< Smokebox 3 >
I cut steps at both ends of the crossbar so as to control 'side play',
to be discussed later.
Door hinge brackets are made from steel rectangle bar. The lower is the original and the upper is modified one which will be discussed later, too.
Hinges are made from 6.4mm x 1.6mm steel flat plate, rolled at each end. They are annealed, hammered to U-shape on a steel former and finally hammered to P-shape with 4mm shaft and a step. After that they are cut in a desired length and drilled holes for rivets.
The smokebox door and hinges are temporary assembled individually and the hinges are bended by hand so as to fit to the door.
The hinges are fixed on the door with steel rivets. The hinge shaft is made from a steel rod and a nut. The nut is tightly screwed into the shaft and turned to round shape in the lathe.
Brackets for the crossbar is made from rectangle brass bar. They are screwed down inside the front plate. As they hold the end steps of the crossbar, the crossbar's side play is limited by them. Here the upper hinge bracket was modified because the upper nut had been in the way of the crossbar.
Chimney is pushed into the smokebox from top and secured by petticoat pipe at its bottom. To do this, I decided to cut screw threads in the chimney bottom and the petticoat pipe. No tap and die is available, so I cut them in the lathe.
The photo shows screw cutting tools. The left one is for inner thread and the right one is for outer thread. Each tool has 60 degrees tip.
The chimney is made from 40mm dia. brass pipe. Both ends are finished with 'fixed steady' and cut steps of 39mm dia. The upper step holds the chimney cap while the lower step goes through the chimney base. I chose 1.41mm pitch of the thread. It results 37.5mm bottom dia.
The outer thread is cut. I started the cutting with 0.1mm steps and ended with 0.05mm steps to avoid chattering.
The petticoat pipe is cut from a gunmetal casting. The photo shows cutting of tapered hole from the bottom.
The inner thread is cut from the top. The tool is advanced by inches until the chimney is smoothly screwed into the thread.
The photo shows assembled chimney. The smokebox top is round, so the petticoat pipe touches only at its left and right edges. But you can tighten it because there is the rigid chimney base against it. Incidentally, the chimney cap was glued on the chimney top with Loctite #648 (heat resisted).
The finished smokebox is fixed onto the chassis, sharing fixing bolts with the cylinder blocks.
