OO9 Ruston Proctor part 2 - chassis.

One of the reasons behind this build was to scratchbuild my own chassis, which has been an ambition of mine for quite a while now. Putting a ready made (or kit built body) on a scratchbuilt chassis might seem rather odd, but a lot of OO9 kits are designed for RTR chassis, some of which are out of production or just plain wrong for the loco modelled so learning to design and build my own running gear will have distinct advantages. And it should work out cheaper as well...

The frames are made from 1/4" x 1/64" brass strip, soldered together for drilling and milled down to 5.5mm deep. 1.7mm holes are drilled in the ends (10BA clearence) to allow the frames to be bolted together using 6mm long turned brass spacers;

The 10BA screws and nuts are removed after the spacers are soldered in place. Axle bearings are also turned on my Unimat. Note the milled cut-out under the frames, this is to provide clearence for the pick-ups. Also note that the turned spacers are cross drilled, these will be used to fasten the chassis into the body.

Motor/front bearing mount and rear bearing mount are made from the same brass strip. To locate them I fitted the axles with the gears in place, then used an off-cut of .040" plasticard to space each mount away from the gears. Checking the mesh was a tad fiddly, a case of tack then check with the gearing fitted in place before making the joint permament. The front gears are a little tight for my liking, but it runs without fuss so I'll leave alone.

Tenshodo 14:1 gears are used, the axle gears are supplied with a 2mm bore so I pressed them onto brass sleeves to reduce the bore to 1.5mm. The sleeves were made a sliding fit onto the axles, to be Loctited in place after the wheelsets were fitted. The worm shaft proved to be a fiddle to fit, mainly because of a lack of room due to my turned spacers. Sealed bearings are fitted both ends, held in place with super glue as Loctite wouldn't set, possibly because the bearings are stainless steel rather than the mild steel?
Here it is fitted up with the motor epoxied in place;

I've used one of Nigel Lawton's 10mm x 12mm Mini Motor's, these are rated at 12 volts so no resistor is needed unlike some of Nigel's smaller units. Power is transfered to the worm shaft using more of Nigel's components, a 1.2mm root pulley on the motor shaft and 4mm root pulley on the worm shaft, with a 6.5mm i/d drive belt. I'd rather have used a larger driven pulley but my chassis design wouldn't allow anything bigger between the frames, a design weakness which I shall just have to live with this time.

Wheels are Parkside 6.2mm disc. I wanted one side of the chassis to be live so that only one set of pick-ups were required, so on one side the wheels were modified by removing the tyre from the moulded plastic inner, and pressing the tyre onto a turned brass hub. I've done this before when converting Parkside wheels for split chassis use, described here.

Pick -ups are made from .315mm phospher bronze;

On the bench the chassis is a nice smooth runner, and once I'd adjusted the pick-ups its pretty good on my oval of Kato as well. I may yet swap the pick-up wire with thinner phospher bronze, to see if I can improve the running even more. When I fitted the pick-ups I soldered the motor wire on first using 188 degree solder then use 145 degree for the pick-up wire, so I should be able to unsolder the pick-ups without disturbing the motor wire. Thats the theory anyway...

So, thats my first scratchbuilt OO9 chassis. The basic design is nothing new, in fact its a bit of a cliche, and if I was starting again I'd do things differently, perhaps using with 4mm diameter spacers rather that the 5mm dia. ones that I used, which would have made fitting the worm shaft easier. It would also have been far better to shorten the frames at the front, basically cutting away everything ahead of the motor/bearing mount to allow a larger driven pulley to be fitted, but I wanted the chassis to be attached at the ends, for stability as the body is quite a bit longer than the wheelbase. Still, if nothing else it looks neat!

Next job is to mount the chassis into the body.

Paul.