Nick Baines • Model Engineering
Cab and backhead
The backhead has radiused edges. In the past I have filed these, but because there was a lot more metal to remove I decided to try a corner rounding endmill. The blank was mounted on a plate that could be fixed to the rotary table at three centres: one for the firebox top curve and two for the concave transitions between the circular part of the firebox and the bit between the frames down to the ashpan.
First the two sides were done, then the rounded top. I was pleased with the finish, which needed very little fettling by hand.
Lots of holes followed for the ends of the stays (entomological pins, again) and mountings for the various fittings. The fiebox doors don't open, but I hope that they look as if they could.
Many of the fittings that you can see in the next picture are 3D printed in brass. A lot of the small details such as operating handles were too fine to cast or were finished in steel rather than brass, so I made them separately and added them. Even so, there was a considerable saving in time using the 3DP process. In the picture they are just placed in position to get all the pipework (copper wire of various diameters) correctly aligned. I painted the inside of the cab and the backhead before finally fixing them, because it was much easier that way.
The frame of the reverser was a 3D printing in nylon, and the rest of it was made the hard way. The design called for a left hand square thread. The external thread on the shaft was easier to turn than I expected, using a small parting tool and turning the lathe by hand. I chickened out of making the internal thread, so the reverser does not work.
The water gauges were the most fiddly parts. The top and bottom fittings are printed with operating handles from bent wire. The glasses are pieces of square perspex rod with tiny brass angles glued on all four corners. Getting those into place and holding them while the glue went off, without getting epoxy all over the visible surfaces, was quite a challenge.
I must say I am pleased with how the cab turned out, even if you can't see it so well when the roof is in place. The spectacle frames hold the glazing and will not be added until all the painting is done. I'm not sure how to add the gauge faces, I will probably draw them on a large scale and photographically reduce them to size.