Spindle motor rewinding - do or don't?

Hey Guys!
One of the Fadals that I'm currently rebuilding let the magic smoke out of the drive and spindle motor today... They were acting a little funky before but I didn't realize how bad things were out of whack and before I know it the motor was too hot to touch...

Cooled it down as quick as I could and then checked it with a megger, sure enough it reads practically zero from the windings to ground. I said some nasty words when I saw that as I'm sure you can imagine. Not really sure if it was the drive that took out the motor, or whether the motor went bad and took out the drive, but either way they're both toast now!

A replacement spindle motor (5HP) is USD$1,600 which isn't too bad, but shipping and import duties from the US are going to bring that up to north of CAD$2,500.

There are a couple of motor winding shops around me and one of them looks pretty nice. Will having a motor rebuilt result in something that's 'good as new' or does it result in something second rate? Should I go get this motor rebuilt, or just scrap it and get a new one?

Thanks!
-Aaron

Hey Aaron,

That's some bad luck but this is the type of stuff that comes up with used machines.

A few years ago the spindle motor and drive on my Haas had the same type of thing happen. I removed the spindle and had it checked out at a local electrical shop. They said it was gunked up with dried coolant and after cleaning it up it checked out fine. It's been running fine for 4-5 years now, albeit sparingly. They also mentioned that for motors 10hp or less it's cheaper to buy a new one than to repair it, don't know if that's true. As for the spindle drive, luckily my brother is an electrical whiz and was able to fix it, I forgot what the issue was, capacitors or something.

For a 5hp motor, I'd call some of those electrical shops and see if they have a replacement unit. You'll need to give them the model number on the motor tag. The numbers might not make sense but they know how to decipher them. I can't imagine a new 5hp motor would cost $2000+, especially for a Fadal, which is nearly made from generic items you can buy from McMaster. I know you're out in the east end of Toronto but if you need a good place to bring the motor to, check out Magneto Electric. They're in Mississauga, near Dixie and Eglinton. They ain't cheap though but they know what they're doing.

Good luck!

Thanks for the feedback mate! Yeah I got unlucky this time, that's ok hopefully it will get sorted soon enough and I can move on to getting this machine back together!

Good idea to get some local quotes for the motor, I had only looked at prices from Fadal parts suppliers and they all want about $1600 US for a new one.

I think the drive itself is likely toast, it's a very old Baldor which wasn't powering on the programming keypad properly right from the start so something has gone screwy with it. I have already replaced one older drive on another machine with a new Glentek drive and was very happy with that. Installation was literally 15 minutes and it worked perfectly right from the start, unlike some other screwy 'replacements' I have tried from others sellers who shall not be named

I might have a poke around inside it tomorrow but I don't have high hopes... The older SCRs in these drives seem to be hard/expensive to source from what I've seen during past experiences.

Just, as in a few months ago, had a 7.5 hp saw motor rewound. silky smooth acceleration and deceleration now. A few years ago had a 25 hp crane motor rewound. Has power, deceleration is not to perfection but dang close. Looked back when we had that one redone, the crane in same bay was rewound over 20 years ago, so good life so far. Same motor shop did all three.

Just curious..tell me about this silky smooth deceleration. Isn't it merely coasting to a stop or is this some hi-tech setup? I've had many a simple 3 phase motor rewound and there was nothing special about the motor, post-rewind.

Stuart

oh, vfd on every motor in shop minus roof fans, which are to be replaced next upgrade. the saw decelerates, then decelerates slower, then decelerates. All within .25 seconds- when you do something enough you hear everything.

When I have a motor rewound they give it a higher isolation class as standard
Just to be on the safe side
So yes you can call a rewound motor better then

Peter

I probably have had at least a dozen motors rewound over the course of owning my small shop for over 20 years. A good motor rewind shop comes in real handy. When I was on the left coast I had a place that repaired them fast and at a reasonable price. Motor rewind shops run the gamut on pricing and quality.

I just got a rough quote from a shop that's just down the street, they reckon about $650 (Canadian) for a rewind and new bearings which seems very reasonable. Buying a new one from the USA would be about $2,700 Canadian including shipping and import duties. Ouch, looks like I'll be trying a rewind!

Didn't realize this was actually a 10HP motor, not a 5HP like the one on my VMC10. Seems the VMC15s actually did get a little upgrade from the VCM10. I thought they were identical (other than the lack of enclosure on the VMC10) so that's good to know!

I have a lot of experience with electric motor repair shops. I consult to many of them.

A quality shop will have no issues rewinding the stator - rewinder will probably use a vfd duty rated wire, which in most cases should be fine.

The differentiation is in the mechanical world. Most shops cannot even measure the bearing fits properly, not to mention restoring them correctly. I don't know what speed your motor is, but getting a good balance on a spindle motor can be a challenge, especially on a high speed spindle motor. Most balance machines in repair shops are limited to somewhere around 600 rpm balance speeds.

One option is that you do the mechanical work yourself and have them just rewind it, or ask the proper questions and get comfortable with their mechanical work. If you are concerned about balance, you can just leave the balance of the rotor as is - you might make it worse if you try to rebalance. All in the shop's capabilities.

For us, for a standard NEMA motor, we generally do not fix any motor up to 200 hp even if it needs just bearings. For us its just not worth it. Not the case in this situation. But because of this, many quality motor repair shops do not want to work on motors that are under a couple hundred hp.

markz528 said:

The differentiation is in the mechanical world. Most shops cannot even measure the bearing fits properly, not to mention restoring them correctly. I don't know what speed your motor is, but getting a good balance on a spindle motor can be a challenge, especially on a high speed spindle motor. Most balance machines in repair shops are limited to somewhere around 600 rpm balance speeds.

Click to expand...

This is very important. Make sure that they understand that this is a precision spindle that is being rebuilt. I have a local electrical place that I will take most general electric motor things to. I had them quote redoing a grinder motor (it mounts on the spindle) and just based on their quote I knew I did want them doing the work. When I went by the shop, there was no clean room. How do you assemble high precision bearings in a filthy shop?

You might split the job up, rewind in one shop, spindle rebuild and balance in another. I would think any of the spindle rebuild shops could do the job. Some may be willing to rebuild the spindle and in their facilities marry the stator with the rotor, which would minimize the problem of he said, she said if something go well.

Tom

One thing worth clarifying: this is not an integral spindle motor, this is a separate motor for a belt-driven cartridge spindle. Max speed is 7500RPM so not particularly onerous there. I will talk to them regarding balancing and see what their response is...

With regard to balancing. AFAIK balancer speed has nothing to do with getting even a reasonably high speed rotor balanced properly. Many balancers have their accelerometers calibrated and mapped up to 600 rpm using a calibration rotor with a known unbalance. That's why balancing is done at 600 rpm. I'm not a balancing expert, but that's how we do it and have had excellent results.

650 is a good price on the rewind Aaron. Go that route, and give it a try.
If you need to, there is a really good balancing shop in cambridge that has done a bunch of stuff for me over the years.
They've done everything from driveshafts for my race car to shafts for the Bruce

Or I could put you in touch with the shop that has rewound a number of spindle motors for me, in Stratford.

What is the rated nameplate speed of the motor?

I am not a vibration expert (know people that are) but I know a little bit. Most of the time 600 rpm is adequate to balance a rotor. But sometimes its not. Can't tell you all the times its important to balance at running speed, but just dealt with a couple thousand hp 3600 rpm motor. Balanced just fine twice at 600 rpm but when installed was a paint shaker. Ended up field balancing at speed to correct the problem. I believe that this is probably a flexible rotor and that why it needed balancing at speed (critical speed blow running speed). Will also tell you that the quality driveshafts in our race cars are balanced at speed - mine was balanced at 7000 rpm and the first critical is substantially above 7000 rpm. Cheap driveshafts are balanced at 600 rpm and its usually adequate.

If this is a 3600 rpm or slower motor then I believe that 600 rpm balance is probably ok if done correctly to a very precision balance. If the motor rpm is above that and it were mine, then I would want to balance at speed - don't know if its necessary but its just what would make me comfortable.

One test that I do to get some comfort level in the balance quality is to remove the rotor from the balance stand and then check the balance again. IMO it should repeat to at least 25% of the original values.

Once the motor is assembled, vibration needs to be checked. I like to run the motor on an inertia base unbolted, shimmed for soft foot. For a motor like this, 0.01 to 0.02 inches per second peak velocity overall would be reasonable IMO.

I know my Atrump is not a super precision machine, and the top spindle speed is 4200 rpm, but the motor starts resonating above 3500 rpm spindle speed. Not too bad, but it should not be doing it. I will probably re-balance the motor rotor at some point - hopefully that will fix it, otherwise will have to do other changes. Motor is rated at 3600 rpm.

Just a few things from my experiences.

1. Motor shops are rarely equipt to balance beyond base speeds.
2. Your motor almost certainly will run close to spindle speed in high range so between 7000-8000.
3. Having been inside a few cheaper machine spindle motors, including Haas, I would NOT be surprised to see a virgin motor right from the OEM. The rotors are certainly balanced and apparently the MTB thinks that's fine. Get what you pay for.
4. I would have the motor shop "check" the rotor balance before letting them screw it up. I would nearly bet if you just wind it and stick it together, it will work fine for your application. One look at the bearing precision in that motor will tell you just how precise it really is. You will never balance a rotor beyond the precision of the bearings.
5. I would also bet this "spindle motor" is an off the shelf motor that can be found somewhere MUCH cheaper. A Haas in question was a true off-the-shelf Lincoln motor and about 1/2 the HP that was on the huge decal on the front of it.

Dan from Oakland said:

With regard to balancing. AFAIK balancer speed has nothing to do with getting even a reasonably high speed rotor balanced properly. Many balancers have their accelerometers calibrated and mapped up to 600 rpm using a calibration rotor with a known unbalance. That's why balancing is done at 600 rpm. I'm not a balancing expert, but that's how we do it and have had excellent results.

Click to expand...

Also, I thought the OP is only getting the STATOR rewound.
The ROTOR, is not going to be touched ?
So why would a re-balance need be done ?

digger doug said:

Also, I thought the OP is only getting the STATOR rewound.
The ROTOR, is not going to be touched ?
So why would a re-balance need be done ?

Click to expand...

That's a good question actually... Does a re-balance even need to be done if the rotor isn't touched?

For the sake of clarity here is a photo of the motor nameplate:



Nameplate RPM is 1760, I'm sure it's not balanced much past that as my other machines definitely have some vibration up at full RPM (7500).

As others have said I'm fairly sure this is pretty much an off-the-shelf motor from Baldor, Fadal tried to avoid expensive custom parts whenever possible and overall seemed to have done a pretty good job of that.