Another A1 models diesel - part 2 chassis.

This is my second home brewed 009 chassis, and in the main the chassis follows on from the my first attempt at a scratchbuilt 009 chassis, seen here.

The frames are made from 8mm x .3mm brass strip, two sides being soldered together so that they can be drilled for the axle bearings and spacer locating holes. Bearings were turned on the lathe as were the spacers, lathe ownership does of course mean that I can produce the parts that I want and not rely on commercial sources. These spacers (6mm wide) are both drilled through and crossed drilled so that they can be used to hold body and chassis in close harmony as well as hold both frame sides together for soldering. Here are the frames clamped together, bearings soldered in place, ready to have the spacers soldered up once I'm happy that everything is nice and square;

Note the lengths of 2mm dia. silver steel being used to check that both axles are in perfect alignment (I'm using 2mm axles).
However, when I test assembled the chassis with the layshaft loosely supported by the motor and bearing mounts it became obvious that fitting the layshaft into the chassis was going to be rather difficult...

I didn't allow for a spacer being in the way. Ideally I want to be able to assemble the layshaft before sliding it through one end, the worms being small enough to fit through the front bearing hole, which is drilled 4mm, to suit the roller bearing that I'm using at the pulley end. My solution was to remove the turned spacer from one end and replace it with one made from brass strip, suitably drilled to attach chassis to footplate. Here's a pic. of the modified chassis frame, next to the front motor and layshaft bearing mount and rear bearing mount;

With the layshaft and axles in place, complete with gears, the front and rear mounts can be tacked in place. The gears need to be fitted at this stage to check that they're meshed correctly. To stop any stray flux corroding the steel axles I smeared them in oil. Once I was happy with the position of the mounts the layshaft was removed (slid out through the front mount) and the mounts soldered up. I did manage to solder up the front mount slightly wonky, but the beauty of soldering is that any joint can be adjusted.
Here's the chassis with the axles and layshaft trial fitted;

After I was happy with everything, I did double check with the gears re-fitted after the mounts were soldered in place, I added two little triangular strengthening brackets (made from scrap etch) to the motor mount to stop the motor vibrating. This is a problem on my first chassis, it doesn't affect the running but the the unit is noisier than I would like. At the same time I soldered in a spacer in the middle of the chassis to hold the pick-ups in place;

The mounts and pick-up spacer are made from 6mm x .5mm brass strip.

When I made the wheels I drilled them out to 1.9mm, I wanted a light press fit on the 2mm dia. axles so the plan was to broach them out to just under 2mm. This method has so far worked well on previous locos, which have had axles varying from 1mm (Kato) to 1/16" (Saltford) diameter. This time though I had trouble, two of the wheels had a pronounced wobble*. To remedy this I took the drastic step of mounting the wheels in a collet and drilling them out to 3mm. Then I turned a length of brass bar to 3.05mm and pressed a wheel onto the end. After a quick check that everything was concentric I drilled the wheel to size and parted it off. Repeat for the other wheel. Again they were broached to a press fit. My thoughts now turn towards drilling and reaming wheels 1.5mm and using 2mm axles with the ends stepped down to suit. This would also set the back to back.
Once the wheels were in place and I was happy I assembled the layshaft;

The roller bearing at the pulley end was simply glued into its mounting hole with cyano. There's a tiny spacer between that bearing and the pulley, one of the smallest parts that I've turned measuring a mere .4mm long. Gears are Tenshodo.
The motor is epoxied to its mount. Its a little Chinese 12v job bought for less than £2 a pair off eBay, measuring 7 x 16mm with a 1mm dia. driveshaft. They were so cheap that I bought 10, and this is the first time that I've used one. Nigel Lawton pulleys and drive belt are used, 1.2mm root on the motor, 4mm root on the layshaft coupled together by a 6.5mm ID belt.
The completed chassis;

Pick-ups are always a pain. A piece of copperclad sleeper is epoxied between the wheels, with the pick-up wire formed from 36swg (.193mm) phosphor bronze wire (from Eileen's). Solder the pick-up wire on the pad with 188 degree solder. Then the motor wire with 145 degree. And the pick-up springs off, heading for the carpet... Continue, holding everything in place with bits of wood, tweezers etc, until the job is done and the air has turned blue...

Before wiring the chassis up I held it in a vice and applied power to the motor leads, letting it run for an hour or so, making sure to change speed and direction a few times. The motor seems to perform well, although there is some vibration and noise, which isn't a problem and is what you'd expect for something that costs under a quid. It would be interesting to compare one with a higher quality job. Once the pick-ups were installed I ran it around my oval of Kato Unitrack (I don't own a layout). It ran well from the start, and continues to improve. I took it with me to a recent narrow gauge show where Will King very kindly gave it a test run on his layout (I was keen to see how it went through points), and again it ran smoothly. All very promising for future builds.

Footplate next.

Paul.

*In the previous two examples (Kato and Saltford) the bore diameter was smaller than the bore length, on these wheels the bore diameter and length are the same. A five sided tapered broach was used. Could the problem be in the relationship between bore dia. and length when using a broach? Hmmm.