Thursday, January 03, 2013

P Class history

Old chassisA few weeks ago, I was approached by the guy who runs out local club second hand stall to advise him on a couple of kits he'd had passed over for sale.

One was a bit of a surprise - an original P Class tank engine. Just like the one I completed recently.

I think this is an original Wills production from the 1960's. While the body appears to be the same, underneath the modeller is expected to use a cast whitemetal chassis.

The theory is that it's a good idea to supply the scary bit of construction as a ready to use part. The fact that it looks a lot like the solid chassis found under contemporary RTR engines is a bonus in the "not scaring the modeller" stakes too.

On the face of it, this is good. Look, the axles holes are even ready-bushed with brass bearings. How fab is that?

Fabness depends on the lump of metal. Whitemetal shrinks as it cools and although an expert toolmaker can work out how much shrinkage will occur, (using a Shrink Rule) it's not easy. Nor is it an exact science as different thicknesses will change different amounts. To make things worse, even if you unpack a perfect chassis from the box of bits, being a soft metal, twisting during construction, through something as simple as over-tightening the body retaining screws, will turn a sweet runner into a bag of nails pretty much instantly.

Finally, for good running to occur, the holes in the con rods should match the centres of the axle holes. Making the two parts out of different materials just makes this match harder to achieve.

All this explains why we now tend to find etched chassis. While they require construction and effort, the chances are the results will work properly.

The kit? Well, I understand it will be on the L&WMRS second hand stall for about £35, with room for negotiation.

1 comment:

James said...

Wills, IIRC, used to jig drill their chassis blocks so they would match the coupling rod centres - far better than some of the other efforts from the same period!

My Dad has an unbuilt McGowen LNER D49 where everything was whitemeatl - and I mean everything! Even the vale gear, so one slip and it would like 60532 Blue Peter once did! The body, on the other hand looks superb, so one day it'll be mounted on a Comet chassis. Some older kits still have a lot going for them if you're prepared to put the effort in!