fitting bearings to a shaft advice

[Clive S]

Hi,

I'm making up a rotary indexer. In the headstock build i'm using a ER32 collet shaft extender. The shaft is 32mm OD and bearings 32mm ID but they are too tight a fit at the moment to slip on.

The difference as measured by a collegue (shouted across the room) is 5000th of an inch, or 0.0127mm in my world.

Will heating the bearings allow me to get these on or should I be looking at getting the shaft turned down, or another method?

Thanks

Try putting the shaft in the freezer overnight But have you got an extra zero in there

[marbles]

Try putting the shaft in the freezer overnight But have you got an extra zero in there

Thanks, will do.
Highly likely I have an extra zero 😀

[Neale]

Just done some quick sums based on rough coefficient of expansion of steel. If your diameter difference is correct, then you will need a temperature difference of around 55C to get enough expansion/shrinkage. So, bearing in oven to, say, 100C, and shaft in freezer to give you around -15C. Difference should then mean that the bearing will drop on with a very small amount to spare, but will grab quickly as the temperatures equalise.

Saying "5000th of an inch" is a bit difficult to interpret. I think you actually mean "half a thousandth of an inch" or "half a thou" or 0.0005", which is the imperial equivalent of 0,0127mm. Shows one advantage of the metric system!

Good luck,

[spluppit]

I misread the original post and as Neal said expressing it as 5000 of an inch is misleading. That interference is fine if it's measured correctly. It needs to be pressed on squarely using tallow. Pressing things square here is the key. Put a shoulder on the end of the shaft if possible that is a slide fit on the bearing then press. This will keep the bearing square. Also use tallow if you have any.

[marbles]

Put a shoulder on the end of the shaft if possible that is a slide fit on the bearing then press. This will keep the bearing square. Also use tallow if you have any.

Thanks for the advice. I'm a tad light on tallow, never had a calling for it, must be something else I could try as a sub. I'll try the freeze and shrink thing first and see how that works.

[marbles]

Just done some quick sums based on rough coefficient of expansion of steel. If your diameter difference is correct, then you will need a temperature difference of around 55C to get enough expansion/shrinkage. So, bearing in oven to, say, 100C, and shaft in freezer to give you around -15C. Difference should then mean that the bearing will drop on with a very small amount to spare, but will grab quickly as the temperatures equalise.

Saying "5000th of an inch" is a bit difficult to interpret. I think you actually mean "half a thousandth of an inch" or "half a thou" or 0.0005", which is the imperial equivalent of 0,0127mm. Shows one advantage of the metric system!

Good luck,

Yeh I think your right about the "half a thousandth of an inch" or "half a thou" or 0.0005" :)