pin size

[motorworks]

Hi
I just stub a shaft in an electric motor(old shaft was bent), and I was wondering what size cross pin I should use.
The stub is 60mm in diameter and it goes into a shaft that has been bored out for a slide fit on the 60mm stud and the OD of the female end is 78.5mm.The lenght of engagement is 63.5mm
The electric motor is 35hp.
thanks
eddie

http://www.geocities.com/motorworksnf/123

 

[israelkk]

First of all, what are the materials, the heat treatment and tensile strength of the motor shaft, the "stub" and the pin?

What is the maximum torque that can apply on the motor shaft?

Knowing these values then basic double shear analysis on the pin can give the desired pin diameter and if it possible at all.

From the fact that the shaft was bent I assume that there is a bending moment too. This will complicate the pin calculations a little bit more.

 

[motorworks]

"the heat treatment and tensile strength of the motor shaft, the "stub""

Not sure on the motor shaft, but it machined like C1020.
I made the stub from 4140 HTSR

"What is the maximum torque that can apply on the motor shaft?"

Not known, just that it is 35 hp.Job from a local rewind shop.
The motor shaft got bent when it was dropped!!
Hope this helps.

http://www.geocities.com/motorworksnf/123

 

[Barry1961]

I would use some type of shaft locking or press fit compound. Loctite is one brand and has a product called "press fit repair". Degrease both parts well.

If you want to also use a pin I would use one 10mm or less due to the wall thickness.

Barry1961

 

[jet1749]

The motor full load braking torque is T = 5252 x HP/rpm. So 105lbft for 1750rpm and 52lbft for 3500rpm. Why not shrink fit the stub onto the motor shaft. I can't see that a cross pin will provide an adequate drive arrangement on a slip fit stubshaft
regards
John

 

[Barry1961]

The people in the electric motor forum might have some good ideas. I have seen a few threads in there about replacing motor shafts. I think the common way is to press old shaft out of rotor and press new one back in.

There may be some issues with eddy currents with a stub shaft.

Barry1961

 

[desertfox]

Hi motorworks

Before you pin, shrinkfit or bond your shaft to the motor you need to know the maximum torque the motor can deliver.
Only then can you decide pin size etc based on the material
you intend to use. (echoing israelkk sentiments)

regards

Desertfox

 

[Tmoose]

The motor shaft diameter and DE bearing is based on handling radial loads from belt drives. Any inserted stub will be pretty weak in bending compared to a one-piece shaft. Loctite or none, It will try to wobble like Triumph's cigar, 1800 times/minute

http://la.indymedia.org/uploads/2005/03/stuffed_dog_w-cigar.jpg

 

[zekeman]

If you dropped that motor, chances are that the shaft is bent right upto the press fit end of the motor. Best bet is to replace the hole shaft, since as others have mentioned you will always have concentricity and strength issues.
If you don't have the facility for doing this, give it out to any reputable machine shop.