Shafts and Couplings - Which has a standard dimension ? 1

[edison123]

I have a broken motor shaft to be replaced with a new one but the motor coupling, which is also damaged, has not been sent to my shop.

Which part has the standard diameter for the interference fit?

1. Shaft dia - 125.00 mm and Coupling dia < 125.00 mm

or

2. Coupling dia = 125.00 mm and Shaft dia > 125.00 mm.

Any links to standards will also be appreciated.

 

[nickelkid]

Note sure what type(or size) of motor you have.

Standard NEMA dimensions:

http://www.electricmotorwarehouse.com/aosmith/page159.pdf

 

[edison123]

Thanks RCHandy. This is a German make. I know bearings have a standard bore and the shaft has the interference. I was wondering if it applies to the couplings also.

 

[nickelkid]

Most likely it is to the IEC standard:

http://www.usmotors.com/FL600/IEC-Dimensions.pdf

The SI tolerance will provide the interfernce between the shaft and bore.

 

[edison123]

Thanks RCHandy.

And idea where I can look up those tolerances ?

 

[nickelkid]

You need to now your shaft size and the IEC dimensions will give a tolernce spec, for example "J6"

The shaft and bore tolerances for J6 can be found in Machinery's Handbook

 

[Artisi]

Seems logical that the motor shaft would have the standardised dimension across all manufacturers with couplings bored to suit the motor shaft.

 

[juergenwt]

Most likely it will be an H on h fit (best fit you can get).
Shaft 125.000 h6 = 125.000 +0.000 -0.025
Coupling 125.000 H7 = 125.000 -0.000 +0.040

http://www.roymech.co.uk/Useful_Tables/ISO_Tolerances/ISO_LIMITS.htm

Scroll down to the bottom on left side and clk on ISO holes or ISO shafts.

Here is another useful site:

http://www.mitcalc.com/doc/tolerances/help/en/tolerancestxt.htm

Juergen

 

[juergenwt]

Sorry about my first post. The tables in the links are OK.
- I did some more research . The interference fit for cylindrical shaft ends is found under DIN 42946 as follows:

Shaft 125.000 m6 = +15/+40 (+0.015 to +0.040)

The coupling should be H7 = 125.000 0 to +40 (0.040)