fitting bearings to a shaft advice

**Neale** · 28-11-2018

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** · 28-11-2018

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** · 28-11-2018

Originally Posted by spluppit

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** · 28-11-2018

Originally Posted by 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,

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