Moving onward and after successful clearance testing on Sunday with the rear truck (more details anon) the next step is the brake gear, on soon to be next step as I may do the new smokebox saddle first.
Before the brake gear can go on the wheels need trimming back, there's very little clearance between the rims and the brake hanger pivots so the flanges need trimming back first of all and whilst doing that I take my obligatory 10 thou off the back to give extra side play at the rail head...not at the frames which are still virtually zero sideplay.
Traditionally I just stuff the wheel on an axle into the chuck but with 6'9" wheels the rim was flexing too much and Slaters wheels are a pig for being square on the axle in the first place! So, it was time to step up to turning wheels correctly...nearly...I always try to find short cuts LOL.
First off acquire some brass bar, good old bay of E and a nice message to the supplier found two discs of 45 mm bar 18 mm thick drop through the door today so it was off to the lathe for some turning work.
I fitted the reverse jaws and had hoped that the discs / pucks would just fit in the outer jaws, but it was not to be, the minimum closure is about 48 mm.
Thus they need to go into the middle set.
Overall I'm not that happy with that much jaw sticking out of the chuck and its only a couple of turns of the chuck key before they drop out so decided to just take a bit off one end so that the jaws tighten a little better.
I can always take off more at a later date and may use the smaller backside as the base for smaller dia wheels and machine it like the front.....below.
Swapping the puck round I cleaned it up all over, faced it off square and added a depressed centre and drilled out the centre to take a Slaters 3/16" axle.
On the smaller dia I punched and drilled a 3 mm hole in a machine vice on the pillar drill and then tapped 4 mm all the way through to the centre hole for a retaining bolt to hold the axle in place.
The axle sits just proud of the depression and can be moved in and out as deemed necessary.
The reason for the depressed centre is apparent here, when facing the rear face (badly in the case above!) of the tyre the boss and crank casting stands proud of the rim so will sit in the depressed area and ensure the rim is hard up against the puck for full support.
I'm not sure but I'm guessing the thickness of the boss and crank casting vary in thickness, hence the adjustable axle retaining screw, you will always be able to adjust the axle so that the rim sits flush with the puck. I also centre punched the chuck to align with the retaining screw so that the puck always goes back in the same place.
Having done the rear and skimmed the rim to more pleasing profile it was time to do the front.
This needs to be done with caution, 2 thou at a time and you can safely.....so far.... take off 10 thou and maybe 14 thou at a real push before the rim becomes too thin. All this skimming produces wheels that are almost exact thickness for the real deal, the wheels start out at about 3.9 mm thick and end up at 3.25 mm, the real loco is scaled at 3.14 mm.
Bit hard to tell, but the centre wheels are the correct size between the two other axles.
There are other ways to turn wheels but this is the most comfortable for me and there's plenty of traction from the axle through the spokes to the rim if you take nice easy cuts, 2 thou or less.
Once all three sets are done I can then add the hangers, cross beam and start fabricating the brake shoes as the insulation unlike the A1 tender will be here, that's the plan anyway. I also need to take a sliver off the retaining screw boss at the wheel centre and the boss for the crank pin, the A3 wheels are not flush but the boss's are not that large.
The leading bogie wheels are the same profile as the drivers, so the thinning there will help greatly with clearances up against the now correct profiled outside cylinders, even with their prototypical cut out at the rear face.
In other news, CAD work progresses on the tender etches, though it's not full steam ahead yet as I cannot decide on 15 or 18 thou NS as the source material.
I'd like to keep all the art work on one size material, even for the locos and have already decided on laminated main frames, but, it's the combination of two full thickness's or one full and one half etch with exterior detail, both have merits and only one combination is true scale frame thickness, the one using 18 thou NS and that's quite a hard material and thickness to bend easily elsewhere on the model (footplate, tender cantrail etc)
Anyway, Onward!
)
I've only skipped through the mags on my desk and a couple of books to check other locos, still have all the big detailed volumes to trawl and other mags that show just one or two A3 images as opposed to articles on A3's which I currently have to one side. But A4's should have from factory, one large and one small.
, now that drawing I'm sure does exist 
