Greetings Gary, from a dull Norfolk.

You should never drill the shell of a copper boiler, unless it has been thickened with a pad or a bush used so that fittings can be screwed into a solid material.  Bushes are best made of bronze of some type.

Have a word with your local club’s Boiler Inspector.

Regards

Brian B

There are plenty of examples where copper boilers have been drilled for small fasteners directly into the boiler plates. These include such things as expansion angles fitted to the firebox wrapper, firehole door fixings and the like. Lots of boiler designs (a recently-looked-at example I came across is Martin Evans’ Columbia) call for tapping the boiler direct; the screws are always specified as bronze, as Brian says. Do not use stainless or brass, especially under the water level!

It would be ideal to have bushes for every screw, but on a finished boiler you have no real alternative other than tapping direct. Provided the thread diameter is not large in relation to the material thickness of the boiler, and you’re not drilling loads of holes near to one another, it should not affect the strength of the boiler at all. Caulking the threads with something like Loctite 542 should provide a perfect seal.

Threaded stays used to be commonplace, and you don’t fit bushes to every stay, do you?

However, it’s up to your Boiler Inspector to have the final say.

If you have a recognised boiler design any necessary plates will have been added during the boiler build, they will be shown on the drawings.

The Australian code AMBSC Part 1 for copper boilers, paragraph 3.13.4 states that:  Brackets may be bolted to tubeplates with bolts or studs having a length of thread engagement of not less than the major diameter of the threads. Where the plate thicknesses are insufficient to provide this length of engagement, a thickening pad shall be silver brazed to the inside or outside.

Best if possible is to check with a boiler inspector first, otherwise you may not be able to have the boiler certified and it will not be able to be operated at club events.