rootboy 

Could be Ed. When I drilled one set out, it seemed the pins were seized within the upper and lower pivot body parts. It could have been a dissimilar metals corrosion issue. Not sure. But they were extremely tight. Almost felt "welded" together. I tried all manner of penetrant and blaster, etc. But I didn't try heat.

Ed.

Coefficients of Linear Thermal Expansion

If I had one busted I'd do some testing, but I don't...

rootboy 

I've sometimes been fascinated by this phenomena, Ed. I'm usually fascinated by things I don't understand.
For instance, if you heat, say, an upper pivot body of the derailleur in this thread, which has holes bored through it to accept the pins, do not the holes grow smaller as the material expands? It would seem so, to me. That the inside diameter of the hole would decrease as the material surrounding the hole, expands. And, that the pin would increase in diameter as its material expands with heat.
May be counter-intuitive.

Not to derail your thread, 1987. Which seems to be slowly moldering anyway.

repechage

If you heated things up and a bore shrank, then I would never have been able to replace the valve guides on my Corvair's cylinder heads. I heated the heads to as close to 500°F as possible and dry iced the guides. A long process as the head temp dropped off fast out of the oven.

gfk_velo

Just some general engineering notes, as we are not only the main Campagnolo SC for the UK but we also run a machine shop here & make all sorts of odds and ends - we are framebuilders, too ...

Heating looks like a good solution and contrary to the logic of the thing, what Ed says is correct - the bores will open up a tad under heat BUT ... I don't know and have no immediate way to find out ... Campag may have used some form of heat treatment on their alloy parts in this era. Certainly they do now. So, heating *may* not be a great plan - you might end up disturbing the strength characteristics of the alloy. We have seen cranks fail where they have been heated to removed seized pedals, for instance.

ID of the bushings - a taper gauge is the standard way of doing this - they can be made by turning a rod at a known taper angle from a known starting diameter - establishing the diameter at any given point is then simple geometry. The shallower the taper is made, the more accurate the measurement. Introduce the rod into the ID you are tying to measure, measure the amount of rode enclosed by the ID and do the trig & "voila"! The downside is that you can only measure the entry-hole size so if it's tapered, you then have to engage in a bit of rather tedious trial and error ... an alternative would be a digital photograph shot from a distance with a long macro lens to minimise spherical abberation, with a scale alongside, then to scale the image on screen. Not super-accurate though, unless you *really* know what you are doing ... we've used both of these methods at various times on pretty small stuff.

Pressing bushings that small - I'd make the bushing a couple of mm over-length & use a steel central guide that is a snug fit (maybe 0.05 or 0.1 mm dia less than the ID of the bushings) as a guide and a 2 mm "deep" cap-type drift on the guide to gently sqeeze the bushings in with a fine screw thread. Once the cap-type drifts come up against the alloy, so the bushings are all the way through the alloy, take the mini (micro?) press out & cut the ends off the bushings nearly flush and then use a properly ground, big drill to clean the driven and cut ends up. It's a faff but if you are determined ...

HTH
Graeme
Velotech Cycling Ltd
Campagnolo main SC, UK

shopco43

ID of the bushings - a taper gauge is the standard way of doing this - they can be made by turning a rod at a known taper angle from a known starting diameter - establishing the diameter at any given point is then simple geometry. The shallower the taper is made, the more accurate the measurement. Introduce the rod into the ID you are tying to measure, measure the amount of rode enclosed by the ID and do the trig & "voila"! The downside is that you can only measure the entry-hole size so if it's tapered, you then have to engage in a bit of rather tedious trial and error ... an alternative would be a digital photograph shot from a distance with a long macro lens to minimise spherical abberation, with a scale alongside, then to scale the image on screen. Not super-accurate though, unless you *really* know what you are doing ... we've used both of these methods at various times on pretty small stuff.

Here are three ways of measuring small holes. First, the way I generally use, is to use Gage Pins. These come in sets (8 of them) and range from 0.011” to 1” in 0.001” increments, the first set being from 0.011” to 0.250”. The sets can get expensive but the first one is the cheapest, especially if it is Chinese. Also you can buy individual pins so if you have a rough idea you can go that route. The second way is with Small Hole Gages. Starrett (and others) make several types of these but they are limited to a minimum of about 0.0120”. the third way that comes to mind is using a hand held Optical Comparator. This is a 10x loupe that has various scales, including circles and angles.

cs1

This is a great thread. Has anyone tried this on a Shimano derailleur? Shimano and later Campy have blind holes on one end.