The Home Machinist!

What type of steel do I need to use for the steam dome cap? My boiler did not come one and I bought the locomotive from the third owner of this engine. What I have been told is that the boiler was built by Colorado Boiler Company. By the way the locomotive is 2.5 inch scale 2-8-0.

Andrew

Are you referring to the “pressure” part of the dome, or the decorative shell covering the sides and top?

Yes, the pressure plate.

Andrew

Drawing or photo of what it looks like?
And of what it mates to?
RussN

Here are some of the drawings of what it looks like and attaches to.
Here is what it looks like a top view of it and placement of holes.
What it attaches to on the boiler.
The red arrow is what I am talking about in this drawing.

I do know that it needs to be 4-1/2 inch round and 3/8 inch thick. This is also where you put the safety's and the whistle on.

Andrew

A36 to be technically correct.

I would be more concerned about the specs of the hardware holding it in place.

Actually that part is considered part of the pressure vessel and should be SA-515-70. A36 is a mild steel and is used for stay bolts.
These are per the ASME code. Even if you are not building a code boiler why not use code material.

John B

Following up on Bill Shields hardware concern and note on the drawing that calls out a "stud", the stud should be per ASTM A193 Gr B7 and the nut should be ASTM A194 Gr 2H.
Frank

I am a bit skeptical about a 'code' boiler design concern where they have you drilling and tapping into and past the welded joint for the steam dome...think about it.

It is probably OK..but...I would do it another way...unless the threaded holes are already there.