Saturday, 14 April 2012

Toy train progress

I recently bought a copy of Martin Evans/LBSCs book on how to make a model 9F, which made me realise I should probably finish Tich first! This design has a very sad point of interest-LBSC died before he finished it, so Martin Evans took it over. If you've not seen my previous entry on LBSC, look him up- his writings are a great read even if you skip the loco making bits.
Anyway, back to Tich. In a moment. First, I've started rebuilding the bottom end of my shed. This will be my machine shop, locked up and insulated from the rest of the shed to keep my equipment nice and get my micrometers out my bedroom. The old wooden pile came down in a day with the help of Nathan the CBR125 breaker, and it was burned 2 weeks later in a pretty awesome party. Between the two, I reckon I dug 5 tons of soil out.

The brown hairy rug decided to be my foreman throughout, ensuring I'd thrown enough balls and all bags of soil were properly peed on. They'll take him on at work next week.

Anyway, having got that out the way I started on Tich's smokebox, or if Andy's reading "the bit where the face goes". To make it I had a bit of brass tube, a casting for the front, one for the door and one for the saddle, which it sits in. The front was easy enough, first I turned to a hammer-in fit in the tube. I then did that, and mounted the lot in the chuck to machine the front and the radius edge. Here's a handy tip for anyone holding large, thin wall tube in a 3 jaw chuck: make a spider by drilling and tapping every other edge of a nut, then fitting bolts to suit. Put it in the tube like so, with the bolts nipped by hand so it sticks in squarely:

You can then tighten up with the bolts exactly under the jaws, avoiding either bending the tube or having it do an alien face-hugger impression when you start the lathe up.
I made it this way as I wanted to avoid a great big lip on the front of the smokebox, where the tube sits proud of the casting. A quick google the next day showed that I shouldn't have, they all look like that-but I'm making it, and I think it looks half-arsed. Now I've said that I've got to make everything perfect :S
The convex door shape required a new technique. LBSC recommends using both slides to create the shape as best as possible, which is doable. Instead, I made a tool a bit like a wood turning tool out of a blunt file-grind some clearance and a good, flat edge on the end. I then clamped any old tool in the toolpost, to act as a rest, and cut the door freehand, pretty much how wood turners would. Make sure the rest is very close to the job, have an emergency stop close to hand and dial 99 on your phone just in case.

The smokebox saddle needed facing off flat on the milling machine, which is a shame as I don't have one. However, another common trick is to use the lathe. In this case I made a fly cutter from a big lump of steel that was lying about, and a small bit of square HSS. For those who don't know, a fly cutter has one cutting edge offset from the centre. You can use it to face off big things, though nowadays you can get some pretty huge indexible insert cutters that are far better. And pricier.
Here is said cutter in action. I used such a chunky bit of metal in the hope it would be nice and rigid, which gives better cutting. What I didn't account for is the carriage lock on the lathe being pretty knackered, so it just pushed that back instead-spent all evening taking about 1mm off. Still, one more thing learnt...