DHR B Live Steam [ Part 2 ]

The Darjeeling Himalayan Railway "Class B" Locomotive in 7/8ths Live Steam

Part 2

The starting point for the loco is the frames. As much as I try to design ahead there are still issues that are missed along the way that seem to come back to haunt you. The first set of frames that I had water jet cut were great, BUT (nothing worse than that infamous BUT to throw a wrench in the works) I had designed the first set of frames as per prototype. This is normally an option and in this case keeping the shape and consistency of the rear half of the frame was a problem. The rear portion of the frame was a large U that wrapped around the leading edge of the boiler. On paper and cad it seemed a good idea, however in reality the accuracy of the bent curve posed a couple of problems in keeping everything parallel and square. My second solution was to machine a spacer out of brass that had the curve machined into its design. This when complete looked proper and at the same time it allowed for a great array of functions, including a boiler bracket.

Here are the refined cad designs that I used for the loco frame. I had the frame laser cut as apposed to water jet cut when I did the second run. Cost wise the laser cutting in more economical. In comparison the laser cutting is far more accurate for small holes as compare to water jet. In finish quality the water jet far exceeds laser cutting. The edges are almost like a knife they are so smooth and sharp. The other advantage to water jet is the lack of edge hardening that laser cutting develops. I did feel that being able to have all the required holes cut at the same time advantageous and that is primarily what led to having the frames laser cut.