The chassis has moved on a little since the previous post, a gearbox has been milled and the profile of the chassis has been milled/filed to shape.
The gearbox has a peg at the rear right corner which locates in a corresponding hole in the main chassis block, and a 12BA bolt secures the gearbox to the block at the front. Cutouts in the main chassis (and side frame) also locate the gearbox (although the one in the side frame is generous to prevent any shorts between the frame and the main chassis block when the gearbox is in place) - The gear box has extension cheeks that locate in these cutouts which also provides the layshaft of the worm wheel and first stage of the gear reduction.
Before I can complete the chassis, I need to determine how best to mount the motor. Initially, I had intended to have it as a separate item within the boiler, connecting to the worm shaft via a peg and bar arrangement which would hopefully cater for any slight mis-alignment between motor and worm shaft. A discussion with John Russell at the last Midland Area Group meeting has made me re-think this approach, and I am now considering mounting the motor on the gearbox plate making the motor gearbox a single unit. For this to work, I need to plug the countersunk hole in the gearbox plate and then drill and tap the fixing in the plate and open out the tapped hole in the chassis block to allow the gearbox to be secured from underneath.
However, before I go down this route, I need to progress the body a little so that I can see how the boiler will fit in place around a secured gearbox/motor assembly. I had previously built the boiler/smokebox, and the footplate/valances/buffer beams, (http://www.rmweb.co.uk/community/index.php?/blog/1009/entry-8625-2mmfs-gwr-metro-tank-part-1/)but to ascertain the boiler position on the footplate I need the side tanks. The tanks on the loco that I am building had quite pronounced rivets that I really felt needed to be reproduced, so I drew up the side tanks (complete with rivet positions) in Inkscape, the printed version being Pritt stuck to 0.006" nickel silver sheet, and the rivets formed with a home made "drop-rivetter" :
A tank top has been fretted/filed out of 0.010" nickel silver sheet around which the sides will be soldered. Before attaching the tank top part, some 1.5mm square rod was filed to the cab opening profile, and a piece of 0.009" guitar string soldered into a rebate filed vertically to represent the distinctive cab handrail found on this class :
In the next few days I will hopefully assemble the side tanks around the tank top, and attach this to the footplate which will finally allow the boiler assembly to be cut to shape to fit around the tanks which should then allow the goal of determining how best to fit the motor to be worked out!
There's nothing quite like winging it is there?