Peckett "Y" Class - Framed! (part 1)
Entry posted by 2mmMark
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"I didn't do nothing wrong, but I always got the blame" sang Alex Harvey in Framed. Well, let's hope nothing goes wrong in making the frames for the Peckett. An inside framed 0-4-0 is a reasonably simple starting point nowadays.
When I first started in 2mm finescale circa 1982/83, something like this would have been much more difficult, as appropriately sized wheels & motors were just not available. Today, the 2mm finescale modeller is almost spoilt for choice.
Normally, you'd start with a drawing of the loco to get the frame dimensions. In this case, as I already had the body defined by the N-Brass etch, I worked from a photo and some known dimensions like wheelbase, wheel size and length over headstocks. What I did was scan and print the photo from the Railway Bylines article which gave me the ability to measure and scribble on a few key dimensions. Combined with the set size of the body, this gives a reasonably accurate starting point.
I then worked out how these translated to 2mm scale and made a few notes as an aide-memoire. I find Post-It notes handy on the workbench as they tend not to go missing at crucial moments. A calculator is also useful when converting between scales. Ignore the 2 places of decimals, it's just what the calculator and digital calipers said. I round up to the nearest "eyeballable" measurement
Some people plan out their frames in detail, I tend to "wing it" and pretty much make things on the fly. Sometimes that comes back to bite me but most times it works out OK. I do have a one chassis that has a redundant set of gearshaft holes...!
The first place to start is with a pair of coupling rods. This is the critical dimension for frame building. The rods and axle holes must line up. If they don't, you're on a hiding to nothing. Luckily, the 2mm Scale Association does a useful etch of rods. The Peckett has a 7ft 6in wheelbase which defines a 15mm distance between axle centres. On the etch are 14mm x 15.5mm and 14.5mm and 15.5mm rods.
I decided to use the 15.5mm section from these and not worry about the scale 3" discrepancy. Shocking inaccuracy, I know! As it stands the etch is 0.010" thick which is on the thin side for motion so I doubled up the rods by cutting the etch tabs, folding them over and soldering one rod on top of another. This gives a set of rods which can now be used to mark out the frames. Full cleaning up can be done later.
The frames are cut from 0.020" phosphor-bronze strip. The association sells this a convenient size for 2mm frames. Below shows a piece of strip and the shaped frames. Two pieces are laminated together by temporarily soldering at the ends. Making frames as pair like this makes life a lot easier.
The way to proceed is to drill all the required axle and gear holes before shaping the frames. Accuracy here is important so get the holes right before spending any time shaping the frames. If these key dimensions are wrong, you may as well throw the frames away and start again. If you spent time nicely shaping them with guard irons and the like, the pain is greater! Fortunately, the Peckett has a pretty basic frame profile. The photo shows the axle holes and also the hole for the intermediate gear. Gear meshing is made easy using the 2mm Scale Association meshing tool. This has a sliding shaft and two hardened pins on which the gears can be mounted and correctly meshed. Once the mesh is set, the pins are used to mark the position on the frames. Hopefully the photos below will elucidate. Meshing tables are published for all the Association's gear range but using the tool is much easier.
This shot shows how you'd overlay the rods on the frames to mark out the axle holes. I didn't photograph this at the time so it does show the shaped frames, contrary to my advice earlier.
I did all the drilling using a drilling machine. Apologies for the mention of machine tools! It's perfectly possible to do all this with simple hand tools. Machines make the job quicker and easier but they aren't essential by any means.
Here are the components for the chassis. The frame spacers are milled Acetal blocks, 1/4" wide. I got this idea from Denys Brownlee. These will give the necessary insulation for split frames and allow the frames to be easily screwed to the spacers. I prefer frames assembled in this way. I've nothing against soldered construction using PCB spacers, I've got a couple of chassis constructed this way myself but it's nice to feel that a chassis can be more "engineered".
The wheels are 7mm dia., the two coarser gears are 14 tooth 64DP and the worm & wormwheel are 28:1 100DP. I needed an intermediate gear to keep the motor level to fit the body and a 28:1 reduction will be sufficient with the small wheels.
For this chassis, one thing I've made is a simple jig, for which I got the idea in a recent Model Railway Journal article on 2mm chassis construction. It's simple a piece of melamine faced chipboard with 1.5mm rods inserted where the axles and gear shaft will be going.
It'll be useful to keep frames inline when assembling the spacers
and it's proving very handy for setting out the gear train and position of the motor.
That's where things stand at present. I have a set of parts which should be reasonably easy to assemble. The proof will be in the pudding!
Mark
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15
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