Chapter 2: Frequency Inverter

[Emiliano Achaval]

(continued from Chapter 1: Omega Lathes Stubby 750 VFD)

I replaced my old VFD on my Stubby 750 with a WEG CFW 500 V1 8X
I'm not happy with it. I had a club member engineer over, he tweaked it but still not working right. I do not have torque. What looks like the main torque parameter P0009 suppose to be adjustable to 1000%, but you can't adjust it. It's at ZERO. If anybody uses this unit, can you send me your parameters? I have another guy coming tomorrow to take a look. Also, Rod Caddeye from Omega lathes is going to a customers shop tomorrow with a Stubby and a WEG unit; he will send me the parameters too. I'm just trying to see what others are using. The WEG is an upgraded unit over what the Stubby comes from the factory. I wish I didn't upgrade; the other unit is proven, this one supposes to be way better, my engineer friend told me is worth the extra money. He recommends one unit that cost as much as a lathe, a top of the line lathe. Thanks in advance.

 

[Mike Johnson]

Most drive manufacturers have a phone number you can usually call and a technician that can walk you through a parameter issue. You could also try sending an email message to their website to see if a technician or engineer can assist you.

 

[Emiliano Achaval]

After 6 hours of troubleshooting, we think that I also need a new motor. Found a WEG dealer on the Island... Stay tuned.

 

[John Jordan]

I would be skeptical. Three phase motors used for lathe duty basically never go bad. I would take the motor to someone with a powermatic, robust or anything with a variable frequency drive and hook it to that. It would be a strange coincidence for both to go bad at the same time.

John

 

[Bill Boehme]

I would be skeptical. Three phase motors used for lathe duty basically never go bad. I would take the motor to someone with a powermatic, robust or anything with a variable frequency drive and hook it to that. It would be a strange coincidence for both to go bad at the same time.

Ordinarily that would be true, but when used with an inverter general purpose motors are susceptible to a number of problems if they aren't rated as either "inverter ready" or even better designed specifically for "inverter duty". The attached PDF file might be somewhat technical, but I think that the basic message still comes through: https://www.energy.gov/sites/prod/files/2014/04/f15/motor_tip_sheet14.pdf

 

[Emiliano Achaval]

Ordinarily that would be true, but when used with an inverter general purpose motors are susceptible to a number of problems if they aren't rated as either "inverter ready" or even better designed specifically for "inverter duty". The attached PDF file might be somewhat technical, but I think that the basic message still comes through: https://www.energy.gov/sites/prod/files/2014/04/f15/motor_tip_sheet14.pdf

The Stubby came with a motor that was probably a very cheap option. We learned that over time they can lose torque. That's what's happening, I don't have torque. The old Eaton controller was probably fine! I have the same problem with an $1800 WEG VFD. I'm trying to find out a model number for a WEG motor, called them today and they have no idea what I need. I got some specs from Rod, but no model number. My engineer friend is looking for me...

 

[Emiliano Achaval]

Ordinarily that would be true, but when used with an inverter general purpose motors are susceptible to a number of problems if they aren't rated as either "inverter ready" or even better designed specifically for "inverter duty". The attached PDF file might be somewhat technical, but I think that the basic message still comes through: https://www.energy.gov/sites/prod/files/2014/04/f15/motor_tip_sheet14.pdf

So, I might not be crazy after all! Motors do fail over time. Most people tell me they either work or they don't, that when they fail they fail catastrophically. Not the case with mine, I hope!

 

[Bill Boehme]

So, I might not be crazy after all! Motors do fail over time. Most people tell me they either work or they don't, that when they fail they fail catastrophically. Not the case with mine, I hope!

I've been preaching that for years, but I think that nobody has paid attention to what I have been saying.. The insulaton breakdown problem is insidious and performance gradually declines over several years so it goes unnoticed until performance starts rapidly declining near the end.

 

[Emiliano Achaval]

I've been preaching that for years, but I think that nobody has paid attention to what I have been saying.. The insulaton breakdown problem is insidious and performance gradually declines over several years so it goes unnoticed until performance starts rapidly declining near the end.

I'm so glad to hear this Bill. It has been so frustrating. Yesterday my engineer friend started asking questions, to understand better what's going on. Most I was like: NO, NO, NO. And then he asked "THE" question: What was the problem before, why did I buy a new VFD unit, what was the lathe doing with the old VFD and the same motor? I felt a little embarrassed! The answer is, the motor started gradually losing torque before. Everybody blamed the old Eaton VFD. I bought the new WEG VFD and I expected instant super torque and I didn't have it, of course, we blamed the parameters, we changed and tweaked everything, nothing helped!! Rod Caddeye sent me the "new parameters" still no torque. I'm almost willing to bet my house that the problem IS the motor!! We are now trying to figure out what motor from WEG I need. I called them and have no idea, even though I gave them lots of specs. My friend is trying to use an online configurator so he can give me a model number. I also posted the question to our Stubby groups online on the new platform, Groups.io You made my night! Thanks again! Aloha

 

[Richard Coers]

I'm curious to know why you haven't taken the motor to a shop and have it evaluated? Pretty expensive buying new hardware with the hopes of fixing the lathe.

 

[Doug Rasmussen]

The Stubby came with a motor that was probably a very cheap option. We learned that over time they can lose torque. That's what's happening, I don't have torque. The old Eaton controller was probably fine! I have the same problem with an $1800 WEG VFD. I'm trying to find out a model number for a WEG motor, called them today and they have no idea what I need. I got some specs from Rod, but no model number. My engineer friend is looking for me...

Are you saying you paid $1800 for a VFD for a wood lathe? If so, somebody is leading you astray.

As to a new motor I believe all new industrial grade Baldor motors are inverter duty. You shouldn't need a WEG motor (which might have a price to match their inverter pricing).

 

[John Jordan]

I sold hundreds of Stubbys and a bunch of Oneways, and have used thousands, and I just have not seen it. I replaced one Stubby motor for a balance issue.

I know of a few VFD's that have had to be replaced on various brands of lathes, including several older Stubbys. They eventually become heavily dust covered internally.

 

[Emiliano Achaval]

I'm curious to know why you haven't taken the motor to a shop and have it evaluated? Pretty expensive buying new hardware with the hopes of fixing the lathe.

The joys of living on the mainland. Called 2 places to have the motor repair. They send the motor out to Oahu. Shipping is about the same than buying a new motor. I'd rather buy a new one.

 

[Emiliano Achaval]

Are you saying you paid $1800 for a VFD for a wood lathe? If so, somebody is leading you astray.

As to a new motor I believe all new industrial grade Baldor motors are inverter duty. You shouldn't need a WEG motor (which might have a price to match their inverter pricing).

I purchased the upgraded weg unit from the factory in Australia, from owner Rod Caddeye. He’s hardly leading me astray. Not a very nice comment from your part. I'm also buying a new Stubby 1000 from him. One or two large Koa or Milo bowls cost more than what I paid for the unit. Shipping for a Baldor unit would be more than the cost of the motor, or I could wait up to 2 months.

 

[Bill Boehme]

As to a new motor I believe all new industrial grade Baldor motors are inverter duty. You shouldn't need a WEG motor (which might have a price to match their inverter pricing).

No that isn't correct although most of their three phase industrial motors are probably "inverter ready". There is a huge difference between that and "inverter duty". By the way, on a somewhat sad note, Baldor isn't Baldor any more. They were bought out by a Swiss conglomerate a few years ago and effective some time last year everything that was Baldor is being rebranded as "ABB". Here's the "happy news" press release.

 

[Emiliano Achaval]

No that isn't correct although most of their three phase industrial motors are probably "inverter ready". There is a huge difference between that and "inverter duty". By the way, on a somewhat sad note, Baldor isn't Baldor any more. They were bought out by a Swiss conglomerate a few years ago and effective some time last year everything that was Baldor is being rebranded as "ABB". Here's the "happy news" press release.

Well, I have posted here and at our Stubby users group. I’m going with Bill’s wisdom. Called Weg today, and within minutes I had a model number and a specs sheet. Albert Einstein double checked and I placed an order for it. Thank you everyone for all the great suggestions. Bottom line is I do not have time to keep testing, checking, taking the motor to shops for more testing and repairs. I turn every day and I can't afford the downtime. The new motor is $489. landed on this rock. I have a Milo bowl on it right now that is worth more than the motor. For future reference this is the motor parts number and the WEG parts number. If you google the long number and weg you can see it. I also have a pdf with all the specs if anyone needs it. I will report back when I replace the motor. Aloha.
00158ET3WAL90LFF-W22 | Product: 13984012

 

[Richard Coers]

Almost $2,300 for the new VFD and motor? Ouch!!!!!!

 

[Bill Boehme]

Almost $2,300 for the new VFD and motor? Ouch!!!!!!

Not to worry, he will make the expense back in one or two calabash bowls.

 

[Gerald Lawrence]

Not to worry, he will make the expense back in one or two calabash bowls.

Bill technically on a retail basis he will not make it back . It is business expense and will reduce net so he can break even but still be behind.

 

[Emiliano Achaval]

The saga continues. Today, Omega Lathes owner Rod Caddeye call me to tell me he's as frustrated as I am. He contacted his WEG vendor and told them the situation. I had to send him pictures of my motor specs, the plate on it, and the sticker on the side of the VFD unit. They are blaming the parameters. I had "Einstein" working on it for 6 hours, I doubt the parameters are the cause. My new Stubby 1000 is almost ready to ship to me if we can't find a solution he's adding a new VFD and a 3hp motor to the pallet!! Let's see what the WEG people come up with ... Meanwhile, the new motor I ordered, because it is a special order, I can't cancel it...

 

[Bill Boehme]

I assume that that WEG wants the suspect motor and VFD in order to conduct a formal failure investigation ... or, at least I think that they should. Once upon a time, increasing your knowledge base was the smart thing to do ... these days it seems like pinching pennies is the smart thing to do.

 

[Mike Johnson]

Electricity is based on a theory, every once in a while it defies all logic.
Without the expense of sending the motor or VFD back to the factory for analysis, the easiest way to troubleshoot the issue is to try a different motor with your VFD and a different VFD with your motor. With several basic electrical meters you can usually determine if a motor is good or bad. The VFD gets a bit more complex in diagnosing problems, in most cases the installer when swapping out a VFD will get the line and load connections reversed and will attempt to start the motor and this usually compromises the VFD and "lets the smoke out". The average VFD manual is about a 1000 pages or more in length which can be confusing for the average person to read and locate all of the appropriate parameters needed to set the drive up properly. The facility I work at we have 1000's of motors on site and the ones we power off of VFD's we archive and save the settings when the equipment is commissioned to speed the process if and when the equipment fails. Having the VFD settings saved to a thumb drive is a good insurance policy for dealing with these kind of problems which always occur sooner or later. Anything that runs off of electricity will fail some day, it is only a matter of when.

 

[Emiliano Achaval]

Electricity is based on a theory, every once in a while it defies all logic.
Without the expense of sending the motor or VFD back to the factory for analysis, the easiest way to troubleshoot the issue is to try a different motor with your VFD and a different VFD with your motor. With several basic electrical meters you can usually determine if a motor is good or bad. The VFD gets a bit more complex in diagnosing problems, in most cases the installer when swapping out a VFD will get the line and load connections reversed and will attempt to start the motor and this usually compromises the VFD and "lets the smoke out". The average VFD manual is about a 1000 pages or more in length which can be confusing for the average person to read and locate all of the appropriate parameters needed to set the drive up properly. The facility I work at we have 1000's of motors on site and the ones we power off of VFD's we archive and save the settings when the equipment is commissioned to speed the process if and when the equipment fails. Having the VFD settings saved to a thumb drive is a good insurance policy for dealing with these kind of problems which always occur sooner or later. Anything that runs off of electricity will fail some day, it is only a matter of when.

Are you coming to Maui anytime soon? It looks like I could use your help! Bring an empty suitcase. Payment will be in Koa blanks.

 

[Karl Loeblein]

I purchased the upgraded weg unit from the factory in Australia, from owner Rod Caddeye. He’s hardly leading me astray. Not a very nice comment from your part. I'm also buying a new Stubby 1000 from him. One or two large Koa or Milo bowls cost more than what I paid for the unit. Shipping for a Baldor unit would be more than the cost of the motor, or I could wait up to 2 months.

Emiliano, Just curious about the specs on your WEG VFD? Like Doug, I'm also wondering why your WEG unit would cost so much for running a 2HP motor.

For example: This WEG CFW500 AC Drive from Factory Automation large enough to run a 3HP motor only cost $324 (without any programming).

WEG CFW500 AC Drive, 3HP, 230V 1 PH/3 PH Input, 230V 3 PH Output, 10FLA, includes Braking Transistor, IP20
https://www.factorymation.com/CFW500B10P0B2DB20
​

I'm not doubting you're ability to cover the cost, but wondering if the VFD programming makes it that much more expensive? Just wondering in case someday my old VFD (or motor) goes out on my Vicmarc VL300 Lathe.

 

[olaf Vogel]

Hey Emiliano, I'm a bit late to the conversation, so forgive me for a few assumptions.

You don't state anywhere what your core need is for the high torque. So I assume its for large bowls (coring) on hard wood, likely at low speeds.
While I've not seen a Stubby 750 in person, from the pics, it looks like there is no mechanical gearing. Hence speed control is entirely via VFD.

Is that correct?

 

[Bill Boehme]

Emiliano, Just curious about the specs on your WEG VFD? Like Doug, I'm also wondering why your WEG unit would cost so much for running a 2HP motor.

For example: This WEG CFW500 AC Drive from Factory Automation large enough to run a 3HP motor only cost $324 (without any programming).

WEG CFW500 AC Drive, 3HP, 230V 1 PH/3 PH Input, 230V 3 PH Output, 10FLA, includes Braking Transistor, IP20
https://www.factorymation.com/CFW500B10P0B2DB20
​

I'm not doubting you're ability to cover the cost, but wondering if the VFD programming makes it that much more expensive? Just wondering in case someday my old VFD (or motor) goes out on my Vicmarc VL300 Lathe.

Not all VFD's are created equal. There are some bottom of the barrel units that are basic V/Hz without any feedback from the motor. Some units have the ability to do an "auto tune" so that you do not need to know all of the motor performance parameters nor go through manual programming to optimize the motor performance. Better units employ what is called "sensorless vector" which basically senses motor current to make a smart estimate of speed. The high end inverters use true vector feedback from an encoder or tachometer mounted on the motor shaft. Then there are other bells and whistles such as an LCD display that makes it a lot easier to set up the device with plain language rather than cryptic terminology. Some inverters allow you to use a remote keypad or in an industrial setting to allow communications with a computer located in a central control room. The simplest inverters don't employ any kind of braking. Better units might use a braking resistor or regenerative braking.

Some places sell you a VFD, but no tech support or mediocre tech support which is fine if you are already very knowledgeable about setting them up.

 

[Bill Boehme]

While I've not seen a Stubby 750 in person, from the pics, it looks like there is no mechanical gearing. Hence speed control is entirely via VFD.

Is that correct?

Well pulleys and belt is mechanical gearing.

 

[Mike Johnson]

Depending on which drive you purchase your technical support can end up being someone half way around the world reading off of a script with absolutely no electrical or VFD field experience.

 

[Karl Loeblein]

Not all VFD's are created equal. There are some bottom of the barrel units that are basic V/Hz without any feedback from the motor. Some units have the ability to do an "auto tune" so that you do not need to know all of the motor performance parameters nor go through manual programming to optimize the motor performance. Better units employ what is called "sensorless vector" which basically senses motor current to make a smart estimate of speed. The high end inverters use true vector feedback from an encoder or tachometer mounted on the motor shaft. Then there are other bells and whistles such as an LCD display that makes it a lot easier to set up the device with plain language rather than cryptic terminology. Some inverters allow you to use a remote keypad or in an industrial setting to allow communications with a computer located in a central control room. The simplest inverters don't employ any kind of braking. Better units might use a braking resistor or regenerative braking.

Some places sell you a VFD, but no tech support or mediocre tech support which is fine if you are already very knowledgeable about setting them up.

Bill, This is why I specifically linked to a WEG CFW500 drive (see Emiliano first post) with a breaking resistor for a 3HP motor (50% larger than what's needed for a Stubby 750 with a standard 2HP motor). Still seems like I'm missing something other than what you listed above. WEG is a decent VFD company so programming shouldn't be near as hard as the cheaper drives coming from China. Thus, the $1800 price from Omega still has me scratching my head.

 

[Emiliano Achaval]

Bill, This is why I specifically linked to a WEG CFW500 drive (see Emiliano first post) with a breaking resistor for a 3HP motor (50% larger than what's needed for a Stubby 750 with a standard 2HP motor). Still seems like I'm missing something other than what you listed above. WEG is a decent VFD company so programming shouldn't be near as hard as the cheaper drives coming from China. Thus, the $1800 price from Omega still has me scratching my head.

Unlike Bill, I'm not a retired Rocket Scientist nor an engineer at a government secret facility. So I had to buy the Weg unit already wired, ready to go, plug and play. The unit is inside a cabinet with a computer fan. Also, I have the pigtail, the remote wired controller with a magnet. And like Bill said, my unit can do all those things, self-tuning, and I'm running it with sensorless vector now. Those of you that feel sorry for how much I have paid, I already made about 4 times
the cost of the whole wired ready to go unit. I feel sorry for some friends in the mainland that work for days on a bowl and only get $75. I would be watching my budget if I have to work for pennies an hour too. Today I got a commissioned job, a Koa bowl for a wedding present. $1400. I can do it in 2 days. According to my engineer friend, with VFD's you get what you pay for. He showed me a VFD with a price tag of $1500, with no shipping, no plastic cabinet, no computer fan, no pig tail. And that wasnt even the most expensive... About torque, I want to be able to take a full cut on wet Koa with my 3/4 Thompson Bowl gouge. Now, I can stop the lathe with not even half a cut... I want to be able to rough a 20 inch bowl in minutes, not one hour. I want to be able to take 3 or 4 cores with the McNaughton, in minutes, now, I can't... I have been making lots of boxes, the lathe is working ok for small things, no frustration.

 

[olaf Vogel]

Well pulleys and belt is mechanical gearing.

I agree, but thats why I was implicitly asking - not having seen the lathe in person, and I can't tell from the pics if it has mechanical gearing.
Also Emiliano has not mentioned belts slipping.

 

[olaf Vogel]

About torque, I want to be able to take a full cut on wet Koa with my 3/4 Thompson Bowl gouge. Now, I can stop the lathe with not even half a cut... I want to be able to rough a 20 inch bowl in minutes, not one hour. I want to be able to take 3 or 4 cores with the McNaughton, in minutes, now, I can't... I have been making lots of boxes, the lathe is working ok for small things, no frustration.

Like you, I do a lot of big pieces, where hogging out large amounts material, in short time, is important.
So I use very aggressive cuts, which can slow (or even stall) the motor.

(1) My first solution was to match the motor rpms with my required RPMs. That means I don't need to turn the VFD down, which is where I lose a lot of torque. I swapped a 1750 motor for a 1150 then finally a 900 rpm. Now I get 100% rated power at my regular speed. This is why I was asking if you frequently turn down the VFD to get the desired RPMs

This solution means that no external, or additional gearing is required
(Yes, this means my maximum RPMs are limited. But I can run the VFD at 120 hz, which gets my top rpm back.)

Now, if you have internal gearing to achieve this....but I assume you've already done that

(2) I played with different rated horse power motors until I found what worked best for me. And that was 5 hp. It lets me take all but the most ridiculous cuts, without stalling or slowing,

(all of this was with the same VFD. Its possible your VFD is less than your needs....but not that likely)

So as for motor options (like you, I have a mounting issue which limits my motor options)

It looks like the Stubby uses a c-face mounted motor, so your motor options "may" be limited in terms of the above.
If thats the case, there still may be options. Rather than bolting the motor face to the lathe, you could mount the motor externally and mechanically extend the shaft so that it bolts up to the jackshaft inside your headstock. (sorry thats not a great explanation and I can elaborate if you wish)

Hope that helps

 

[Bill Boehme]

I agree, but thats why I was implicitly asking - not having seen the lathe in person, and I can't tell from the pics if it has mechanical gearing.
Also Emiliano has not mentioned belts slipping.

OK, I get your point now. Several years ago a friend had a similar problem with his Vicmarc lathe stalling at low speed. I asked him which position the belt was in and he said the high speed position. That was the problem. When he put the belt in the lowest speed position there was plenty of torque.

@Emiliano Achaval I thought that you already had the new VFD and motor installed and all was well. Are you still waiting on parts?

 

[Karl Loeblein]

... I feel sorry for some friends in the mainland that work for days on a bowl and only get $75. I would be watching my budget if I have to work for pennies an hour too. Today I got a commissioned job, a Koa bowl for a wedding present. $1400.

Yes, I'm one of those mainland guys which only gets $75 a bowl which is why I'm not quitting my day job. Only trying to understand why your new VFD cost more than my used Vicmarc Vl300 lathe is all. Here's hoping my old VFD & motor has many more years left on them.

 

[Emiliano Achaval]

Like you, I do a lot of big pieces, where hogging out large amounts material, in short time, is important.
So I use very aggressive cuts, which can slow (or even stall) the motor.

(1) My first solution was to match the motor rpms with my required RPMs. That means I don't need to turn the VFD down, which is where I lose a lot of torque. I swapped a 1750 motor for a 1150 then finally a 900 rpm. Now I get 100% rated power at my regular speed. This is why I was asking if you frequently turn down the VFD to get the desired RPMs

This solution means that no external, or additional gearing is required
(Yes, this means my maximum RPMs are limited. But I can run the VFD at 120 hz, which gets my top rpm back.)

Now, if you have internal gearing to achieve this....but I assume you've already done that

(2) I played with different rated horse power motors until I found what worked best for me. And that was 5 hp. It lets me take all but the most ridiculous cuts, without stalling or slowing,

(all of this was with the same VFD. Its possible your VFD is less than your needs....but not that likely)

So as for motor options (like you, I have a mounting issue which limits my motor options)

It looks like the Stubby uses a c-face mounted motor, so your motor options "may" be limited in terms of the above.
If thats the case, there still may be options. Rather than bolting the motor face to the lathe, you could mount the motor externally and mechanically extend the shaft so that it bolts up to the jackshaft inside your headstock. (sorry thats not a great explanation and I can elaborate if you wish)

Hope that helps

This is very helpful. I do change the position of the belt all the time. I need speed for boxes and high torque for big bowls. I have to wait 4 to 6 weeks for a new motor, it's been ordered. I wish you or @Bill Boehme Boehme would come to Maui, I have a room for you guys. I’m judging the lathe performance by how she was running up to last year. The McNaughton was not able to stop the motor. Now, I was cleaning the chuck with a 3M pad, and I can stop the lathe by hand! I'm guessing 95% of turners never have to worry about this problem. If they do, they don't have to deal with shipping times, and a lack of places that can deal with the problem on a small island. Is the price we pay to live in paradise surrounded by Koa and Milo.

 

[Bill Boehme]

This is very helpful. I do change the position of the belt all the time. I need speed for boxes and high torque for big bowls. I have to wait 4 to 6 weeks for a new motor, it's been ordered. I wish you or @Bill Boehme Boehme would come to Maui, I have a room for you guys. I’m judging the lathe performance by how she was running up to last year. The McNaughton was not able to stop the motor. Now, I was cleaning the chuck with a 3M pad, and I can stop the lathe by hand! I'm guessing 95% of turners never have to worry about this problem. If they do, they don't have to deal with shipping times, and a lack of places that can deal with the problem on a small island. Is the price we pay to live in paradise surrounded by Koa and Milo.

Buy my plane ticket and I will hand carry (well actually my back problems prevent me from carrying anything that heavy, but I'll let you hand carry ...) a three horsepower Baldor industrial motor. The motor is rated for inverter duty from 0 (that's a zero) to 6,000 RPM (you would have to be crazy to run it that fast). It weighs about 88 pounds. It can deliver constant torque from 0 to 1750 RPM and constant HP from 1750 to 6000 RPM. The only gotcha is that it requires a VFD that is capable of using optical encoder feedback. I have a couple Baldor 2 HP inverters that use encoder feedback, but not one for a 3 HP motor.

I had thoughts of using it on my Robust, but the frame size won'r fit the headstock opening.

 

[Doug Rasmussen]

Do you have visual access to the VFD readout on the Stubby? It'd be interesting to see the frequency on the VFD readout when the spindle slows under load.

Are you 100% certain the belt is not slipping or that the motor or spindle pulleys are not loose (spinning) on their shafts? Do either of the pulleys feel unusually hot to the touch when the spindle is slowed under load??

Is the motor speed noticeably slowing as the spindle slows? You should be able to judge somewhat about motor rpm as the spindle nears stalling just by feeling the motor. If it's a totally enclosed motor there may ventilation slots on the end fan cover you can see into with a flashlight to verify motor is stalling along with the spindle.

 

[Emiliano Achaval]

Do you have visual access to the VFD readout on the Stubby? It'd be interesting to see the frequency on the VFD readout when the spindle slows under load.

Are you 100% certain the belt is not slipping or that the motor or spindle pulleys are not loose (spinning) on their shafts? Do either of the pulleys feel unusually hot to the touch when the spindle is slowed under load??

Is the motor speed noticeably slowing as the spindle slows? You should be able to judge somewhat about motor rpm as the spindle nears stalling just by feeling the motor. If it's a totally enclosed motor there may ventilation slots on the end fan cover you can see into with a flashlight to verify motor is stalling along with the spindle.

We did it a hundred times, I was turning and my engineer friend was sitting in front of the VFD, looking and taking notes. My motor is totally enclosed. We did open it to see inside. Looks brand new. Belts are not slipping... Thank you Doug.

 

[Emiliano Achaval]

Buy my plane ticket and I will hand carry (well actually my back problems prevent me from carrying anything that heavy, but I'll let you hand carry ...) a three horsepower Baldor industrial motor. The motor is rated for inverter duty from 0 (that's a zero) to 6,000 RPM (you would have to be crazy to run it that fast). It weighs about 88 pounds. It can deliver constant torque from 0 to 1750 RPM and constant HP from 1750 to 6000 RPM. The only gotcha is that it requires a VFD that is capable of using optical encoder feedback. I have a couple Baldor 2 HP inverters that use encoder feedback, but not one for a 3 HP motor.

I had thoughts of using it on my Robust, but the frame size won'r fit the headstock opening.

Wish I could use your Motor! I was told my VFD could run a 3HP motor, but not to its full potential, is that right?

 

[Bill Boehme]

Are you 100% certain the belt is not slipping or that the motor or spindle pulleys are not loose (spinning) on their shafts? Do either of the pulleys feel unusually hot to the touch when the spindle is slowed under load??

Good things to check, especially the pulley slipping. Some pulleys have a keyway and the key could have fallen out or even sheared. More likely it would be a setscrew (grub screw if you live in Oz) that has loosened due to vibration. Thanks for looking for the obvious first. We may have prematurely jumped to conclusions.

A slipping belt usually squeals and for sure will get the pulley hot.

So what did the VFD say when the spindle stopped? I don't think that looking at the VFD would tell you much if anything since it is just outputting a frequency, but doesn't know what the motor is doing. Maybe it's the motor pulley that is slipping, but the motor is running at the commanded speed. if you haven't done it already look at the motor shaft while holding the spindle so it doesn't turn.