Servo motors vs the other motors

[john lucas]

I'm really unfamiliar with servo motors. What are the advantages and disadvantages. To they require a special power supply. Can you retrofit one to other lathes, specifically mini or midi lathes.

 

[Rusty Nesmith]

I have only worked with large servo motors. They require a controller like a VFD. You set an rpm and it will stay there no matter how light or heavy the load until you reach over current. They are very quiet. They cost quite a bit more to replace than a regular motor.

 

[Don Wattenhofer]

I read thru the specs for the lathe in question;
The propaganda portion said the motor can be loaded up to 3 HP.
The specs say 1Hp Imperial or 750 watts Metric.
The NEMA (US) standard rates motors in continuous mechanical output so due to inefficiency about 1000 watts input power would be required per HP.
The EEC code is unclear to me if the watt rating is mechanical output or electrical power input and if it is the input then the mechanical power is less than 1 HP or 750 watts.
The standard 3 ph induction motors as used on most lathes have just as much if not more overload torque plus the VFD controllers have long ago reached commodity status.
The Servo controller and the servo motor will likely only be available from Harvey at inflated prices and are probably low quality.

 

[Dean Center]

I read thru the specs for the lathe in question;
The propaganda portion said the motor can be loaded up to 3 HP.
The Servo controller and the servo motor will likely only be available from Harvey at inflated prices and are probably low quality.

I believe John posed a general question about servo motors and was not soliciting criticism of a particular product or of anyone's lathe choice.

 

[john lucas]

I'm interested in all.discussions concerning these motors. I have not had time to actually look them up a d try to understand tech speak.

 

[Don Wattenhofer]

I believe John posed a general question about servo motors and was not soliciting criticism of a particular product or of anyone's lathe choice.

I was only criticizing the deceptive marketing and trying to find a reason for a servo motor verses an ordinary induction motor.

 

[Brian Gustin]

Basics of a servo motor, as I understand it, the motor can vary speed by means of changing supplied voltage.. a servo motor would have a speed sensing device so that when you set it to a specific speed it can detect when it starts to slow down (loading) or speed up (unloading) and within milliseconds, vary the voltage going to the motor in order to maintain a constant speed .. So, it seems to me, if the motor has enough power/torque in reserve, it should be able to maintain a very consistent and constant speed regardless of the amount of loading being applied to the work... Much like the Anti-Lock brakes system on a car, (and/or traction control system) which can spot changes in wheel speeds relative to other wheels and apply braking logic to select corner of the car to maintain traction or prevent lockup... by means of speed sensors... Seems to me, a servo motor would typically be able to maintain a smooth steady speed in varying conditions, as opposed to a belt drive which can slip or be limited to its torque to within a specific speed range (Torque curve)... But then, I am no engineer.. it is just my understanding of how a servo motor (as far as maintaining speed) would work.. The servo motors I am more familiar with are more like robotic controls (electronic governors, electronic throttles, electronic climate controls, and the like.. which are more of a linear control as opposed to rotational control)

 

[Karl Loeblein]

Don, I think you make a good point that we shouldn’t use the HP rating in sales brochure when comparing the output of one motor type (servo) to another motor type (3ph VFD motor). Sure there are other things to discuss regarding servo motors, but it’s nice to be reminded when HP ratings could mislead some people into making an unfair comparison between motor outputs.

Setting aside hp rating, do you think this servo is a reasonable size for this type of lathe based on the wattage?

 

[odie]

Basics of a servo motor, as I understand it, the motor can vary speed by means of changing supplied voltage.. a servo motor would have a speed sensing device so that when you set it to a specific speed it can detect when it starts to slow down (loading) or speed up (unloading) and within milliseconds, vary the voltage going to the motor in order to maintain a constant speed .. So, it seems to me, if the motor has enough power/torque in reserve, it should be able to maintain a very consistent and constant speed regardless of the amount of loading being applied to the work... Much like the Anti-Lock brakes system on a car, (and/or traction control system) which can spot changes in wheel speeds relative to other wheels and apply braking logic to select corner of the car to maintain traction or prevent lockup... by means of speed sensors... Seems to me, a servo motor would typically be able to maintain a smooth steady speed in varying conditions, as opposed to a belt drive which can slip or be limited to its torque to within a specific speed range (Torque curve)... But then, I am no engineer.. it is just my understanding of how a servo motor (as far as maintaining speed) would work.. The servo motors I am more familiar with are more like robotic controls (electronic governors, electronic throttles, electronic climate controls, and the like.. which are more of a linear control as opposed to rotational control)

Assuming that Brian is correct, and maintaining a constant speed is the difference between it and a DC motor with VFD, it leads one to contemplation as applied to woodturning. I'm theorizing how that can be applied to what we know concerning how vibrations emanating from the wood relates to the load applied to it, as it varies for light vs heavy cuts, and the overall quality of the cut.

My initial thought on this, is a servo motor has no benefit applicable to woodturning. As the amount of wood being removed increases with a heavy cut, it has a direct relationship to the amount of vibration emanating from the source. This, instead of maintaining a constant rpm, is what directly effects the quality of the cut that is possible.

I spend a lot of effort finding a most perfect rpm, but that is only helpful for the finest of finishing cuts, where the changing dynamics of the cut is at it's least point. Once a heavy cut comes into play, the whole dynamics relating to the quality of the cut changes. Since those dynamics change, maintaining a specific rpm is no longer a determining factor in those things that promote the best cut.

My thoughts are not the result of actual experience with a servo motor, so I'm interested to hear further discussion from those who do have the experience.....or, from those who have additional theoretical thoughts.

-----odie-----

 

[Don Wattenhofer]

Assuming that Brian is correct, and maintaining a constant speed is the difference between it and a DC motor with VFD, it leads one to contemplation as applied to woodturning. I'm theorizing how that can be applied to what we know concerning how vibrations emanating from the wood relates to the load applied to it, as it varies for light vs heavy cuts, and the overall quality of the cut.

A DC motor is not controlled by a Variable Frequency Drive, there is only 1 type of motor that operates on a VFD and that is an AC 3 phase induction motor. The VFD / 3ph motor combination will maintain a constant speed sufficient for wood turning. Servo motors are normally used to supply adjustable constant speed and positioning control on machine tool axis.

 

[john lucas]

Part of why I asked this question was because I've gone through several.lathes and changed motors and drives. My first 2 lathes were single speed motors with Reeves drives. They werent bad but you had to keep the parts clean and could only vary the speed.with the lathe running which was interesting if you turned a pen at 3000 rpm and then your next project was a bowl and you forgot to crank the speed.down. my next lathe was single speed with a step.pulley. I converted it to a DC drive. The DC drive had a problem of losing power when you lowered the speed which of course was a.problem when roughing bowls. I learned about 3 phase motors and variable frequency drive so I installed one of those. They maintain the power at low rpms which was great. You also get reverse and electronic breaking. So im.wondering what the advantage are.of servo motors over 3 phase motors a d VFD s.

 

[odie]

A DC motor is not controlled by a Variable Frequency Drive, there is only 1 type of motor that operates on a VFD and that is an AC 3 phase induction motor. The VFD / 3ph motor combination will maintain a constant speed sufficient for wood turning. Servo motors are normally used to supply adjustable constant speed and positioning control on machine tool axis.

Hello Don......This is the motor I have on my Woodfast lathe:

https://www.woodturnerscatalog.com/p/110/5521/leeson-DC-Variable-Speed-Control?term=leeson+minarik&term=leeson minarik

Leeson DC Variable Speed Control 1-1/2 HP 220v

-----odie-----

 

[Glenn Lefley]

I think the answers lies in why all the big well known wood lathe companies, where cost is not a factor and have used the best parts they can, have never used a servo motor. But one company is now boosting a servo motor on their seemingly over priced and questionable marketing literature on their servo motor. I for one will never be the guy that buys the new car the first year off the line. I always let the other guy buy all the bugs and problems in a new build. If it’s around by the second and third year one can read about all the pros and cons of the new product in real life. Then make an informed decision. A company will never tell you the limitations of the new lathe, just give you all the marketing hype they print in there selling literature. Maybe in 10 years all lathes will have servo motors, or this one will be long gone. We shall see in time.

 

[Larry Mitchell]

Hail to the pioneers and those that blaze the new path. Lighten up guys!!

 

[Rusty Nesmith]

Servo motors have been used on metal lathes for years. Nothing wrong with servo motors. They will hold a constant rpm. They are very quiet. I don’t have experience with small ones. I have installed 15 HP to 40 HP on plastic extruders, form presses, trim presses, grinders and other machines. They ran 24/7/365 for years with no problems. Larry I wouldn’t worry about. It’s not like it’s new technology.

 

[Larry Mitchell]

Thanks for your input Rusty...not worried. Not new, just different application.

 

[Rusty Nesmith]

Thanks for your input Rusty...not worried. Not new, just different application.

I wouldn’t be surprised to see other companies start using servo motors in the future.

 

[Larry Mitchell]

I wouldn’t be surprised to see other companies start using servo motors in the future.

OMG Rusty....you’re speaking blasphemy!! LOL

 

[john lucas]

Thanks Rusty.

 

[Glenn Lefley]

Hello Don......This is the motor I have on my Woodfast lathe:

https://www.woodturnerscatalog.com/p/110/5521/leeson-DC-Variable-Speed-Control?term=leeson+minarik&term=leeson minarik

Leeson DC Variable Speed Control 1-1/2 HP 220v

-----odie-----

Odie your dc motor is controlled by a vsd. The variable speed drive changes the voltage to control the speed. Hence they can be used on dc and ac motors. A vfd changes the frequency of the wave and the voltage and hence can only be used on a ac motor, Don is right. Unless I’m reading your reply wrong Odie.

 

[Jon Minerich]

Guys,

I have been using my Harvey with a 1hp servo motor for over a year. After running it several times a week during this time, I have not had a single problem. It runs smoothly and quietly. Because I am not a production turner who has to maximize wood removal, I have never bogged it down.

One thing nobody has mentioned is size and weight of those ac motors compared to my servo motor. It is small in comparison. I bought the lathe to fit into my tiny shop. I needed a compact, powerful lathe for my style of turning. The Harvey T-40 fit the bill.

By the way, it was cheaper than the PM 2014.

Jon

 

[odie]

Odie your dc motor is controlled by a vsd. The variable speed drive changes the voltage to control the speed. Hence they can be used on dc and ac motors. A vfd changes the frequency of the wave and the voltage and hence can only be used on a ac motor, Don is right. Unless I’m reading your reply wrong Odie.

OK, got it, Glenn! I wasn't aware of the difference.

In my original sentence using VFD incorrectly, the substance remains the same. I'm not seeing any benefit to a constant speed, for the reasons I mentioned. Now, if there is a real benefit to the act of woodturning, and not about the size of the motor (as in @Jon Minerich post above this one), I'd like to know more about it.

Assuming that Brian is correct, and maintaining a constant speed is the difference between it and a DC motor with VFD, it leads one to contemplation as applied to woodturning. My initial thought on this, is a servo motor has no benefit applicable to woodturning.

 

[Glenn Lefley]

OK, got it, Glenn! I wasn't aware of the difference.

In my original sentence using VFD incorrectly, the substance remains the same. I'm not seeing any benefit to a constant speed, for the reasons I mentioned. Now, if there is a real benefit to the act of woodturning, and not about the size of the motor (as in @Jon Minerich post above this one), I'd like to know more about it.

I’m not seeing any benefit either. I assume my Oneway has enough torque to keep a constant speed. And I doubt the Harvey lathe cannot be stalled like any other lathe. Now if it had a 20 hp servo motor that would make a difference, but it would also mske a similar difference if my oneway had a 20 hp motor.

 

[Doug Rasmussen]

One thing for sure is if the servo motor or its drive needs replacement it's going to be more expensive than an equivalent AC motor or VFD.

Example: on one of my machine tools a Baldor servo motor was not performing as it should. Baldor referred me to a factory authorized repair outfit to have the motor repaired. After a $200 diagnosis they decided it couldn't be repaired. $1100 later I ended up with a new Baldor servo motor. That was a lot of money for a motor of that size. $1100 will go quite a ways toward an AC motor and a VFD.

If maintaining constant speed (rpm) under load is the issue you can achieve that with a flux vector AC motor and VFD (more expensive than conventional AC motor and VFD). The motor rpm is monitored by the drive and corrects as needed.

 

[stu senator]

Servo motor is a broad category. What is the type of servo, DC, AC Stepper motor we are talking about? They are all different and require different type of driver and have different responses.

As for the power (HP) of the motor. Some types have large thermal mass and can take quite a bit of over-current for a brief period of time. The power must come thru the power supply (driver) and can be momentary. I assume this is what the advertisement is about. Is this good engineering, or marketing. As an engineer I did not like to tell marketing everything and this is why

 

[Rusty Nesmith]

One thing for sure is if the servo motor or its drive needs replacement it's going to be more expensive than an equivalent AC motor or VFD.

Example: on one of my machine tools a Baldor servo motor was not performing as it should. Baldor referred me to a factory authorized repair outfit to have the motor repaired. After a $200 diagnosis they decided it couldn't be repaired. $1100 later I ended up with a new Baldor servo motor. That was a lot of money for a motor of that size. $1100 will go quite a ways toward an AC motor and a VFD.

If maintaining constant speed (rpm) under load is the issue you can achieve that with a flux vector AC motor and VFD (more expensive than conventional AC motor and VFD). The motor rpm is monitored by the drive and corrects as needed.

We used to have our 15 HP servo motors rebuilt for $5,000 because a new one was around $11,000.

 

[Michael Colley]

Does anyone know how long Harvey has been manufacturing the T40&T60?
And is anyone here using the T60 for a good amount of time that could offer input?
Thanks

 

[robo hippy]

No clue to what or how the servo motors do, or if they have any advantages. Time will tell. One comment from Brent at Robust, was that the new 3 phase motors are so efficient that the new lathes really don't need speed ranges. I would have to test it out first to see if that is true. As for DC motors, they have come a long way in the last 20+ years. I think the first ones I saw were on one of the old Nova lathes. They were very finnicky in their performance ranges, and you needed to be able to tinker with them for optimal performance. I picked up a Rikon mini lathe and I was told that with the DC motor on it, I would not lose torque at slow speeds like with the AC motors. Not sure how that worked, but I am not a fan of the pause before the motor engages. When I turn the knob, I want the motor to instantly start up. That pause drives me nuts!

One question from me, the Nova DVR motors, are they any relation to the servo motors? I am still surprised at how much torque they have for such a small motor, size wise anyway....

robo hippy

 

[Brent@TurnRobust]

From Reed: "One comment from Brent at Robust, was that the new 3 phase motors are so efficient that the new lathes really don't need speed ranges."

Reed, I never said that. If you want to have a private conversation with me, please send an email.

 

[Brian Gustin]

Does anyone know how long Harvey has been manufacturing the T40&T60?
And is anyone here using the T60 for a good amount of time that could offer input?
Thanks

I know a couple members here at least that have a T60. Harvey has been building machinery for other companies for years (I believe they built the powermatics, for one, if I recall right....) but they have been making their own branded machinery for quite a while, and I have not heard much in the way of negatives from users (insofar as my YouTube viewing habits permit), and I know their Hand tools (Bridge City Tool Works) are superb top of the line quality (Not just pretty , but highly usable and innovative to boot).. I would have one (Harvey) myself, if I had the moolah (and I keep debating whether to go for a T40 when I have the money , and get a bed extension ... or save up and get the Jet 1840 I can barely afford... I keep going back and forth, but still havent come up with the budget to pull the trigger either way yet) I do believe they are quite top notch in customer service however.

 

[Doug Freeman]

One question from me, the Nova DVR motors, are they any relation to the servo motors? I am still surprised at how much torque they have for such a small motor, size wise anyway....

No. DVR motor is an AC switched reluctance motor (can find explanations online). The dvr setup does monitor shaft speed and maintain speed. To @odie ’s point, not relevant for finish cuts but it sure helps when hogging off waste material. The torque difference between 1-1/2 hp rated dvr vs vfd system is substantial.

 

[Vitor Cruz]

Dear all,
Servomotor is a closed-loop servomechanism that uses position feedback to control its motion and final position.

Servomotor - Wikipedia

en.wikipedia.org

 

[Gerald Rutledge]

The Harvey T-40 is on sale for America's Birthday at $1800 USD right now. It has been on sale off and on for the last couple of years. When it is on sale, it is reasonably competitive with other machines in the same league. The $2800 MSRP is more of their marketing shenanigans, one can regularly find it offered for 25% to 35% off, just as it is now.

The servo motor seems pretty stout to my own inexperienced self on my T-40. It is about the size of a soda can. The machine is super-quiet, but at some very specific speeds it has a faint, high-pitched electronic ring. It is very responsive and the torque holds up just as well at 0 rpm as anywhere else, but I have not tested that scientifically.

It does use drive belts for a high and a low ranhe, so it can experience a "soft stall" depending on belt tension. I try not to over-tension it to reduce stress on the belt and undue strain on the bearings, but I honestly have no idea what the appropriate tension level actually is. My suspicion is that if I get to a point where it does stall, soft or otherwise, then I could just back the cut off a little. The torque to swing ratio it has doesn't seem likely to cause much stalling, though.

There is a lot of emphasis put on the price, but I think the T40 is competitively priced with its peers (quality, features, size, and yes, customer service), if you are willing to wait for a sale. The discount cycle for the T-40 seems to be about 6 to 8 weeks. Again, it's a great price on it right now for Uncle Sam's birthday, the lowest I have seen in 18 months.

In fairness and impartiality, a PM 2014 is a little bit cheaper right at this moment at $1500, but IMO, the ridiculously short bed is a non-starter for me. I looked at other peers before I posted, some of which never seem to go on sale for any substantial amount (looking at you, Jet), and there are a lot of variables to consider. Some features are must-have or deal-killers, etc. Some machines that look like peers really aren't.

Getting back to the topic:
The motor on mine is a Delta model ECMA-C10807RH.
Made in Taiwan.
Edit: dug a bit more, one website is selling the motor for $500. Ouch, indeed.

 

[Doug Freeman]

I'm really unfamiliar with servo motors. What are the advantages and disadvantages. To they require a special power supply. Can you retrofit one to other lathes, specifically mini or midi lathes.

Yes a servo motor could be retrofitted, but the mounts would be custom one-offs. Would be interesting to see a price comparison of servo and vfd drive systems for such a project. I suspect the servo system could be substantially more $’s.

 

[Don Wattenhofer]

No. DVR motor is an AC switched reluctance motor (can find explanations online). The dvr setup does monitor shaft speed and maintain speed. To @odie ’s point, not relevant for finish cuts but it sure helps when hogging off waste material. The torque difference between 1-1/2 hp rated dvr vs vfd system is substantial.

Since HP is a combination of torque and rated speed what is the rated speed of the DVR motor rated at 1 -1/2 HP?
The torque of a VFD controlled induction motor is constant through it's frequency range but if the VFD is set to put out a higher frequency then the torque drops off when it can no longer can maintain the volts per Hertz ratio.

 

[robo hippy]

Brent, maybe I got that wrong, but that was my memory. Can't remember. Apologies! My Liberty lathe from you only has one speed. I think I still prefer 3 speed ranges. Lowest for sanding, medium for all bowl turning and coring, and high for spindles.

robo hippy

 

[Doug Freeman]

Since HP is a combination of torque and rated speed what is the rated speed of the DVR motor rated at 1 -1/2 HP?

Don’t know, Nova doesn’t say, and doesn’t publish an rpm/hp-t chart, though I wish they would.