< Smokebox >
The smokebox shell was made from a seamless brass tube. As the I.D. of the tube is slightly larger than the O.D. of the boiler barrel, the tube should be cut an inside step. Two cherry wood disc and an arbor were employed to chuck the tube between the center of the lathe.
There are many holes on the smokebox, for chimney, blast pipe and steam pipes. They were bored in the lathe by drill, boring tool or end mill. Especially the last one is vital to bore slantwise holes. I marked out also opposite side of the hole for lining up between two centers in the lathe.
The smokebox door and the ring are made from gunmetal castings. The ring is easy turning job because it has no "hinge lugs" cast on. Its O.D. is turned to a hand push fit to the smokebox. On the other hand, the door is thin and curbed item which requires careful turning as follows.
Chuck the spigot, turn the sealing face, saw off the spigot and reverse in the chuck. Then face off the boss and drill through. Next, a jig to hold the door is prepared and the curbed surface is finished with tapered turning and finally with a smooth file.
The door hinge straps were made from BMS square bars, soft-soldered onto a piece of other square bar. Chucking the bar, mill the steps, file around the bush and drill through. I left the strap part of the hinge slightly tapered, because I know a rapid door opening should bend a thin straight hinge easily.
The straps have to be bent to fit to the door surface. It was hard job because the straps were very tough! I did this with annealing, pressing and hammering many times. The holes for the rivet must be opened after the bending, otherwise the strap is folded at the holes. Incidentally, distortion of iron rivet head can be eliminated if you use copper block as anvil.
The brass hinge lugs were screwed from the backside of the door ring and silver-soldered. At the stage, the holes were not opened yet.
Parts for the door handle. The handles and dirt were made of free-cutting stainless steel.
The square hole in a handle bush is cut as shown in the photo; in every 90 degree turns in the chuck, a half-round cutter is moved to and fro by hand.
The dirt, which consists of 4mm dia. stem part and 8mm width triangle part, was made from 8mm dia. round bar. First, the screwed part and the square part were finished. For the latter, the bar was hold in a tool post and end-milled, with a square bush (like an axlebox) glued onto the bar for index rotation with a try-square. Then the opposite end for the triangle is milled to 4mm thickness. Next the thinned part was chucked in the four-jaws, the tip supported by tail stock center, and the reminder was turned to 4mm dia. Finally, the triangle's taper is turned and finished with files.
Now the handle can be used to fix the door onto the door ring, so as to drill the hinge lug through the hinge holes.
The brackets for the draw bar, made of brass, were screwed onto the door ring and silver-soldered. Then the smokebox door assy was completed.
Due to the modification of the chimney, the casting can be used only for the base of the chimney. The chimney body will be made from a brass round rod and silver soldered to the base.
The casting was partly finished and parted off. Note the inside step turned for the next process.
I used a brass disc fitted to the inside step so as to fix the casting onto the angle plate. Then the back surface was fly-cut to the outer diameter of the smokebox. It is important to line the miller spindle to the casting center, otherwise you will get tilt chimney !
The chimney body was partly turned and silver soldered to the base. The previous inside step is useful again to prevent the melted solder spread over the back surface of the base.
Finishing the profile in the lathe. The large radius at the joint was cut step-by-step and finished with a home-made cutter, a simple tapered disc parted off from a carbon steel bar and hardened. Incidentally the inner hole was cut with a long boring tool from both side of the chimney.
Filing the base to a correct shape. Note the protecting tapes around the chimney body and the tail stock. Finally the base was cleaned with an emery cloth and a brass wire brush.
Bush for the chimney fixed in the smokebox. Note the small tapped hole in the side to fix the chimney with a screw. The screw's tip is tapered and the chimney foot has a groove for the screw. The position of the groove is a little higher than the hole. Then, tightening the screw, the chimney is pulled downward.
The curved surface of the bush was turned in the lathe as shown in the picture. Again, the lining is important.
Now the boiler is picked up again. It needs expansion angles onto the both sides of the firebox. They were fixed with brass screws and coke with high melting point soft solder, because I don't want to have a silver solder trouble on the boiler any more! Once the boiler is coke with soft solder, you cannot silver solder anywhere and also cannot pickle the job. Because the soft solder is corroded by acid.
I did a hydraulic pressure test again. In this time I successfully raised the pressure up to 1.5 MPa without any leakage. It sounds easy but it was really painful time ! Incidentally, a stop valve between the hand pump and the check valve is useful here. It prevents backward flow and also you can remove the hand pump without dropping the pressure. A dental mirror is useful to check the inside of the firebox.
The smokebox saddle is made from a gunmetal casting. The top surface was fly-cut in the same way as the chimney's base. The width of the saddle was finished using one of the frame stretchers as a gauge.
The saddle fixed onto the smokebox with screws, the boiler inserted to the smokebox, then the whole job is mounted between the frames. Keeping the frames and the boiler parallel, it makes shallow countersink onto the saddle through the holes in the frames. I did this work with a powered hand drill. Note a copper tube around the drill as a "stopper". Then the saddle is removed, drilled and tapped for assembly.
The smokebox was completed, even though it contains nothing inside...