Electric motor balance, Special on my Lodge & shipley

The 15 HP General Electric motor on my Lodge & Shipley lathe has a note on the motor plate. It says "special balance .00075". Anybody able to shed some light on this?

moonlight machine said:

The 15 HP General Electric motor on my Lodge & Shipley lathe has a note on the motor plate. It says "special balance .00075". Anybody able to shed some light on this?

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A COMMON marking on a GE KinaMatic is "SPECIAL MACHINE TOOL DUTY". That was their (feeble) attempt to match a Reliance "Type T".

I am aware of specially balanced motors, but not familiar with the way they are spec'ed. This figure "looks like" TIR. The thing to preserve might be a higher-precision of bearings than ordinary. Dirt accumulation can affect balance, of course.

Better than average balance is a plus, but you'd probably not miss it at the low RPM's these motors deliver.

GE (nor Louis-Allis) DC motors were not BAD DC motors. Just not Reliance DC motors!

Monarch Lathe will probably have the correct brushes, BTW. The 10EE ones I bought from them were made by Helwig Carbon, but made to an OEM part-number and specification one cannot even find on Helwig's menu. Monarch might have to buy them in batches, special order, and wait for them. I'd recommend Monarch for bearings for the motor, too, if they stock those.

IOW - best to buy from Monarch. There wasn't much mark-up, and they'll be the right parts for-sure, not just "maybe".

This is on a 220 / 440V 1725 RPM 3 ph AC motor.

moonlight machine said:

This is on a 220 / 440V 1725 RPM 3 ph AC motor.

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As said "low RPM".

Relative to where DC (or any other..) motor "usually" has to have special balancing, anyway. In your case, it is the size and mass. On any fairly large motor, read "heavy", any imbalance is not trivial.

Above 5K RPM. Think 10K, 20K RPM "HSM" CNC spindles.

Or even small goods. One could buy a used car for what Fischer Spindle wants to rebuild and re-balance a small, but 17K RPM "Precise" electrically powered jig grinder, f'rinstance. The rotating mass is many times as heavy as an air-powered grinder.

Anybody got anything on the topic?

moonlight machine said:

Anybody got anything on the topic?

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Balancing of motor armature and shaft is available as a service. Next bay over at Galis, our "motor shop", had the gear and skill. Now and then we'd turn armature shafts, (100 HP, 600 Volt Dee Cee) they'd vet our work. Check with the upper-tier rewinders near you.

If you think yours NEEDS re-done.

I'd wait and see if it vibrates, meself. It's a tad time-consuming to drag the booger in and out of its perch, let alone rig for DIY balancing.

Quick Google search comes up with a relevant page from the GE motors catalogue :- GE Standard Motors Product Catalog .

Summarising motors tested as per NEMA Standard MG-1 Part 7. Spiffy little tables giving permitted maximum vibration in inches/second, whatever that may be, or inches peak to peak. For twin ball bearing motors Special is 0.075 inches per second or better at all speeds. For one ball bearing and one roller it varies with speed but for the relevant 1000 to 1500 RPM range its 0.001 inches peak to peak i.e linear displacement at that frequency.

Simple specification hiding considerable complexity.

Clive

Imagine a 4 bar linkage suspending two vblocks. Give the rotor a spin on its bearings resting in the vblocks, if its unballanced the v blocks will swing back and forth. Test indicators on both side to measure the movement. The phase of the two indicators movement also needs to be measured.

This is just speculation though, but i would read that distance given to be the be the offset between the bearing to the center of rotation.

So you can calculate the acceleration at a given rpm, and multiply by the mass of the rotor to find the force on the bearings for a given rpm.

Normally, I usually see balance factors in grams, so I'm not sure what to make of your number. Maybe ask Frank or Tom over at Maritool. I know they balance their tool holders ( basically ) daily, so they may be able to shed more light or at least have relevant conjecture. I'm inclined to agree with Bill on this, though. Shoot for best as you can, and see what happens. It's not like that is actually "fast" or abusive.

moonlight machine said:

The 15 HP General Electric motor on my Lodge & Shipley lathe has a note on the motor plate. It says "special balance .00075". Anybody able to shed some light on this?

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This is a 50's or 60's Powerturn right? More than anything, I would guess the purpose of that little nameplate was to impress the end user.

Look at the sales literature and operation manuals for heavy machine tools from that era and it's clear they were all fighting to be the best of the best.

If you ever have to replace the motor bearings you will buy whatever bearings you deem appropriate or can afford. That probably won't be any kind of super precision stuff. Not sure that .00075 classifies as super precise either though.

Clive603 said:

Quick Google search comes up with a relevant page from the GE motors catalogue :- GE Standard Motors Product Catalog .

Summarising motors tested as per NEMA Standard MG-1 Part 7. Spiffy little tables giving permitted maximum vibration in inches/second, whatever that may be, or inches peak to peak. For twin ball bearing motors Special is 0.075 inches per second or better at all speeds. For one ball bearing and one roller it varies with speed but for the relevant 1000 to 1500 RPM range its 0.001 inches peak to peak i.e linear displacement at that frequency.

Simple specification hiding considerable complexity.

Clive

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A one-thou excursion is close enough to "never mind", and his one at: "special balance .00075" is hardly enough "better" to worry over.

The motor, here, is not the spindle itself, and even so, a(ny) lathe spindle MUST be able to deal with unbalanced work pieces.

I'd leave it be and move-on to "the next".. wotever needs TLC.

thermite said:

A one-thou excursion is close enough to "never mind", and his one at: "special balance .00075" is hardly enough "better" to worry over.

The motor, here, is not the spindle itself, and even so, a(ny) lathe spindle MUST be able to deal with unbalanced work pieces.

I'd leave it be and move-on to "the next".. wotever needs TLC.

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I don't even have power to it yet. I just have never seen it before and was curious.