Press fit bush

Hello All,

I need to make a bronze bush to fit into a cast iron tractor clutch pedal.

The clevis pin hole is well oval.

I have plunge milled the pedal out to 14mm and the clevis pin is 10mm.

With a 2mm wall on a bronze bush having an interference fit (pressed),

into cast iron, what outside diameter would be recommended for the bush?

I imagine a slight tad over 14, but how much would this slight tad be ?

Exactly ?

Thanks in advance for any help

.

I flatly refuse to discuss exact tads with a man who works in whole millimetres

... But you may find this useful:

http://www.tribology-abc.com/calculators/e3_8.htm

**LINK**

MichaelG.

Edited By Michael Gilligan on 13/09/2016 18:27:38

Loctite it to avoid tensile forces in the cast iron.

Martin

I would also check your hole as plunge milling may be spot on but more likely a tad under or a tad over 14mm.

For a practical idea I have just mic'd a sintered bronze bush and it is 0.003" oversize on 3/4" nominal size, not tapered. So thats a a tad over 0.075mm for the press if but if the iron is a bit thin you may want to try 0.04-0.05mm over bore dia

If feasible, ream the bush after fitting, if the fit is critical, (which I guess it isn't).

I support Martin, a 2 mm wall in cast iron will fracture without warning. Niko.

We don't know how thick the iron pedal is.

The hole in the pedal is now 14mm, the pin it pivots on is 10mm which gives the BUSh a 2mm wall thickness

Have a look at Oilite, Manganese Bronze. Although these are not re-machined after fitting, they achieve the correct bore after being press fitted into the correct hole.

Thank you for the link. That is a cool calculator.

The complete absence of any decimal points, let alone anything after them, was an effort to maintain the agricultural spirit of the adventure. However, even as I pressed the "create thread" button, I saw that this was doomed. At some point I would need to resort to something a bit smaller. It's a pity that the DRO doesn't do Tads, really.

Thank's everyone for the replies. Last night's forum time was cut short by a storm and power failure.

Martin - I had temporarily forgotten about Loctite; that is most likely the way to go.

Neil - I will ream the bush after fitting. Critical it isn't, by any stretch of the imagination, but seems good form.

Jason - The pedal is about 15mm thick. My tape measure is not equiped with smaller increments.

And, of course, for the loctite solution, the finished article only needs to be a Tad, or two, under 14mm.

No unnecessary stresses, etc, either on me, or the pedal, and not a decimal point in sight.

Daniel, if it's the clutch foot pedal I doubt it is cast iron, more likely a steel forging. What tractor is it ?

John

Edited By JohnF on 14/09/2016 08:31:12

PostScript: ... For the benefit of those who may not be familiar with the term:

A 'tad' [or more properly, T.A.D] is a Tiny Atypical Dimension

Example: On a drawing generally dimensioned in inches; one micron would be a 'tad'

or, when referencing whole millimetres; tenths of a thou would be 'tads'

MichaelG.

You're probably right, i can't imagine that being a casting either.

Michael W

[ BLUFF ]

From a practical point of view it would not matter if the bush was loose on the peddle hole by a couple of thou. It will not wear the peddle out in your lifetime and will be retained by the peddle fixing.

[ BLUFF ]

Micheal - That saved me the trouble of some research. I was convinced that a Tad was a more or less precise measurement. It's true that whole millimetres can be a bit (tad), cumbersome.

I've sometimes been known to use "half a Tad", but that is only on extremely precise work., and somewhat rare.

The (non) deliberate mitsake of referring to the clutch pedal as cast iron is just that; a mistake.

As pointed out, it is most likely a steel forging or similar.

The tractor is a Someca 40 & French.

Chris - quite agree with you, that the bush could even float. I just wanted to do a reasonable job for the simple pleasure of doing so; as with most of what we get up to. Avoiding any unnecessary accuracy, of course.

Sorry - can I change the thread title now ?

I'm thinking "Loosely Fitting Bush", may be more appropriate.

For the diehard Imperial brigade I'm considering making a Micrometer which reads in 1/1024" increments. That's 2 to the power 10, and is a logical extension of 1/8", 1/16" etc. Any takers?

Works even better if we redefine the inch to be 25.6mm as well.

Dave