Tonight I have been doing a little planning for what I hope will be the first of several scratchbuilt locomotives for Hull Bridge. The Stirling F3 (LNER N13) was introduced in 1913. An 0-6-2T locomotive, the last example survived until 1956. Indeed 69114 was the last H&BR locomotive running on British Railways. In the time frame of the layout, the loco would actually be fairly new. As similar lower capacity loco, the F2, had been introduced in 1901, but they were mainly seen at the other end of the line working in the Barnsley coal fields.
Anyway, I have been trying to rustle up a working drawing to enable me to fabricate the mechanical element of the model. I scanned the drawing in HMRS book Locomotives of the H&BR and blew it up to 8mm:1ft, the original having been 4mm:1ft. I then used the tables in the 2mm Handbook and my rudimentary drafting skills to get some idea as to where gears/motors etc would fit. After a couple of attempts I came up with this:
The gear on the wheel axle is a 25T M0.3. At 8.1mm dia this should be okay with the 9mm driving wheels (I hope!). This meshes with a 14T gear on a lay shaft combined with a 30:1 worm/gear set. I was very taken with Tim Watson's method of mounting a worm shaft in a solid block screwed to one frame, so I thought I would incorporate that method. The ability to tweak the mesh slightly is attractive to me as a very non-technical person. The motor, a Nigel Lawton 6x12 could sit in the bunker and drive via a UJ shaft. This should leave the cab area fairly clear. A DCC chip will be mounted on top of the motor and the whole covered with a load of coal.
I think my main concern is that the two shafts are quite off centre in relation to the short distance between them; c8mm for a 1.5mm offset. I see two possible solutions. 1. Slightly tilt the motor up and the worm shaft down. This might seem easy, but I'd need to be careful as to the worm shaft mount and it would probably need to be a different shape to avoid fouling. 2. Recess the left hand side of the worm mount so that the shaft can be shortened. I'd need to watch that I didn't make the mount weak in doing so.
Does anyone have any thoughts? Have I made any obvious boobs that mean I need to start from square one? Thanks in anticipation!