Press fit sizing

Hello, I know that the mantra for a press fit is 1 thou under size per inch. However I need to fit an Oilite bush (18mm OD and wall thickness 2mm) into an aluminium casting.

I don't normally work with this material combination and I would suggest that the 1 thou under size per inch rule may not apply here. The casting is only 3mm thick in places around the bore, so it might be easy to crack if too tight a fit. I am almost tempted to loctite the bush in place, as being less risky and less in the way of accurate reaming required.

Your thoughts?

Andrew.

Oilite bushes from memory have an oversize bore which closes down to the correct size when pushed into the correct size housing, there are sites which give you the reqd data, also Loctite will not work on oil impregnated bushes [I think?]

Tony

I've had success in the past with making it a "tight" fit rather than the tighter "press" fit & then using Delta Bearing Grade liquid number 22 to stick it in place, hasn't failed me yet in fairness, although i did also have reservations about the oil impregnation of the material i was sticking just like you Mr Pratt. you could always do a test piece maybe ?

Best to buy a recognised brand oilite type bush rather than a generic and follow the instructions in the technical data.

Must be over 20 years since I last used any but, as I recall it, the bush was slightly oversize relative to its nominal OD so that when pushed into the nominal OD size hole the necessary contraction would occur to create a correct size bore.

If my memory is correct that seems a very logical way of going about things. Presumably the installed bore tolerance would follow hole tolerance too.

Clive

I don't recall Luas dynamo rear bearings being any more than a firm ball of the thumb push, though 1970 was a while ago.

The drawing should specify the correct hole 

Edited By Dave Halford on 24/04/2021 21:02:04

Oilite bushes are designed to fit a H7 tolerance reamed hole. There are various standards available but the H7 is the most common.

Phil

Thanks everyone, I shall try for an H7 fit and if I fail then loctite is my friend. I have never had a problem with loctite and oilite bushes, despite the oil impregnation, it still sticks.

Andrew.

Edited By Andrew Tinsley on 25/04/2021 11:13:12

I’m with Phil P , oilite bushes go into standard sized reamed holes.

Edited By bernard towers on 25/04/2021 12:31:48

In the UK we generally work on the Hole Based System of tolerances. Capital H being the designation, these holes are always plus on the Nominal Dimension. All limits and fits are therefore applied to the Shaft or Bush being inserted and are lower case letters.

The Zeus handbook gives all the relevant details of the most commonly, or Preferred Limits used.

The Oilite bush will therefore come above the nominal size, to fit a standard H7 Hole. That hole being, as a Very Rough rule of Thumb, plus 0.025 mm or 0.001", a Smaller hole is less than, while a Larger hole more than.

A certain amount of deformation of the Oilite bush occurs during insertion and the bore of the bush should be a Standard H7 hole after insertion.

On the Continent they prefer to work to the Shaft Based System, the shaft designation carrying the Upper case letter, and all holes, Lower case, these holes are machined accordingly.

Hope these notes help,

Regards

Gray,

Edited By Graham Meek on 25/04/2021 13:00:36

Thanks again everyone,

I managed to ream a correct size hole and pressed in the bush and all is now working as it should, Still have a problem using adjustable reamers, even good (Presto) ones. It is a bit of a lottery on final hole size. But I did creep up on it with multiple passes.

Andrew.