Replacement of boiler side stays

[samesgonzo1]

The boiler in question is an LMS 8f in 3 1/2" gauge (Not to Martin Evans Euston design) The construction is copper plates and silver solder through out, No soft solder. The side stays of the firebox are 1/8" copper rivets with the heads on the inside of the firebox and silver soldered in place (not screwed and nutted) The boiler is approximately 40 years old and has been steamed almost every week.
The Problem: A row of stays approx. level with the firehole door have the heads erroded  and some of the stays are now leaking. This bolier passed the hydraulic and steam tests at the appropriate time.
The required solution is to remove all rivet stays that are suspect and replace.

Please can the experience boiler makers / repairs in this group suggest a method to remove the existing stays and have you suscessfully used this method yourself or know of its use. 

I do not think simply drilling them out from the outside and expecting the drill to  follow the rivet shank and enter the inner firebox plates has any prospect of working.

I have considered the possibility of making a thin wall tubular cutter with a bore  just over 1/8" so that it will follow the rivet shank stay and thus maintain alignment with the existing holes. An oversize stay could then be fitted.

I have access to a bridgeport vertical mill so could possibly use a slot drill type cutter.  The the problem is setting up so the cutter follows exactly the existing stay rivet. Given this is a copper boiler it cannot be certain the existing stays are exactly perpendicular to the firebox outer wrapper.

Proven methods preffered but any sensible suggestions considered. 

Thanks for your ideas

[kelvin]

Firstly my comment is that if you've had forty years of weekly steaming from this boiler then it doesn't owe you anything! The chances of a successful repair are very slim, even if you can can remove the side stays attempting to silver solder replacements into place will set off further leaks and you will have wasted a lot of time, gas, copper and silver solder. Using the method you have described to remove the old stays would be an interesting exercise. I have never heard of it being done. At the moment the boiler is scrap so you have nothing to lose. If you were successful then oversize ( and these would be well oversize) screwed and nutted stays could be fitted and there's nothing to stop these being caulked with soft solder. Although this method has been denigrated and even said to be " against the regulations" it was made clear at a Federation seminar a couple of years ago that this is not the case. However, you would have to obtain the agreement of your club boiler inspector.

I had a similar problem but decided to scrap the boiler as a replacement became available at a very competitive price. Boiler making with new materials is fraught enough, repairs to an old boiler , particularly the inner firebox, are in the lap of the gods. Anyway, good luck with your chosen course of action.