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IndustryArena Forum > CNC Electronics > Spindles / VFD > New spindle motor - Servo or Induction?
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  1. #21
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    May 2013
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    Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by spumco View Post

    The 56 frame motors are the same as my 145, but I need a face-mount with a removeable (or no) foot. And the cast-iron motor from surplus center is, more or less, what I have right now.
    i thought you implied your motor was 65 pounds when you put that as the upper limit for what you want. not the case?

    anyhow taking a standard 2hp 230 volt motor and rewiring it for 140vac is a reasonable option to get 3 hp from it, using your existing vfd drive.

  2. #22
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    Re: New spindle motor - Servo or Induction?

    My motor is 72 pounds, not including the encoder and shroud (negligible). Anything lighter than that is preferable. The 3HP 56C washdown motor I found on eBay is 65lbs, and the 2HP is about 45lbs. That's kind of the target as those would be the easiest motors to install since the bolt pattern is the same as my current motor.

    But the real issue with my current is motor the outside diameter. The 145TC/56C face dimension fits - but the cast iron motor housing OD is significantly larger than a sheetmetal housing with the same mounting dimensions. The cast iron cooling fins and non-removable base mean the actual OD is closer to the next frame size larger.

    This extra-large OD is what is encroaching close enough to the spindle that an air cylinder or air/hydraulic power drawbar assembly won't fit directly over the spindle.

    A sheetmetal motor in 56C or 145TC might work, but I don't know for certain. I would have pull my motor and make a mockup to see just how close a sheetmetal motor is to the spindle.

    Photo shows the fundamental issue. Even if I moved an oil distribution manifold and shoved the motor back a bit, I'll only gain 0.5"

    This is why I'm thinking 90/100mm servo.


  3. #23
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    Jan 2009
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    23

    Re: New spindle motor - Servo or Induction?

    Eldon Joh,
    Would you mind expanding on what you mean by re-lacing the wires. I assume this is all done within the terminal box, not rewinding the motor.
    Do you get the same torque at lower speeds or does this change.
    Thanks

  4. #24
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    Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by mick41zxr View Post
    Eldon Joh,
    Would you mind expanding on what you mean by re-lacing the wires. I assume this is all done within the terminal box, not rewinding the motor.
    Do you get the same torque at lower speeds or does this change.
    Thanks
    by re-lacing the wires i mean rewrapping the end turns where the wires exit the coils, i cut some of it apart to get to the internal star connection point. like this but by hand.. https://www.youtube.com/watch?v=U1Ef0_F6h6M


    so in your case, you have a 2 hp motor, its line currents are on the order of 5.5 amps. the reason why you can get 200% torque at low speeds is because your vfd can deliver 11 amps. (not for long or you burn up the motor)

    but once your motor exceeds nameplate rpm the torque it can deliver falls because it needs more voltage than the vfd can deliver.

    if you rewire your motor for 140vac, its going to pull about 9.5 amps at full load torque. so with a maximum of 11 amps, you are only going to get a maximum of 1.2 times nameplate torque. However, the motor will be able to deliver nameplate torque all the way up to (240/140) times nameplate rpm. above this it will drop.

    ideally you would change the belt ratio to take advantage of this.

    ----
    i'm reasonably certain as it is now you can't even get 1 hp from your 1800 rpm motor above 3600 rpm at the motor (because at this rpm it needs 480 volts at 120 hz and your vfd can only deliver 240vac.)
    your 1.5 to 1 belt ratio then steps this up to 5400 rpm at the spindle.

    what's the line currents at the motor when you're pushing the spindle that fast typically?

  5. #25
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    Re: New spindle motor - Servo or Induction?

    what's the line currents at the motor when you're pushing the spindle that fast typically?
    I've never neasured it - I don't think it ever occurred to me to check. All the tools I'm using at high RPM are 3/8" and under so they've never taxed the motor very much.

  6. #26
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    Re: New spindle motor - Servo or Induction?

    i take that back, you can get 1hp at 3600 rpm from your existing motor no problem, but that's about the limit before the motor efficiency drops causing increased heating.

    switching to a 2 hp 3600 rpm motor, you would want to reverse the belt ratio, as the motor will only deliver half the torque a 1800 rpm motor can.

  7. #27
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    Re: New spindle motor - Servo or Induction?

    That's why I'm leaning towards an AC servo. Keeping in mind my very limited motor knowledge, the torque curves for 1.5-2.2Kw servos rated in the 6k-8k range appear pretty favorable and should let me cut the belt ratio down for better low-end torque without running out of spindle RPM.

    Even if I wind up with a standard (not "spindle") servo I think an external cooling fan shouldn't be too hard to retrofit.

  8. #28
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    Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by spumco View Post
    That's why I'm leaning towards an AC servo. Keeping in mind my very limited motor knowledge, the torque curves for 1.5-2.2Kw servos rated in the 6k-8k range appear pretty favorable and should let me cut the belt ratio down for better low-end torque without running out of spindle RPM.
    can you link me to one of these motors?

  9. #29
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    Re: New spindle motor - Servo or Induction?

    Here's what I'm looking at, more or less. There are a number of manufacturers that make similar servos in the same RPM, amp, torque, etc. range.

    Mostly they're the 'big name' companies, not typical AliExpress variety. Parker, ABB/Baldor, Kollmorgan, etc.

    https://divapps.parker.com/divapps/e...orBrochure.pdf

  10. #30
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    Re: New spindle motor - Servo or Induction?

    i didn't look into it too much but it appears for the same KW or HP, you can get a servo that is a third the weight of a 3600 rpm induction motor. and this is no surprise because the base speed is about double that, at 5-7000, and the neodymium magnets offer nearly double the flux density which means 4 times the magnetic force. its interesting to me that the peak torque (60 seconds, plenty for rigid tapping) is 3-4 times the base torque. this is much better than an induction motor which the peak torque is only ~2 times the rated constant torque.


    so yeah, servos are better. or just buy a 30-40 pound 2hp 3600 rpm induction motor and flip your belt around from 1.5:1 to 1:1.5. it will save you ~30 pounds on the spindle. you'll still have the same fundamental motor hp-torque curve as you do now.

    my suggestion to wire the motor for 140vac will reduce your low end torque to merely 1.2 times nameplate* (rather than double the nameplate torque), but it will increase your high end torque significantly, all the way out to 5000 rpm, netting you 3 hp from a 2 hp motor at about 5000 rpm.. however, from the sound of it, you may not need 2hp at high speeds.


    as it is now you're running a 1800 rpm 230 vac motor up to 5000 rpm at the motor to get 7500 rpm at the spindle?

    *assuming you keep the same vfd limited to 11 amps, when the motor needs 9 at full load, where as before when wired for 230vac it only needed 5.5

  11. #31
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    Re: New spindle motor - Servo or Induction?

    as it is now you're running a 1800 rpm 230 vac motor up to 5000 rpm at the motor to get 7500 rpm at the spindle?
    Correct. I haven't bogged down the motor with large tools at high RPM yet, but I'm not really after max roughing MRR at high spindle speeds. My mill isn't really rigid enough to be super-aggressive. I just run some small tools fairly frequently so I don't want to give up any RPM. In fact, I'd really like to get a 10k spindle, but that's down the road a bit.

  12. #32
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    Re: New spindle motor - Servo or Induction?

    So in order to save 30 pounds you have to run a 2 hp 3600 rpm motor at 10,000 rpm in order to get 7500 at the spindle, while also preserving the same low end torque you have now.

    what's the largest tap you use on the machine?

  13. #33
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    Re: New spindle motor - Servo or Induction?

    1/2-13 in mild steel would be about the biggest tap I would drive at low RPM. Anything bigger and I'll get a threadmill.

    The other low-RPM, high load tool would be a 2" face mill, also in steel.

  14. #34
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    Re: New spindle motor - Servo or Induction?

    a 1/2-13 tap could be on the order of 143 inch pounds, low carbon steel 170BHN which is also 16N.m.
    https://www.kennametal.com/en/resour...orsepower.html

    given your belt ratio of 1.5:1 that's 6 hp at the motor at 1800 rpm.
    WEN Technology - Calculators

    which means: given that you probably use a larger drill bit than one for 75% thread.. you may be close to maxing out the 11 amps you have available from the vfd to drive your spindle motor close to the limit of 2 - 3 times full load torque available from most induction motors.

    so from that pdf you linked to, you may need the largest one in it, the N0924K

    once you allow for changing the belt ratio, you can use a much smaller motor to get the same job done.

  15. #35
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    Re: New spindle motor - Servo or Induction?

    Here is a real world experience from yesterday. Drill & tap through, 1/2-13, 7/16 drill (~ 60% thread depth), 1 inch thick A36 steel (mild steel, hot rolled). 3 HP Baldor motor, 4 pole. GS3 sensorless vector VFD. Geared up 1.5:1. New OSG spiral point tap, proper chamfer for lead in on the hole, good tapping fluid. 220 spindle RPM. Spindle load while tapping = 150%, I could feel the VFD current limiting.

    Bottom line, that's all the system had. If the tap would have been dull it would have stalled the motor. Maybe this is useful to you.
    Jim Dawson
    Sandy, Oregon, USA

  16. #36
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    Re: New spindle motor - Servo or Induction?

    Jim - extremely useful. Explains why I've had to peck tap 3/8-16 a few times (dull tap?) and my spindle does struggle with 1/2-13 even with high-sulfur oil..

    HSMAdvisor is telling me it's a 2HP operation with the 7/16" hole, and I usually tap at 4-500RPM.


    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

  17. #37
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    Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by spumco View Post
    HSMAdvisor is telling me it's a 2HP operation with the 7/16" hole, and I usually tap at 4-500RPM.
    hp is a function of rpm and torque.

    did it tell you 2hp at 500 rpm? because that would be similar to the 6hp at 1800 rpm i mentioned.

  18. #38
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    Re: New spindle motor - Servo or Induction?

    I pulled the trigger and ordered this big baby. https://www.campeongroup.es/es/motor...tor-43-ct-info

    96mm diameter but it's long however I expect it about 200mm when I complete the new case. I'll buy a Siemens Sinamics V20 3kw inverter for it.

  19. #39
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    Re: New spindle motor - Servo or Induction?

    Quote Originally Posted by Eldon_Joh View Post
    hp is a function of rpm and torque.

    did it tell you 2hp at 500 rpm? because that would be similar to the 6hp at 1800 rpm i mentioned.

    Yes, 2.02hp at 628RPM to be exact.

  20. #40
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    621

    Re: New spindle motor - Servo or Induction?

    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,
    Gecko G540, Rack and Pinion Drives-X and A axis, 1/2-10 5 Start Acme-Z Axis
    4-THK HSR 25 Linear Slides, KL23H2100-35-4B, Power Supply-KL-600-48 48V

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