Friday 26 October 2012

Stumped by a Coffeepot...

For the first time since starting the build of the Coffeepot, I've hit a genuine, can't-see-how-this-works, problem that re-reading the instructions won't solve...

The crossheads are two very nice lost-wax brass castings. After cleaning them up, and straightening the piston rods, they are united with the connecting rods by passing a pin in the back of the crosshead through a hole in the end of the connecting rod, and then soldering a backing plate, well, on the back.

However, this is a picture showing the pin and the hole:

Crosshead 004.jpgC

You will see that the hole in the connecting rod is far too small for the pin. Indeed the pin is almost as wide as the rod-end itself... By way of scale, the total length of the crosshead is 14mm, so I don't have a great deal of metal and room to play about with.

My initial thought is to grind out (as I can't get a file on it) the pin at the back of the crosshead. Then I will drill a (say) 0.4mm hole through it, and use a brass lacemaker's pin to make a new pivot point.

Before I get out the heavy engineering tackle, is there anyone here that has either:

(a) built one of these Coffeepots or a similar Neilson and got this arrangement to work as designed, or
(b) can tell me that I've missed something blindingly obvious, or
(c) can suggest an alternative solution?

This isn't a deal-breaker by any means. The parts are all still beautifully formed, and this is the first difficulty I think that I have had and it's nearly at the end of my second tiny High Level locomotive. Knowing how good Chris Gibbon's instructions are, I do still wonder if I've missed something somewhere. Anyway, as he's now a Scalefour Society member, perhaps he can chip in on the Society's Web Forum and tell me where I've gone wrong...

Oh, and when I have it all sorted out, I've already made the clothes peg clamp to hold it all together to be soldered...
Crosshead 005.jpg



  1. Whin I built mine ( I just put the cast pin through the connecting rod. I don't recall any problems - but then it was a long time ago.

    Your photo would seem to suggest something has changed. Personally, I'd find someone with a tiny pillar drill and replace that pin with a brass dressmaking one. You'll struggle to go trhough without power, hence the pillar drill.

  2. Hi Phil,

    Thanks very much for the confirmation of how it should work. If you have a quick look at my very next post, you'll see both the issue and the fact that it can be easily solved.

    I do have a very good pillar drill - a Proxxon 220 - which I bough a year or so ago when I saw at a Missenden Modellers' Weekend just how easy they made tasks. Thankfully, in this case it won't be needed.