Although this may seem a short post, it represents a very big step for me! I had been seriously concerned that I would not be able to construct a chassis with sufficiently well-aligned axles, within the constraints of my own abilities and my lack of any real workshop facilities - just a desk and Dremel drill on a stand.
When one builds a kit, the designer has already made lots of difficult decisions for you. A scratch-builder has to think out every little step for himself - what metal to use for the frames, where to position the spacers, and so on. I decided to cut my frames from 1mm x 6mm brass strip and to hold them apart by three Markits-type spacers. Since one of the driving axles is close to the centre point of the frames, I had to decide where to place the 'middle' spacer. I chose to put it ahead of both driving axles, in case the space between them was needed for motor mounting purposes.
Next decision was how to align the frames for drilling the axle and spacer-mounting holes. I have read the suggestion to solder the two frames together, so decided to follow this approach. My iron is a fairly basic Maplin 'solder-station' and, by trial and error, I have discovered that a temperature setting of 285°C works well for me, when using lead-free solder, without too rapid tip-oxidation while 'standing -by'. I've no idea how accurate the temperature read-out is, so other irons may differ. There are convenient buttons on the controller, to switch to pre-set temperatures, and I usually switch to 200°C if I'm not using the iron for a reasonable period. This keeps it warm between uses, without much oxidation. I clamped the frames together, applied some phosphoric acid flux to the ends, and soldered them together. This was fine for holding them when drilling the 2mm pilot holes but, when it came to opening out the axle holes to full size (1/8"), the drill tended to push the frames apart a little, so perhaps I should have soldered them together all along their length. I wasn't sure that my iron had the 'beef' for that and whether I would get them apart again!
I measured the positions as accurately as I could with a metal rule (marked in 1/2mm graduations), scribed guidelines with a small diamond scriber, and then centre-punched the holes for drilling. I used a 2mm drill in my Dremel mini-drill, mounted on its vertical stand. I aligned the drill by eye and held the parts in position with BlueTac and adhesive tape - supplemented by my fingers. Eye protectoirs are essential, since tiny specks of brass do fly about when drilling. I applied a drop of very light oil, which seemed to help the drill to go through quickly and cleanly. Once all the holes were completed and I had checked that they all seemed to be in the right places, I applied the soldering iron again, to separate the two frames. Then I cleaned up all the faces with needle files.
The spacers screwed in easily and seemed to be well-aligned (I have yet to counter-sink for the screw-heads) but I knew that the acid test would come when it came to fitting the axles through their bearings. I had to use a larger power-drill to open out the axle holes to 3.5mm and then I used a circular needle file to open out the holes very carefully, until the bearings were a firm push fit (with pliers). I smoothed off the ends of the (Alan Gibson) axles and gentle tapped them into the bearings. Everything worked --- they slid into position smoothly between the frames. To say I was relieved would be a great understatement. Actually, I was b----y amazed
With that hurdle crossed, I can turn my attention back to the 'body' and , in particular, to obtaining the various fittings that need to be added. One very prominent fitting on many of these early engines can be seen just behind the chimney. I remember, many years ago, that I found it quite difficult to identify this item, so I'm happy to pass on that it is a displacement lubricator for the cylinders. It was placed in that position for ready access to a steam supply but later, the fitting moved to the sides of the smokebox. Later still, these lubricators were controlled from the cab and led to another fitting that puzzles some visitors to GWR footplates. There is an item in the roof that looks rather like an electric cooker element but it is not there for crew comfort - it is the condenser for the displacement lubricator in these early 20th-century engines.