Tolerance

May I wish everyone on the forum who has helped me a peaceful 2022, but above all, good health.

A simple question, I hope! I need to fit two bronze bushes to a road spring eyes. I'm not sure whether we will be talking 'press' or 'force' fitting, but I don't think ther terminology is vital (forgive me). I'll be drawing the bushes in with a nut, washers and through bolt.

What I really need to know is the over-size for the bushes and, if possible, the formula. The eyes are 14mm ID plus or minus about 0.4 mm. I do have Machinery's Handbook but find interpreting it a bit difficult.

Many thanks in advance and, once again seasonal good wishes to all.

Martyn

all depends if the spring eyes are open or shut......

I would guess they are the open sort.....I would say .25 -.5 of a mill would be enough..per inch of diam.....

subject to wall thickness.....

if the wall is thin it will alter the size of the hole......

most spring bushes of modern decent were made so that once pressed in they ended up the correct ID size.....

In the old days they were roughed out and reamed once fitted....

also be careful that the eye is prop round.....if the tail of the spring is not prop formed it can distort the bush....

look at the old bushing for extra marks where the spring eye ends....often a big gouge mark....

For folk like us a sliding fit and high strength loctite is much easier. Odds are it will be stronger too as the hoop strength of a small, pretty thin wall, bush isn't that great. Hence the bush will tend to compress running away from the fit load reducing the grip between bush and eye. Maybe compressing enough to necessitate reaming to restore the size.

Force fitting with a nut, washers and through bolt can be a little fraught too. So easy to pull the bush in a little tilted.

Oilite bushes are diffrent. The specification gives you a hole size ensuring the bush is both tightly gripped and reduced to its nominal bore size. My experience is that oilite are much easier to draw in straight than shop made bronze.

Clive

Edited By Clive Foster on 01/01/2022 15:38:00

Most are happy with the terms press fit, force fit etc and Loctite.

However fits and tolerances are clearly defined and charted:

The above takes quite some working out but should be useful once it is understood.

Try to make the hole first. The reamer, if not home made should have the size marked on it. Just as important is the limit and fit, usually H7.

An example: You want a bush with a sliding fit on a 25,00mm shaft. You ream the bore using an H7 reamer. This should give you a bore between 25,00mm and 25,02mm. The required limit and fit on the shaft would be g6. This gives a shaft diameter between 24,98mm and 24,99mm. The number 6 suggest that you should be able to achieve this by turning or grinding. You need good measuring instruments for this and experience.

Back to the Loctite!

JA

I agree with Clive, Loctite and a sliding fit will cause no distortion and be easy to assemble.

14mm Martyn? - Lord Austin would turn in his grave if he heard you saying that !

I think you will find that the spring eyes are not truly round and that you should ream the bushes after pressing into place.

Ps How did the radiator cap go ?

Bob

What vehicle ? more to the point what is the OD ? If it's a normal road spring then the eye will open up to hold the bush ! I would ream after fitting ! Good luck Noel.

If they are to be fitted to the end of a leaf spring, you are not fitting inside a tube, but in a open ended spring which can stretch. That means that the interference can be much greater, but the bush would need a chamfer. At least 0.080" or 2mm would probably work. Rubber bushes are used in more up to date vehicles.

Forty years ago, before the general use of rubber bushes for road spring eyes for H,G,V,'s, replacement bushes for A.E.C,, Leyland, Ford et.al were obtained as spare parts. When I was on the shop floor, we normally removed the roadspring from the axle, pressed the old, worn bush out on a hydraulic press, used the press to install the new bushes, and always had to ream the bush to fit the shackle pin with an adjustable reamer. On some vehicles, thrust washers on each side of the eyes had to be renewed also. By coincidence, only yesterday I was boring out some washers for a little job in hand, they were originally made for Bristol bus springs, 1" bore, 1 7/8" outer dia., 5/32" thick. Both faces ground and beautifully made, as were most parts from the Bristol Motor Co. These washers are at least 40 years old.