CRANK PINS
I finally got round to sorting crankpins for the fly-cranks, which are of 35mm silver steel
The only two really vital things are: a) to get the crank pins at exactly the same centres, and b) to get them parallel to the axles.
I tackled this by first of all welding a bit of 50mm dia steel (axle size) to a bit of heavy plate, and bolting it down to the drill/mill table - this jig obviously ensures that the fly cranks (when tightened up onto afore-said stub axle) will all be in exactly the same place as each other in regard to the drill .....as long as I totally stopped the table from moving.... which I did by clamping more steel plate underneath, either side of the table- making it impossible to move.
This formed the basis of my 'jig', on which I put on each crank in turn, the same way round, the same way up on the same piece of packing as when I drilled the 50mm holes for the axles. This ensures that the drill works in exactly the same plane as before (and if the quill was half a degree out before, then it is that same half degree out for this process - i.e. the bores end up parallel.....)

The crank pins (the front four of which have groves for circlips machined in) were centre drilled at both ends - the back end to enable them to be drilled out of the crank if necessary, and the front end 'just in case...', and then they were rose welded (again on the back face) into the cranks. They are removable if really necessary, but very secure and very firm!

A NOTE HERE..... Now, in 2007, I have found that one pin has broken its weld. This is due to the welding hardening the silver steel locally, and of course it doesn't get tempered! To be safe, I've removed all the crank pins, have re-bored the cranks, and will be fitting new pins from mild steel. If you are pressing the pins in, silver steel is fine - but if you're using heat - use mild steel (at 35mm diameter it should be plenty strong enough....)

COUPLING RODS
Some time ago I took the opportunity to get the rods profiled (with the main frames) at a cost of around £10 each - not bad for 25mm plate ready cut to shape! These needed cleaning up with a flexible pad on a 4 1/2" grinder, faces and edges, and then the joint of front and back rods (to allow articulation) machining. I'm doing a slight cheat with this, as I'm machining a 'half lap' joint (as we called it in woodwork many years ago!), and then adding a profiled piece to the outside of that to create a clevis (in double shear). The machining was tedious, but fairly straight forward, using a boring tool set to the required diameter (in this case 60mm) and taking 0.5mm cuts time and time again.....
The pin is 25mm silver steel, bored, cross drilled and tapped to allow greasing of the joint. The pin then runs in a plain steel bush in the centre rod. This pin is then silver soldered to the 25 x 3 plate which forms a keep for it. Not necessarily pretty, but quite practical.. The rods are now ready to be machined for the roller bearings.....

Incidentally, Aidan described a jig that his mentor, Tony Grice at Culworth Engineering used to use when sharpening drills. Very simply, it was an old lathe centre mounted on a bracket which has quite a high back to it. The trick is to sit the drill being checked onto the centre (large drills have a centre drilling already...) and then use each cutting edge in turn to scribe an arc on the back plate. If the drill was correctly ground, the scribe marks would be over-laid, but if it had been ground unevenly, you would end up with two separate scribes, which means the drill will cut over-size, and needs grinding true.
This is very easy to make, very easy to use, and improved accuracy no end (on the large drills). I am now resonably happy to sharpen drills over 1" dia with an angle grinder - knowing I can get them pretty good. Up till now I was paying £15 a shot to get them done professionally.

I've just spent more than a day machining out the coupling rod bosses to take the roller bearings (35mm I.D. and 55mm O.D.)..... building an 0-4-0 instead would have its merits...
The technique was straight forward though - mark, centre punch, drill lots and lots of sizes up to 50mm dia (makes my mill/drill grunt a bit..), and then open it out progressively to 55mm (49.95mm) dia with a boring tool (tedious, but nice and accurate).
I bored out one end of both rods first, and then welded a stub of 35mm steel (size of crankpins) to a plate, and firmly bolted it down to the far end of the table, fitted a bearing into the boss I'd already machined, and dropped it over the 35mm stub. This meant that I could ensure that the centre to centre of the rods would be entirely consistant.

Anyway, it has worked fine, and having tacked on some 6mm tubular spacers onto the fly cranks (to nestle the coupling rod bearings against) I fitted the rods on on side, slackened the adjustable horn guides off, rolled the whole thing up and down a bit, adjusted the guides, and tightened everything up! The wheels go round and round.....

I very carefully ( by measuring and chocking of wheels) quartered the driving wheel on the far side (not forgetting that the right hand usually leads) tightened the crank up, and checked it. I then fitted the second set of rods (with the other two cranks still loose), and repeated the same procedure from the other side (I always tighten up the cranks when they are in their vertical position, to ensure the rods hold them in absolutely the correct position), and hey presto! it has suddenly become a locomotive........

For security, I've now drilled and tapped the crank / axle joint M8, and fitted socket head screws (belt and braces job)

I'm about to paint everything in grey primer to stop it from getting rusty rusty on its trip to Brighton, and then the next job will be pistons, piston rods and crossheads (now flame cut).

'The Priest' looking smart in grey primer

I recently got the flame cut blanks for the connecting rods (approx £15 plus VAT each), and I've built them up with more laser cut profiles as shown in the photos below.
It's very easy - just grind a bevel (approx 6mm deep) on the edges to be welded (to ensure penetration), tack them on, check them, and weld them....
It tends to look a mess at this stage, but a quarter of an hour with an angle grinder, first with a grinding disc, and then with a soft abrasive disc gets them sorted. You don't get quite the finish that you can achieve with machining, but if they are to be painted it's quite good enough.

Hey presto! Ready for boring for bearings.

In another direction, I've fitted the brakes and compensated rigging - I've just got to sort the Brake Cross Shaft. The brake blocks were bought from the Engineers Emporium, and after a slight reduction in width courtesy of the band saw, they do the job very well. Brake hangers were laser cut for conveniences sake. You see the extensive use of bright bar welded to a plate and bored as plain bearings or spacers. This is fair enough for brake rigging etc., and should last donkey's years (with grease of course), but one obviously wouldn't use plain steel as a bearing surface in the normal way......

A closeup of 'The Priest's suspension (showing how simple it is....) note the grease nipple though, this feeds grease to the horn cheeks via a diagonally drilled hole. Again, very easy to do with a hand drill.

I recently made a slight change of plan - I've always liked two guide bars - upper and lower- I think it looks more distinguished some how... but the draw-back is (in this instance) that I won't be able to remove the connecting rod without taking off the motion bracket as well - as the rod is on roller bearings on the 35mm dia crank pin.
I've finally decided that in the interests of practicality that I should modify it to a single bar arrangment, and lose the bulk of the motion bracket. This was quickly done with my nine inch angle grinder with a cutting disc.
Incidentally, the gap between the slide bar and the back bolting flange is not an accident - I left loads of room for a packing plate that I can machine down to the measured thickness (instead of just shimming).

As you can see, the piston and piston rod is now in existance.
This was a relatively straight-forward job. The piston was machined in cast-iron, with two pairs of cast-iron rings fitted, and the piston itself bored with a five degree taper- machined at the same setting as the business end of the piston rod. (this makes sure the two tapers are identical and therefore fit. Remember how effective morse tapers are for holding tooling......) Machining tapers on these things is every bit as easy as machining shoulders - indeed easier..... I would therefore never do it any other way!

The Cross-Head end of the piston rod, however, was more tricky. It's really important to get the thread true, and so I put it in the lathe, centred it, and started screw-cutting the M22 x 2.5 thread on the lathe. I then took it out, and finished the thread with a die in the conventional way. I must say I didn't enjoy any of this with the stainless-steel.....Next time I'll do the cross-head end with tapers as well...

However, job done - I've made the gaskets and fitted it all. Valves Next!

-The piston Rods are 7/8" diameter stainless, with 5 degree taper over 38mm locked by M16 thread at the piston end, and 22 x 2.5 thread at the other-
- The slide bars are 40 x 25 bright bar, secured with M10 machine screws-

As a small aside, you'll notice the piston rod gland - in this size it's quite large - and I didn't want to waste precious gun-metal on something that size. I actually machined the sleeve/bore from 30mm dia gun-metal in the conventional way (can't use brass, as it'll wear out in five minutes flat), and then cut a bolting flange from a vast lump of brass half an inch thick that some one gave me years ago, bored it, and silver soldered the two together - so I'm only using gun-metal where it's actually needed.

'No.2' - 'The Priest' page 3