Critique Requested for 11 Pound Water Cooled VFD Motor in Testing on 2 x 72 Grinder

[Drew Riley]

Interesting. I'd be curious to see how the motor and small drive wheel handled a larger load, or really bearing hard into something like a flat platen that has a lot of surface contact.

 

[Geoff Flato]

Trust me you can. I could stall out my 9000sfpm 2hp grinder, that’s why I dropped the rpm so I could bump if the torque. It all comes down to surface area. If your just profiling thin blade steel then it’s hard but as soon as you move from a wheel to a platten and start flat grinding then it’s a different ball game. Geoff maybe something like this bad boy, 7.5hp Baldor. Got it for free becaus the bearing where shot. $15 and she is good as new, would make a hell of a grinder lol

That'd do well!
I love my Bee, but I'm wanting to build something for hogging, profiling, rough beveling, ect. I can stall 2hp at 5600 sfm without all that much trouble.

I'm planning on basically a straight clone of my Bee, only with bigger drive wheel and motor.

 

[javand]

You guys would see a big difference with a quality 3hp motor. 5hp is overkill IMO without leverage assist.

FWIW, I haven't met a 2hp grinder I couldn't stall (especially any running on 110V input with a KBAC 27D or similar, which only produces about 1.5hp, regardless of the motor rating), but my 3hp, 1700 RPM Baldor with 2X jumper on a KBAC 29, obviously with 220V input, and a 6" poly coated drive wheel, I can not stall by hand. Even flat grinding a 16" 52100 bowie with a giant push stick, leaning into it as hard as I could. Course, this is a high torque VFD rated motor.

HP ratings on electric motors are very deceptive, and often do not correlate with real world power.

As an example, the 7.5hp 800 RPM motor on my Bradley stap hammer, weighs around 400 lbs, and is about the size of a typical 30hp motor.

Another thing to consider however, is that a lot of times it's a combination of drive wheel slip for non-coated wheels and stalling, and overheating those motors, especially on slower speeds.

 

[JTknives]

My blue 7.5hp is 1175rpm and is like 300lbs. It’s almost as big as the huge 25hp Toshiba I just bought

 

[BelnapCustomKnives]

It’s not that I did not like the high speed, it was that it came at a reduced torque penalty. With fresh sharp belt yeah it hauled ass but once the belts started to wear and you needed to really lean on the steel the grinder would have issues. So like I said if I could have say a true 5hp and go from about 1000sfpm up to around 9000sfpm it would be perfect. But the other issue is vibration and noise level has a tendency to go way up when in the higher ranges. I love a quiet grinder. So maybe your on to something if it truly has low sfpm preformance. I’m going to be building another grinder soon and had planned on it being a smaller grinder set up like travis mini. Would just be for hallow grinding. But my design requires a motor that’s stout enough to support the entire grinder on the shaft. But I could see potential for a high HP hogging grinder that is wicked smooth. It could even be set at one SFPM and just left there as it would be duty specific.

I saw what you did with the surface grinder and look forward to seeing your solution on your next projects.

I like what you done .With help from my friend in his shop we are half away in building CNC grinder/8000SFPM/ and I was thinking to use same motor as yours .My friend manufacturing big 4x2 meters CNC router for furniture factories and he use this kind of motor,China made . He sell many router and have no complain from user about this spindle motor ....But I give up from this kind of motor .First reason was NOISE .................well that thing/motor/ is really LOUD on high RPM and I live in very urban environment ...... Second reason was drive wheel .........considering that motor have very high RPM must be used very small drive wheel and I was concerned that belt would slip on drive wheel , small contact area on drive wheel with belt .But now I see that small drive wheel can work... you have now put me in doubt .maybe i will use spindle motor My current belt grinder /two wheel and 2x42 inch belt / run on 6450 SFPM and I like it ...................
Today I start to work on another small grinder /2x42 belt/ will run in range of 2000/ 8400 SFPM ........ + small wheel and max. 12 inch wheel attachment
I posted here for another point of view to see what additional things I can try with this little motor. I also had the same worries as everyone else has expressed here. But decided to try it to the best my design skills would allow. I have been very surprised by the performance so far. That tiny wheel I also worried would slip. You can see in this video that the wheel does not slip under very heavy load and high speed.

running 7000 SFPM under heavy full width belt load. Also this is not a brand new belt. This belt has already ground 30 previous blanks so it is as real world test as I have been able to do. It is exactly how I grind. 3M belts like it this way. This little motor seems to love it as well. It is an uphill battle. It is hard for me to believe because it seems to be against most design logic I have always used. That is why I posted here to find out other ways to test it hard.

I think that you wasting time talking with guys here about high speed grinder ... they don t like screaming fast grinder .........I have no idea why
Thank you for showing your grinder ..........

 

[BelnapCustomKnives]

It’s not that I did not like the high speed, it was that it came at a reduced torque penalty. With fresh sharp belt yeah it hauled ass but once the belts started to wear and you needed to really lean on the steel the grinder would have issues. So like I said if I could have say a true 5hp and go from about 1000sfpm up to around 9000sfpm it would be perfect. But the other issue is vibration and noise level has a tendency to go way up when in the higher ranges. I love a quiet grinder. So maybe your on to something if it truly has low sfpm preformance. I’m going to be building another grinder soon and had planned on it being a smaller grinder set up like travis mini. Would just be for hallow grinding. But my design requires a motor that’s stout enough to support the entire grinder on the shaft. But I could see potential for a high HP hogging grinder that is wicked smooth. It could even be set at one SFPM and just left there as it would be duty specific.

I will do some slow testing. My initial bevels are done fast with a guide then I slow down and finish from there. I saw your surface grinder mod. Looking forward to seeing your next project.

 

[BelnapCustomKnives]

Trust me you can. I could stall out my 9000sfpm 2hp grinder, that’s why I dropped the rpm so I could bump if the torque. It all comes down to surface area. If your just profiling thin blade steel then it’s hard but as soon as you move from a wheel to a platten and start flat grinding then it’s a different ball game. Geoff maybe something like this bad boy, 7.5hp Baldor. Got it for free becaus the bearing where shot. $15 and she is good as new, would make a hell of a grinder lol

This video is of the little motor running at 7000 sfpm using a bevel guide to apply full width pressure. The belt has already ground 30 blanks so it is not brand new. The little motor handled it well in my opinion.

I would run the motor for sets of five blanks straight then I had to take a break and the motor was just warm. The water cooling kept it at a low operating temp even after an hour of continuous hard operation.

 

[BelnapCustomKnives]

I think it's a horrible idea myself to be perfectly honest.
Look at what a reputable name brand spindle motor costs in comparison to that thing? Hell just a good conventional drive would cost more than that whole setup. You know major corners had to be cut.
I'll be surprised if it doesn't blow up eventually.
Needlessly complicated, an obvious sacrifice of reliability, and for no benefit. This honestly sounds like one of the things you see in beginners groups on Facebook where people are too cheap to buy a proper tefc motor and KB drive.
If I wanted higher speed (my grinder runs from 1100 to 5600 sfm, and I run it wide open for ceramic belts) I would be going the opposite direction from what you have, and use a large drive wheel. A big thing turning slowly will always be more reliable and durable than a tiny thing spinning stupid fast. I'm sure this thing will work great for you, until it let's the magic smoke out or blows up like a grenade.

I also agree with your design logic. This thing is really surprising me too. I am waiting for it to blow or choke. I hoped this would register higher that noob level of design lol. I did design and build the entire drive assembly including that wicked little wheel that many thought would just slip on the belt at those speeds and loads. But still a noob move I guess.

 

[BelnapCustomKnives]

I love a fast grinder, and have nothing against it provided speed doesn't come at the cost of reliability, tracking, or being smooth and quiet. Its the chinese spindle motor I don't like about this. For what its worth, I do plan on building a grinder that will go to 7-9000 at some point, but it will have a conventional 5 or 7.5hp motor driving it.

You'd never see high speed motors used for this in industry. And there is a reason for that.

How about for a compact frame machine that is mobile?

 

[BelnapCustomKnives]

I love a fast grinder, and have nothing against it provided speed doesn't come at the cost of reliability, tracking, or being smooth and quiet. Its the chinese spindle motor I don't like about this. For what its worth, I do plan on building a grinder that will go to 7-9000 at some point, but it will have a conventional 5 or 7.5hp motor driving it.

You'd never see high speed motors used for this in industry. And there is a reason for that.

Tracks well

 

[BelnapCustomKnives]

Last time I checked it seamed going with a DC motor and nema 4 speed control was cheaper than my current AC with nema 4.

Thanks for commenting.

 

[BelnapCustomKnives]

Thank you to everyone that commented. Believe it or not it was all very enlightening and helpful. I was already aware of the many worries that many expressed and the verdict is still out on the longevity of the setup. That should be understood as part of the ongoing development process. What I did learn that I did not know is that the conventional motor VFD 2-3hp die out under heavy removal load if they are run at 7000 sfpm. This was mentioned by two people and they felt this rendered those conventional motors ineffective for heavy removal at those speeds. Also that if you setup a conventional motor to operate at 7000 sfpm it will not run well at the low end because the drive wheel it too large to let it develop much torque at the lower speeds and to effectively run at lower speeds a smaller wheel would be required. I did not know these things before. From my limited experience so far with this motor and drive it has been able to perform well under heavy removals at speeds from 5000 to 7000 sfpm. It really likes running at 7000 sfpm. Below these speeds working pressure would reduce to medium then as the speed dropped to around 1500 sfpm would be able to sustain light pressures on the belt. Due to the very small drive wheel the belt can be slowed down very very slow and still be effective. Not sure if the conventional motor would have the capability to run the belt so slow. I will video this soon when the heavy removal phase is complete and I begin to detail the blanks. For me and the way I grind these are perfect for the spread of power and speed. I use all available power for top end high speed heavy removal, then slow and do some refining work in the mid range before slowing further and detailing with light pressure. I have been able to use scotchbrite belts with no issue. As this batch progresses I will use the leather belt to polish the cutting edge.
A Leeson (Made in China) 2HP 3 PH weighs 48 pounds and cost 5 times more while delivering less performance at the belt.

 

[Joshua Fisher]

Belnap take a look at these motors, I have a drill press with the 1.75hp motor in it and have operated a wood lathe with the same motor and have been impressed with it and thinking about using one for a 2x72 they are very quiet and have a good speed range with torque settings for different operations. http://www.dvrsmartmotor.com/motors.html

 

[mike-E]

I have to agree with Natlek on high speed being the way to go. I run an 8" direct drive wheel with 2hp on 2x jumper. I can surface grind .015 deep passes on 1 1/2" wide stock and barely even hear the motor reduce speed. I believe the reason JT had issues running fast is because he was running a pulley set up to get 9k+sfpm.
I am having doubts about the "compactness" of your machine. After adding the special drive wheel set up to the length of your motor I am betting you save less than two inches on width. With such a small drive wheel you are going to have to extend the tooling arm an extra 3-4 inches compared to a 8" drive wheel on the same frame. You may have built it where more of the belt is taken up vertically, but either way, you have 72" of belt to deal with.
I saw Travis`s grinder video and I believe he is running some type of little timing belt on the motor to drive set up.
What I noticed about both his and yours is the speed reduction when pressure is applied to the grind. Just as a guess, it sounds like 25-30% drop. I think you will be surprised if you get a tach measurement while actually grinding and see how much speed loss you are getting.
Your grinder is doing one great job of removing steel fast. That much is obvious. I am just curious about the longevity of not just the motor/drive, but also the bearings on the drive wheel set up. How hot are those things getting after a grinding session?
Also what is the point of wanting to save 20-30 pounds on the motor? Are you planning on going mobile? If so, I can see a slower set up being useful as a sharpening business machine, but that's about it. I think you are trying to reinvent the wheel. jmho.

 

[mike-E]

I didn't want to edit, so I'll just post a second time with extra critique. How much space and weight are you saving if you factor in the water pump, the coolant resevoir, the extra electric, water lines, and all the area it takes to secure these things? How much space and weight could you actually save if you went with a direct drive and 8" wheel?
You say this type of motor is 5 times cheaper than a regular Chinese 1800 rpm motor. I think you can still buy a Chinese motor from automation direct for much less than $200. Are these motors really $30-40 when bought separately?
I also saw that you have already experienced bearing failure at the exact place I would have expected. The outside bearing on the drive setup. I think that is going to be the consistent point of downtime. Also that type of failure at high speed is often going to cost you either a destroyed wheel or housing as well as a bearing set.

 

[BelnapCustomKnives]

Belnap take a look at these motors, I have a drill press with the 1.75hp motor in it and have operated a wood lathe with the same motor and have been impressed with it and thinking about using one for a 2x72 they are very quiet and have a good speed range with torque settings for different operations. http://www.dvrsmartmotor.com/motors.html

Thanks.

I didn't want to edit, so I'll just post a second time with extra critique. How much space and weight are you saving if you factor in the water pump, the coolant resevoir, the extra electric, water lines, and all the area it takes to secure these things? How much space and weight could you actually save if you went with a direct drive and 8" wheel?
You say this type of motor is 5 times cheaper than a regular Chinese 1800 rpm motor. I think you can still buy a Chinese motor from automation direct for much less than $200. Are these motors really $30-40 when bought separately?
I also saw that you have already experienced bearing failure at the exact place I would have expected. The outside bearing on the drive setup. I think that is going to be the consistent point of downtime. Also that type of failure at high speed is often going to cost you either a destroyed wheel or housing as well as a bearing set.

The Leeson 2hp 3ph is a chinese made motor. This is a very common one used on sanders. It is around $900.00 but some places it can be found for some less and they are still 3 times the price of the spindle. I mean to compare to this type of motor not just a cheap motor. This is the motor I am comparing against. https://beaumontmetalworks.com/product/3-hp-variable-speed-motor-and-controller-copy/

 

[BelnapCustomKnives]

I have to agree with Natlek on high speed being the way to go. I run an 8" direct drive wheel with 2hp on 2x jumper. I can surface grind .015 deep passes on 1 1/2" wide stock and barely even hear the motor reduce speed. I believe the reason JT had issues running fast is because he was running a pulley set up to get 9k+sfpm.
I am having doubts about the "compactness" of your machine. After adding the special drive wheel set up to the length of your motor I am betting you save less than two inches on width. With such a small drive wheel you are going to have to extend the tooling arm an extra 3-4 inches compared to a 8" drive wheel on the same frame. You may have built it where more of the belt is taken up vertically, but either way, you have 72" of belt to deal with.
I saw Travis`s grinder video and I believe he is running some type of little timing belt on the motor to drive set up.
What I noticed about both his and yours is the speed reduction when pressure is applied to the grind. Just as a guess, it sounds like 25-30% drop. I think you will be surprised if you get a tach measurement while actually grinding and see how much speed loss you are getting.
Your grinder is doing one great job of removing steel fast. That much is obvious. I am just curious about the longevity of not just the motor/drive, but also the bearings on the drive wheel set up. How hot are those things getting after a grinding session?
Also what is the point of wanting to save 20-30 pounds on the motor? Are you planning on going mobile? If so, I can see a slower set up being useful as a sharpening business machine, but that's about it. I think you are trying to reinvent the wheel. jmho.

thanks. I have been wanting to put a tach on it to test the speed under load.

 

[BelnapCustomKnives]

I didn't want to edit, so I'll just post a second time with extra critique. How much space and weight are you saving if you factor in the water pump, the coolant resevoir, the extra electric, water lines, and all the area it takes to secure these things? How much space and weight could you actually save if you went with a direct drive and 8" wheel?
You say this type of motor is 5 times cheaper than a regular Chinese 1800 rpm motor. I think you can still buy a Chinese motor from automation direct for much less than $200. Are these motors really $30-40 when bought separately?
I also saw that you have already experienced bearing failure at the exact place I would have expected. The outside bearing on the drive setup. I think that is going to be the consistent point of downtime. Also that type of failure at high speed is often going to cost you either a destroyed wheel or housing as well as a bearing set.

Thanks. The failure was the actual drive wheel. The same bearings were reinstalled after the wheel failure. The wheel failed in this instance because of machining tolerance too large and assembly method was poor. The second wheel is installed better and has yet to show signs of failure. I also suspected a failure there so that I why I made 5 wheels so I could try some different methods.

 

[JTknives]

Yeah part of my problem was the pull setup I was using to bump the speed to the higher umbers. I have a small 1hp 3ph motor that I’m putting on my mill that says 1775rpm but then says max 6000rpm. It’s designed to be used on a vfd. If I could snag one of these in a larger HP rating I would be more then happy. The problem with VFD and motors is torque and hp. If you run at name plate rpm you get the nameplate hp. But as soon as you use the vfd to drop the rpm you loose HP but it try’s to keep torque. This is becaus motors have a voltage to HZ ratio. If you go over this ratio then the stator becomes saturated and does not work. So as you drop the speed which is HZ the vfd must drop voltage to keep the V/HZ ratio corect. If you go the other way and speed a motor up the vfd can’t put out more voltage then it’s given so it keeps the voltage at the 240v and just increases the HZ. What this does is increases RPM but keeps HP at the name plate rating. But this comes with a drawback and that is a drop in torque. Here is a chart that might make a little more sence.

 

[BelnapCustomKnives]

Yeah part of my problem was the pull setup I was using to bump the speed to the higher umbers. I have a small 1hp 3ph motor that I’m putting on my mill that says 1775rpm but then says max 6000rpm. It’s designed to be used on a vfd. If I could snag one of these in a larger HP rating I would be more then happy. The problem with VFD and motors is torque and hp. If you run at name plate rpm you get the nameplate hp. But as soon as you use the vfd to drop the rpm you loose HP but it try’s to keep torque. This is becaus motors have a voltage to HZ ratio. If you go over this ratio then the stator becomes saturated and does not work. So as you drop the speed which is HZ the vfd must drop voltage to keep the V/HZ ratio corect. If you go the other way and speed a motor up the vfd can’t put out more voltage then it’s given so it keeps the voltage at the 240v and just increases the HZ. What this does is increases RPM but keeps HP at the name plate rating. But this comes with a drawback and that is a drop in torque. Here is a chart that might make a little more sence.

I did not know this relationship. The chart helps. I did not see an HP, HZ, Torque chart for the little motor. It is advertized as a 3hp, 400hz. Would it possibly mean than at 400 hz it is developing full 3 hp and not like the 60 hz motor that begins to loose hp once the hz go over 60 to increase rpm? Now I really want to see a chart like this specific to the spindle motor to understand the relationship for that motor. If it was the case that the small motor is developing full hp at 400hz that might explain why it is doing well and also why so many people say it should not do well because they are used to seeing a 60hz motor chart where hp drops above 60hz?