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Machine Shop and Tool Talk Shop Equipment, fabrication, repairs, how to fix it, which tool to use for the job. Machinist shop talk, straight to the point.

Machine Shop and Tool Talk

Polisher Restoration


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  #41  
Old 04-30-2017, 09:59:08 PM
s100 s100 is offline
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Default Re: Polisher Restoration

The VFD's do produce balanced full power three phase current. As Vanman says, the torque remains the same but as the speed goes down the horsepower decreases. Heavily loading motors at lower speeds can cause cooling issues but in this instance the load is intermittent so the duty cycle will be low, if my polishing attempts are anything to go by. And these motors are very overbuilt. I doubt much will faze them. I doubt they have any cooling fans inside, as the motors, while not sealed (do NOT throw one in a bathtub full of water) are pretty enclosed with not opportunity for cooling air to get inside.

I'm no authority on this, but I too have heard about the spikes caused by VFD's, as mentioned by Beezerbill. They do make "quiet" VFD's for geothermal heat pump use (the regular VFDs generate hash that can interfere with household appliances) but these are considerably more expensive. And it's true that they make "VFD-rated" motors to withstand the spikes caused by regular VFD's. Everything I have been able to learn tells me that this is NOT an issue with old, well built motors but with newer, more cheaply built (non-VFD) motors with less substantial insulation than the old ones. I've had both old and new motors apart and I can easily see substantial difference in construction. I've run several "older" (pre-1960's, don't sound old to me) motors from VFD's and have never had any problems. Did I run them at load for 24 hours a day, seven days a week? No. But I have run them, up to 5HP (I have, among others, a 10HP VFD that, while 3 phase, does not have lost leg detection) and with satisfying results.

Again, this advice, if you choose to call it that, is worth exactly what you paid for it.

Not sure about the transformer systems. I believe these are "start-only" devices that boost the voltage on one leg to unbalance things enough that the motor starts. Commercial capacitor type static converters typically do not include run capacitors because the makers have no idea how much run current the motor being started will draw, so they can't size the capacitor or even take a WAG.

I've owned my small (1HP) Cincinnati for easily 40 years, maybe 50 (time flies). I made a static start/run converter for it back then and have been using it regularly ever since. I used the basic, 100MFD to start, 10MFD to run formula and a potential relay to handle the switching. I have an 8" buffing wheel on one side and a 12" wire wheel on the other. That big wire wheel makes it grunt and ramp up at power-on, causing me to question whether such a machine would start on a single, non-switched capacitor. I can bog the machine down if I'm determined to do so but realistically the machine has plenty of power, and the ability to bog the motor down and possibly stall it is a great safety feature. The big one, 2HP also with a 12" wire wheel on one end, will take things and throw them across the room without so much as a momentary drop in RPM. That one kinda scares me.

Again, since yours doesn't have any proper motor controls, I would seriously consider a small VFD for it. Lots of advantages in a small package.

p.s. Memories are returning, but slowly. If you do buy a 3 phase VFD without lost leg detection s/w, a 1HP VFD will run a 1HP motor from single or three phase. Any larger than that, and you shold derate by 1/3. That is, if you want to run a 2HP motor, for instance, you should have a 3HP 3 phase VFD if you are going to run it from a single phase line, else you will be overloading the diodes.
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  #42  
Old 05-02-2017, 11:21:25 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Polisher Restoration

Monday night I did my best to get as much of the old grease out of the ports that feed the bearings, then packed in new grease. Wired it up to the RPC and engaged the disconnect, she runs, but the bearings were a bit noisy. So this evening I turned it on and let it run about 15 minutes and decided the bearings were running a bit hot, they were not too hot to touch, but definitely much hotter than the bearings on the RPC.

So I pulled it apart this evening, bearing #'s are 3305 , 3605J , and 77206, need to clean the old grease out of them, but none feel bad at this point. One of them does look like a "special" bearing, I believe its the 3605J, it has grooves in outside diameter of outer race, I'm guessing for the grease flow. I'm playing with the idea of replacing bearings with sealed bearings, would I just add ZZ to the numbers?

Sent Cincinnati another email on their online inquiry yesterday, called today and left voice mail, and sent an email thru regular email, maybe I'll hear back from them.
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  #43  
Old 05-03-2017, 09:35:56 AM
beezerbill beezerbill is offline
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Default Re: Polisher Restoration

What trouble was it having running on single phase? I have a VFD on a lathe with single phase input tp the VFD. Originally I ran it off the 208 volt single-phase I have running into my slumlord hole-in-the-wall rental shop. That VFD would not come on at all if the voltage was 207.9 volts but would come on at 208.0 volts. I got a 208 to 220 volt boost transformer on the input and it fixed the problem for good - now always comes on.
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  #44  
Old 05-03-2017, 08:39:14 PM
s100 s100 is offline
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Default Re: Polisher Restoration

I have run several 5HP loads, including a compressor, from my 10HP three phase input VFD without problems. But the compressor, I only ran that to demonstrate it to a buyer. I think a compressor is one application where I would replace the motor with a single phase, "compressor duty" motor or else some old single phase motor. Compressors are demanding loads and I'd want to make sure everything is spot-on. Yes, the VFD has a programmable starting speed ramp-up function and all of the other good stuff but compressors aren't about finesse and features, they're about blunt force stupid brute torque.

In case you are wondering about the "compressor duty" application, a compressor may be expected to make many start stop cycles in any given hour. Modern, ordinary motors are rated for I think 10 starts in an hour. If you're working the compressor hard, you may exceed that. And even with a centrifugal unloader, that's a hard starting load. A regular motor may overheat the starting windings under such conditions. And since the compressor won't run long until it's charged up and shuts off, the cooling air doesn't have a real chance to do its thing.

A brief editorial, if I may. Used to be there were only a few kinds of motors, open, drip prof, totally enclosed, with various mountings. Now there's motors for every sort of use. There's compressor duty motors, VFD duty motors, and who knows what else. Why is this? I say it's because motor designers are working on the very edge today, in order to make their motors as cheaply as possible. Every aspect of the thing has been pared down to a bare minimum with no room for error or overload. The special use motors have been built more robustly in one or more specific areas so they should at least last through the warranty period. That's why when people hear me griping about how cheaply made today's motors are, and they ask what sort of motor they should get, I simply say, "an OLD one."

Meanwhile, back at the ranch, someone was fixing a buffer. There must be some reason why manufacturers always use open bearings on their grinders and buffers, even though it seems to me this is an ideal application for a sealed bearing. I've replaced open bearings in motors and grinders in the past with sealed bearings and have had no complaints or reason to rethink the notion. On a high speed application like this, you have the added benefit of having the right, light grade of grease that will play well with the high speed of your buffer. Plain old chassis grease or disc brake wheel bearing grease is a bit stiff for that kind of speed. And it will be the right quantity. The most common failure mode for ball and roller bearings is over greasing, or so say the manufacturers.
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  #45  
Old 05-03-2017, 09:15:56 PM
Vanman Vanman is online now
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Default Re: Polisher Restoration

I have always just *assumed* that sealed bearings simply didn't exist back then.
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Old 05-03-2017, 09:43:41 PM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Polisher Restoration

For years manual transmissions used open bearings, they switched to sealed bearings even tough they are running in gear oil. I think it's to keep the grit and metal out of the bearings, it seems to have helped them live longer.
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  #47  
Old 05-04-2017, 04:55:49 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Polisher Restoration

Did a bunch more reading on the PM website yesterday on the transformer/autotransfomer phase converter method, I'm thinking that is what I'm going to try. #1 it lets motor produce full power, #2 I can probably put it inside the pedestal, or at least in a box on back of the pedestal,

One of the things I learned was that there are some static transformers that do deliver full power, the Phase Perfect, and the Ronk Add-a-Phase mentioned earlier, and the transformer method. The Ronk design is transformer converter, the Phase Perfect is circuit boards.

The transformer converter is an old design, originally patented in the 40's, it fell out of favor when 3 ph motors became cheaper than transformers, and the RPC is more of a plug and play design. The positive aspect of the transformer converter is they are good at starting hard loads, they have low idle draw, and its quiet. The downsides are that voltages have to be balanced with capacitors for every different motor, and you don't get instant reversing.

I need to get dimensions on the bearings, I'm finding a few NOS bearings with those numbers, but they are not sealed bearings.
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Old 05-04-2017, 05:25:22 PM
Vanman Vanman is online now
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Default Re: Polisher Restoration

I would be interested in reading about the transformer converter. I have only a WAG as to how they may work.

Keith
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  #49  
Old 05-04-2017, 11:24:38 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Polisher Restoration

Keith
Most of what I've read was over at Practical Machinist forum, there are several threads on the subject, but not much hard info. The thread I read yesterday is titled "The Super Fantastic Transformer Method - Amazing To Behold - Stupendous - 8th Wonder", a bit over the top, and the op got flamed on a bit for that title. Like I said, not much hard info but last page or 2 has a couple of diagrams of the wiring, I'm still trying to decipher and digest it.

The "rediscoverer" of this info has a website unique3phase.com and some youtube videos. A lot of his wiring looks a bit disorganized and sometimes scary, but he is running 30 and 50hp motors off single phase so I'm guessing it does work. He has a book on the subject, it was $16 on Amazon, if I learn even 1 thing from it I'll consider it money well spent. I'll let you know what I think about the book next week.

Measured the bearings today
Left side Middle Right
3605J 77206 3305
62mm 62mm 62mm OD
25mm 30mm 25mm ID
1" 16mm 17mm Width

That 1" is correct, but I'm pretty sure 26mm would work too. Any body know bearing numbers? Or willing to give us a primer.

Aargh, it won't let me space those numbers out!
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  #50  
Old 05-05-2017, 12:53:12 PM
s100 s100 is offline
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Default Re: Polisher Restoration

Bearing numbers for old time stuff was the wild west, very few hard standards or consistency between makers. That said, the meat is usually in the last three numbers. The 3605 is an odd duck with no clear cross reference to modern numbering standards, or at least none that I, as a bearing neophyte can discern. The 3305 and the 77206, the important digits are the 305 and the 206. Oftentimes you will find bearings in old stuff that have only those three digits, but sometimes, as in your case, manufacturers will tack extra digits onto the front or back, for purposes of their own. Generally speaking, using the three key digits, those will cross reference to a 6200 or 6300 series bearing.

In a nutshell the basic bearing number standard used today works like this. Standard bearings are 6xxx series. 6000's are light, 6200 are medium and 6300 are heavy bearings. Same thing for the 7xxx series, only those are angular contact.

Your 77206 is not a true angular contact bearing but it is listed as having the highest axial loading for a standard bearing. It should also have two shields. I suspect it is used here for thrust control.

Bearings run at high speeds usually specify shields not seals. I think the rpm limit for sealed bearings in the size you are using is around 9000 so no worries but still I think I might use shielded bearings instead of sealed. I think you will be fine with a 6305 and a 6206. Not sure what to do about the oddball, though. I think I would check to see why it is extra wide, maybe it's a double row. If so I would replace it with the closest thing I could find in the modern bearing catalog.

For most of my projects I buy my bearings from vxb.com. They're not perfect (who is) but they are very good and if something does go wrong they bend over backward to please the customer. And they ship FAST. Their VXB-brand bearings are not the best made but they are fine for non-demanding applications like we are discussing here. I've never had one go bad yet. And the prices are RIGHT. Check 'em out.
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