Fasten boiler and smoke box

[westy462]

How to Mate Boiler (3/8" wall) and smoke box (1/4" wall). Both 10 3/4" O.D.

[Builder01]

Make a a stepped ring to fit both inside diameters. Pick what ever wall thickness you feel comfortable for the thin part of the ring. Is the front tube sheet of the boiler even with the boiler barrel, or, a little distance from the end? If you have the front tube sheet positioned even with the end of the barrel end, this will be more difficult to attach.

David

[Fender]

This is from an earlier thread on this same subject:

"Marty Knox had a great idea for attaching a separate smokebox to the boiler. You machine matching 45 degree bevels on the rear of the smokebox and on the front end of the boiler barrel. Then, weld four square nuts set on edge into the inside of the boiler barrel and in a corresponding place on the rear of the smokebox. The nuts on the smokebox are drilled out to clearance size for the bolts that will hold everything together. When the bolts are tightened, pulling the nuts together, the bevels keep everything aligned. A small amount of high-temperature sealant between the bevels will form a good seal.
You may have to use socket-head cap screws (which have smaller heads than hex bolts). Goop up the threads with a generous amount of anti-seize."

[Marty_Knox]

We have found we need to use six nuts for 10" pipe. Here is a 6" pipe shell and smokebox

[blff cty lcmtv wrks]

i have built several of the allen moguls and ten wheelers, and the way i fasten the boiler to the smoke box is to turn down the o.d. of the smoke box end of the boiler to about half thickness. this is the part that sticks out past the front tube sheet and is not subject to pressure. i turn down for about 3/4 inch. then i take the smoke box and bore it out so that it slides onto the boiler. when i mount the boiler to the frame, i fasten it rigidly at the back of the boiler and leave the smoke box end a sliding fit. i will bottom the boiler out on the joint and then i pull the boiler back about .125 inch, so that when the boiler heats up and expands, it will slide up into the smoke box. at least that's how it's supposed to work, in theory. tell the truth, i have never ever looked to see if the gap ever closes up. it all covered up with jacketing. nobody has ever complained.

[Fender]

Guess I got the part about the square nuts wrong, because those are hex coupling nuts that Marty shows.