Looking for a reduced height square key for Nema motors

slnielsen · Sep 20, 2017

Hi.

I am in the need for a source for keys for Nema motors, but with reduced height.

We mount a coupling without a keyway on Nema motors, and to reduce unbalance we mount a key on the motor with reduced height.
Is that a standard part, that can be bought "off the shelf" somewhere?

Thank for any leads.

Br
Søren

slnielsen · Sep 20, 2017

Thanks Forrest, but maybe you answered the wrong thread?

Forrest Addy · Sep 20, 2017

Yes, I did.

AlexO · Sep 20, 2017

Mill down the usual key steel.

metalmagpie · Sep 20, 2017

So what holds on the keyless coupling?

metalmagpie

extropic · Sep 20, 2017

Never seen such a thing.

Can't you find a coupling with a keyway?

By the way, there are many, many types/sizes of NEMA motors so we have no idea what motor you're talking about.

Specify shaft diameter, key width and height to tangent.

slnielsen · Sep 20, 2017

Yes, that's the obvious solution. I know.
But this is to be used in a big company, and the circus involved of controlling a process like is humongous.
Therefor a bought, standard part, would much be preferred.

It's a coupling tightened on the outside, clamped together in two pieces around the motor shaft.
Size is from 15HP and upwards to 300HP
Attached is a picture of a 75Kw and upwards to 200Kw key we use on the IEC motors.

Tedger · Sep 20, 2017

Try GL Huyett. They can get you about every type of key made.

Bobw · Sep 20, 2017

If you just want half size height keys, that's easy.. McMaster Carr has the stock.

Thing is if you are looking for a half height 1/4" key, you probably aren't going to
find it.. You need to look for an 1/8" key that is a 1/4" tall and lay it on its side.

Might get lucky and buy some bar stock for about 1/5th the price that would be in tolerance..

HuFlungDung · Sep 20, 2017

I doubt that a half height rectangular key would fit above a full round shaft, inside a standard keyway in a coupling. The half height requirement begins from the (non) existent flat on the shaft.

steve-l · Sep 20, 2017

HFD,
You got it ass backwards. The keyway is in the motor shaft and the coupling has no keyway.

gbent · Sep 20, 2017

Is your balance so critical an unfilled keyseat is significant? If so, perhaps special balance motors should be purchased, specified with no keyseat. Or is someone in your company just being pedantic? What will you do with the portion of the keyseat that isn't within the hub?

slnielsen · Sep 20, 2017

Balance is pretty critical but OTOH the being pedantic is also possible. [emoji16]

Running at 3600 RPM this kind of missing mass can create some vibrations. But yes, is sort of a half-a$$ solution. But a low key, still will be better than none.

Sendt fra min SM-J510FN med Tapatalk

Limy Sami · Sep 20, 2017

Anything here ? 12" Rectangular Gold Plated Metric Keystock - Precision Brand Products, Inc.

or here ? 1 Meter Rectangular Plain Metric Keystock - Precision Brand Products, Inc.

Spyderedge · Sep 20, 2017

May I ask what kind if machine this is for? I have a very hard time visualizing a machine that requires up to 300 hp but is so sensitive that a few ounces on the motor shaft makes a lot of difference.

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Bobw · Sep 20, 2017

Since all we are trying to do is balance, how about a heavy metal/epoxy mix that approximates
the weight of steel? 1/3 tungsten (smashed inserts and endmills) and 2/3 epoxy should be pretty close.

OR lead fill the keyway, but cut it with aluminum chips or sand or something to bring the density
back to that of steel. You could even mold them up ahead of time.

Or how about cutting a second keyway or drilling some holes on the opposite side of the shaft..

............

You do realize that by making these things last longer, you are going to put yourself out of a job.

slnielsen · Sep 20, 2017

The part is for a centrifugal pump, with a seal cartridge close by.
Epoxy or lead or other chemistry is not accepted, I don't even have to ask.

Buying a motor with no keyway equals special orders aka longer lead time.
Tried looking at McMaster but with no luck, the keys were easy to find, but I didn't find any reduced?

Thanks for the help everyone, I'll keep looking. :cheers:

AlfaGTA · Sep 21, 2017

Drill a balance hole in the coupling on its OD and position opposite the keyway...Easy to calculate the amount of material to be removed based on the key way volume...
But in reality think you would be hard pressed to see any vibration from the out of balance based on the material removed on that shaft key way.....
Balance is all about distance from the rotational centerline.....in your case not much distance so the weight is not significant...also 3600 RPM is not fast...Now if we were talking about 20,000 RPM i might be worried.
Cheers Ross

Bobw · Sep 21, 2017

AlfaGTA said:
Drill a balance hole in the coupling on its OD and position opposite the keyway...Easy to calculate the amount of material to be removed based on the key way volume...

Or just broach the coupling and stuff a key in there.

Scottl · Sep 21, 2017

IMO you are more likely to find appropriate size rectangular steel that can be cut to length than a "shaft filler" size key. I would start by determining those dimensions and then look for appropriate stock.

AFAIK there are no rectangular keys that are 50% as wide as they are tall. Most seem to be roughly 60 to 75 percent, depending on size.

Looking for a reduced height square key for Nema motors

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