Brake calipers.

a

a solid

don't

At a very basic level you are correct, but there is still no legitimate comparison between the two types. I'm surprised you don't understand that.

An engine piston has to cope with a high linear speed, pressure. Including side thrust and heat.

A brake piston doesn't have to contend with any of the above. Basically, as long as it mates with the bore seal, with no leaks, and is strong enough not to collapse under braking pressure, it'll do the job. Mike.

Reply to
Mike G
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No, each bit met its tolerances just fine, and any one might have been fine matched with other productions (which is what we did, by the way).

You claimed (above) that

"As long as a component conforms to the drg tolerance, it will fit a mating part made anywhere else that also conforms."

which is simply not true if the parts made in different places then have to be matched in pairs. You can't put instructions on a drawing relating to an unknown part made elsewhere.

Again, that's just plain wrong. Sorry.

Ian

PS I do realise that you said "mating part" but am ignoring that this means you claimed that parts which fit together will fit together!

Reply to
Ian Johnston

Sorry to be so late in commenting, but I'm having problems with my news feed.

This is the case with engine pistons as the skirts make some contact with the bore - and they may well have been selectively assembled at the factory anyway.

However, I'd happily use the 'wrong' piston in a bore provided it was of the correct size and was fitted with new rings - and have done just this on Mini engines.

But a brake caliper piston doesn't - or shouldn't - touch the bore - that's the job of the seals.

Reply to
Dave Plowman

component

tubing

bit

that

Tolerance.... Meaning the permitted variation in certain characteristics of, in engineering, a workpiece.

Your mistake is in thinking tolerances always refer to simple plus minus sizes. They don't. Could refer to material, hardness, or qualified by notes, whatever.

"and each size must fit into the one above" Which they didn't. And you say that's within tolerance. Notes like that have to be read as a part of the tolerance. You can't just ignore it and say the parts were still within tolerance.

The tubes didn't fit because they didn't conform to the stated tolerance. Period.

fit a

then

drawing

It's usual and preferable, for assemblies containing matched parts, to made by the same Co, but there's no reason why a Co can't be supplied with components made elsewhere, that the parts they make must match up with. In which case there'd be a note, or 'instruction' on the drg to that effect.

In any case we are not talking about matched components. It's about caliper pistons and their bores.The wide clearance between a caliper piston and it's bore makes matching unnecessary.

You should be. Don't be so patronising. You obviously don't understand that a good drg can cover all eventualities. To the point where if things don't fit together, it's because a part or parts don't conform to the drg. IOW a manufacturing error. Mike.

Reply to
Mike G

You reall need to think about this a little more carefully. When parts have to be matched it is, by definition, because not all possible pairs will work together.

It's not that tricky, really.

Ian

Reply to
Ian Johnston

together,

When parts

possible

You are wrong. Obviously you are refering to what is known as selective matching. where the individual parts are mass produced, then selectively assembled, or matched, but.that is only one of the ways that matching is achieved.

The manufacture of precision roller/ball bearings etc, is a classic example of selective matching. Used to achieve the accuracy needed.

But it can also be a part of the manufacting process. where parts are matched as they are made. A part being made, with the matching part being machined to fit.

An example is that of bushes that need to be a good fit on a shaft. A common method is to make them slightly u/s then hone them to fit a mass produced shaft. They become a matched pair, but no selection is involved.

Apparently it is, as you still don't understand how a drg should cover all possibilities for errors in manufacture. That being one sign of a good drg.

You persist in arguing about matched components, in your attempts to prove me wrong, but you really need to have a better understanding of engineering and manufacturing processes, before making statements that are so easily shown to be wrong. Mike.

Reply to
Mike G

The message from "Mike G" contains these words:

ISTM that an essential part of matched parts is the selection. IMO the process described in the paragraph immediately above is not at all about selection. It is the old fashioned method of make (or finish) to suit. In the sense used the part would still be a matching part even if it didn't actually fit.

Roger

Reply to
Roger Chapman

Oh, so you think that the designers who specify matched components are wasting their time, do you?

You need to discover the difference between a manugfacturing drawing and an assembly drawing ...

With all due respect, son, you'd be better to try this argument after you've produced, or at least seen, some real engineering drawings.

Regards,

Ian

Reply to
Ian Johnston

better

before

argument after

drawings.

You have no idea of my age or my engineering experience. Having worked in many branches of precision engineering all my workig life, including design, your patronising assumptions have as much basis in fact as your argument. I suggest you take your own advice. In any case I have no interest whatsoever in continuing what has become a futile arguement. You're obviously not open to any views bar your own. You can conclude what you wish from my decision. Mike.

Reply to
Mike G

the

the

IMO the

all about

to suit.

if it

I understand what you say, but selection is not an essential of matching. Matched parts simply means that 2 or more parts in an assembly are matched for a specific fit or clearance. Achieving that is not necessarily just by by selection. Parts may be made to fit. The economics of the production process, would dictate which method was used. Smaller production runs are more likely to have their parts made to match, whereas selection could be the better method for higher volume production. Mike.

Reply to
Mike G

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