This page describes fabricating the smoke box, throttle, superheater and steam plumbing to the cylinders.
Smoke Box Drilling: The smoke box is simply a 8.5" length of 8" OD 1/4" wall steel tube with lots of holes. The first thing I did was to mount the tube in the lathe and square up the ends. Next, about 0.01" was turned off the inside where it slips over the boiler tube to make it easier to slide the two pieces together.
The most difficult part of drilling the holes is to get them positioned accurately. The big hole for the smokestack was started with a 1" step drill and then finished with a boring head in the mill. The holes for the blast nozzle and the steam supply to the cylinders were made with a step drill.( Step drills are much easier to use than regular drills for large holes in relatively thin material and especially thin curved surfaces.)
The photo shows using a template to drill the rivet holes near the back of the tube. The template hole locations were center drilled in the 1/8" X 1/4" CFS bar on the mill using the digital indexing. The holes were then drilled through on the drill press. The bar was then heated and bend around the end of the boiler to get the curved shape. The template was clamped to the smokestack tube and the first hole drilled through the tube. The rivets will be #2 drive screws so # 3 screws will fit in the holes. After the first hole was drilled, a screw was inserted in the hole, nut attached and tightened. A hole is then drilled at the other end of the string of holes and a screw put through that hole. With both ends of the template secured with screws, the remaining holes in the template were drilled through. The template was removed and repositioned at the end of the first set of holes with a screw through the last hole in the template and through the end hole in the smoke box. The process was started at the top and holes drilled down both sides with the meeting point at the middle bottom where the different spacing between the last rivets won't be noticed.
Throttle: The photo above shows the throttle valve and associate plumbing. The throttle valve is located in the steam dome. The long pipe runs from the valve above the flues and through the front tube sheet into the smoke box. The valve, the street elbow and the short pipe out the top of the valve is inserted through the top of the steam dome. The long pipe is inserted through the front tube sheet and threaded into the street elbow. All these fittings are 3/8" brass pipe.
The right end of the long pipe has been modified. A short piece of 3/4" hex bar stock was turned to 3/4" diameter with about 1/2" of the hex left on the end. The center was drilled to 5/8". The OD of the end of the 3/8" pipe was turned down from about 0.675" to 5/8". This 3/4" OD piece with the hex end was then silver soldered onto the turned down end of the pipe. The 3/4" OD of the end fits into a 3/4" compression tube in the front tube sheet. The stop in the inside of the compression fitting was drilled out so that the 3/4" OD of the modified pipe will slide all the way through the fitting. The compression fitting seals the pipe. The 3/4" hex on the end is used to screw the pipe into the street elbow under the valve. The last modification to the end was to drill the end 1/2" (the 3/8" pipe has a ID slightly less than 1/2" ID) about 3/4" deep and to silver solder a piece of 1/2" OD tube into the end with about 1/2" extending beyond the hex piece. This 1/2" OD tube on the end fits into a compression fitting that connects to the superheater tubes. The large hex fitting on the right end in the photo is the compression nut. Tthe 3/4" hex is visible to the right of the nut and the short 1/2" OD tube to the right of the 3/4" hex. The challenge with making this piece is to get the length right as there is little room for variation.
This photo shows how the throttle rod runs from the steam dome through a bushing in the steam manifold support. The 5/16" compression fitting in the side of the steam dome will hold a couple O ring seals. The end of the rod is threaded. The current plan is to extend the rod back to the area of the oil tank so that it'll be easy to operate from the engineer's seat on the tender.
Steam Supply Pipes: This shows the the steam supply pipe to the left cylinder. The angle compression fittings on each end are 1/2" tube to 3/8" male NPT. The long elbow is silver soldered to the pipe. This 1/2" OD copper tube (also known as 3/8" copper pipe) and the WROT copper fittings were obtained from McMaster-Carr. The local hardware carries the more standard 1/2" and 3/4" copper pipe and fittings but not these 3/8" pipe nor the 5/8" pipes used on the exhaust.
This is a good place to end this page. The construction of the remaining parts associated with the boiler and smoke box are described in the Heisler Boiler Construction III page.