Sunday, 24 January 2010

Remedial work

Buoyed by my success with the tiebars the other day, I decided to have a crack at rebuilding one of the common crossings on the layout. I'd been in two minds about tackling it for some time but had kept procrastinating. The problem was that I'd used thin metal strip rather than copperclad strip to connect the vee and wing rails, so the crossing had required some additional packing to bring it up to the correct height. However, I'd rather overdone the packing so there was a bit of a hump in the centre of the crossing. At the time I'd thought it 'would do' as it wasn't immediately obvious on looking at it, but as usually happens with such things, the more time passed the more I realised it really wasn't ideal at all and that the problem was quite evident when running stock over it.

I managed to extricate the offending crossing without damaging the surrounding track. Then, using the soldering iron, I removed the metal strips so the wing rails were detached from the vee. Then came problem number one. All my vees were soldered up using 188 degree solder and the only thing that stopped them coming apart when soldering up the rest of the crossing was by not dwelling too long with the iron. Well, you guessed it, in the course of unsoldering the crossing, the vee came unsoldered too! Darn! Lesson number one - silver solder your crossing vees so they don't come apart later!

Some time later I had reformed the vee to the correct angle (one of the EM Gauge Society crossing vee jigs would really have made this so much simpler, I just don't have any way of getting hold of one short of going to an EMGS show - unless any of you good readers happen to be an EMGS member and could get hold of one for me....?)

It was time to fix up the crossing again. Previously I'd done this by sticking a printout of the crossing template (from Templot) onto a piece of chipboard with double sided tape, stuck the connecting strips to the template using double-sided tape, tinned the strips, tinned the underside of the rails, then positioned the vee and wing rails using drawing pins to hold them in place before applying heat from the soldering iron to cause the tinned surfaces to join together.

There were two problems with this approach, although I'd sort of managed previously despite them. (1) Trying to push drawing pins into chipboard is pretty difficult and its even more difficult as a result to get the straight (coupled to the fact the large head means you can't see how straight they are very easily!). (2) Just relying on the tinned surfaces melting together to hold everything in place is a bit hit and miss.

So, this time around I replaced the chipboard with a cork floor tile (soft enough to make pushing pins in much easier but form enough to hold the pins in place), and replaced the drawing pins with quilters pins (the local craft shop had all sorts to choose from), these being much longer (although there is the risk of them bending, even when pushing into cork, if you're too rough with them) allowing for more pins to be used and with greater precision to hold the rails in place. Also, although I still tinned the copperclad strips, I used lots of flux and a blob of solder carried on the tip of the iron to make each joint - much better.

However, all this being said, I have to confess it still took me several hours to get the job done. Lesson number 2: always check, check and check again to make sure angles, measurements and alignments are exactly correct - one thing I keep on being made aware of though my own mistakes is the really small tolerances you have to work to in P4. There's a tendency to think "It'll do", but, as I've already said, this soon comes back to bite you! I had to take the crossing apart and start again several times because things weren't lined up quite right.

Even now, after placing the rebuilt crossing in situ, I realise that the angle of the vee is slightly too acute - it's only a fraction of a degree but enough to be obvious when sighting along the adjacent rails.... the question is is it enough to merit taking it all apart again, or can I get away with leaving it...???

1 comment:

  1. Hi Matt,

    Are you sure that you mean silver solder?

    That needs micro-torches and fire-bricks and stuff like that. It's really a model engineering discipline (or for manufacturers) and not one that is often found in smaller scales.

    You would get good safe results with the vee assembled with some ordinary high temperature solder like Carrs 243C. Then you can use normal 188C stuff for soldering around it.