Key stock fitting tolerance

[TheBrick]

Hopefully a easy one. I have a pulley that is missing it's key stock. What's the tolerance on ordering it? Measured with Verniers it's 7.9mmx7.5mm ->0.311"x0.295" ~ 5/16x9/32

7mm seems like it would be too loose but 8mm will not fit.

 

[Agroshield]

What is the shaft diameter that it is going on? What is the bore of the pulley?

It would be slightly unusual to use an imperial key with a metric shaft or the other way around.

The difference between 8mm and 5/16" is 2 1/2 thou. A practical solution is to buy 8mm and sand it down a bit for the proper fit (because you cannot 'sand it up a bit' on 5/16" if it is loose).

 

[TheBrick]

Thanks for the help as always.

Shaft is 38.1 - 38.14mm (multiple measurements) -> which converts nicely to 1.5". It's an old 13" South bend lathe so imperial from what I have seen so far on it.

I like the practical solution. I did wonder but I am always worried if my ideas are "bad practice".

The imperial measurement was me just converting metric to imperial then multiplying answer by 32 (or sometimes 64) and rounding to closest 32" to see if it could be anything imperial. I don't know if that's how it done in a professional setting but that's my method of conversation/ comparison.

 

[Erie Fred]

Any time I have had to replace a key, I always had to file them.
IIRC the keystock is made slightly oversize for just this reason.

Not something I like to do mind you.

 

[Barking Mat]

Any time I have had to replace a key, I always had to file them.
IIRC the keystock is made slightly oversize for just this reason.

Not something I like to do mind you.

What he said.

 

[Brad93]

Many keys will need hand fitting anyway.

Draw filing and finishing on a stone or emery paper on a surface plate.

 

[TheBrick]

Ah ok thanks for those additional pointers. Very interesting.