10,000 rpm then a 1.3:1 ratio will help out with rigid tapping.
    .

    I'd like to see that motor run at 10,000 RPM.......... From a safe distance. I wonder if the case would contain the exploding armature? That would be one of those ''Hey you guys, watch this'' moments.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: New spindle motor - Servo or Induction?

    Not that I don't appreciate the advice, but I was thinking the same thing.

    "Hold my beer for a minute..."

    Sort like in the old days when we used to run a pool on how long it took for a air-cooled VW block to burn through the asphalt.

    Back to looking for cheap servos...



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    Community Moderator Jim Dawson's Avatar
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    Default Re: New spindle motor - Servo or Induction?



    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: New spindle motor - Servo or Induction?

    i see no problem with it provided you balance the rotor properly. 3600 rpm synchronous generators are manufactured on the order of 40 feet long, 5 foot diameter. they run past the first critical speed of the generator.

    its not like the aluminum is going to fly out of the rotor..though that can happen when you overload the motor to the point the aluminum melts.



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    Default Re: New spindle motor - Servo or Induction?

    Good point.

    I'm looking more for an 'off-the-shelf' solution that will be reasonably easy to replace in the future. Buying a motor and then paying someone to tear it down and balance it - or re-wire it - isn't really in the cards. I have enough figurin' to do with mounting the motor and then coming up with a PDB.



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    Default Re: New spindle motor - Servo or Induction?

    Another option may be a 200hz (12k RPM) spindle. A Turkish spindle manufacturer makes 100, 200, 300 and 400hz spindles. 200hz spindle sounds good the me for the job because 1:2 pulley makes it 6k RPM and some torque will be added. Back side mounting is a problem though.

    ARFM 2Y

    Last edited by Azalin; 08-23-2018 at 12:50 PM.
    Suat
    Proud father, C# developer, Model heli pilot, newbie free time machinist for hobby


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    Default Re: New spindle motor - Servo or Induction?

    Currently looking for exactly the same thing.
    There are a couple of VFD's that can run PMAC motors & servo's. But finding the correct duty motor is not easy.
    Azalin,
    On the Arel page there is a motor listed as an ARFM.2K-L3 that looks promising at 1:2 pulley ratio (18000 rpm to 9000 at spindle at 300Hz)
    However there are no performance curves or drawings for this. Have you seen them also what do they generally sell for.
    Regards,
    Michael



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    Default Re: New spindle motor - Servo or Induction?

    These are basically router spindles.

    9000 rpm is too fast for my spindle but 6000 is ok so it is 200hz.

    I'm too concerning about the torque at low speed. I'll call them and ask for a datasheet if they have.


    Sent from my MI 5s Plus using Tapatalk

    Suat
    Proud father, C# developer, Model heli pilot, newbie free time machinist for hobby


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