|Assembly and Alignment
||1. Wheel Assembly
||Before I could assemble the wheels to the axles, I had
to fix the coupling rods pins into place. These were a light press-fit done
on the drilling machine but, belt and braces, I used a locking screw to
keep them in place. The wheel was held on the pin using a collet block.
The block was then loaded to the milling vice and an M3 tapped hole made
on the perimeter of the pin. There is an M3 grub screw down the hole.
||Following on from that, I needed to fabricate the balance
weight plates and these were cut from 20swg mild steel for the backs and
16swg brass for the fronts. I've also engraved the wheels as left driver,
right driver, left coupled and right coupled so that they go back in the
same place after any future dismantling. The front axle was made at the
same time as the bogie axles, so no need to cover that again. I did need
to put the keyways in the end, though, and converted the fixture I made
for the Britannia axles. It just fitted end-to-end which saved having to
make a whole new block.
||The wheels are kept in radial alignment with the keys
and I have set a locking screw down through the hubs at 20 degrees to keep
them pressed back against the shoulder. The wheels are a stiffish fit to
the axles but don't need hammering on. No doubt I will get told off for
doing this as well but I want my wheels removable. The balance plates have
been drilled and fixed with 8BA screws and the gullies between the spokes
can be filled with some laed or printers metal, whatever low-melt material
I can get hold of. Once cast and set, the fronts of the screws will be sanded
off flush. The bolt-heads on the back will just be painted over.
|The axles have been asssembled, set into the
frames and the coupling rods fitted on. By some stroke of good fortune,
the wheels turn with just the tiniest high-spot at one point in their revolution.
This should work it's way clear after some running time.
||2. Building the Cylinder Block
||The steam chest sits between the two cylinders
so there is no access to the valves once the cylinders are assembled. Because
of this, I needed to make sure that I knew exactly where the valves were
when it came to timing everything and I have already made a pair of access
ports at the front of the steam chest for measuring things. I did each side
separately by putting the studs in one of the cylinders and fitting the
steam chest over them. Because they are a fairly tight fit, I'm confident
that the steam chest will return to the same position on re-assembly. With
a piece of 1/8" gauge plate fitted to the back port, the valve was pressed
against it and the distance measured through the first access hole. The
packing was then placed in the front port, the valve pressed against it
and a second measurement taken. With the average of these two figures written
down, and with all the other dimensions already measured, I now know when
the valve is exactly in the middle of the two ports. By repeating the process
with the other cylinder and it's valve, I have accurate measurements for
both of the valves once they are buried within the steam chest. One of my
older calipers was modified to enable these measurements.
||3. Adjusting the Pistons
||The next job undertaken was to adjust the
positions of the pistons and lock them to their piston rod. The first thing
to do was find the exact positions of front dead centre and back dead centre
on each side and I used the same method that I used on the Britannia. I
did a fairly comprehensive write-up on the method HERE
for anyone who may be interested. With the loco resting on it's wheels and
with the axleboxes packed and clamped at the calculated ride-height, the
approximate BDC postion was found by eye. The loco was then rolled forward
by about 30 degrees and a DTI zeroed against the front of the crosshead,
at which point the wheel was marked with the special scriber which, surprisingly,
had not got lost! The loco was then carefully rolled bacwards until the
crosshead went round the corner and came back to give the same reading on
the DTI. A second line was scribed on the wheel and the centre-point between
these two lines found using dividers. This was then centre-popped. The process
was repeated on the other side to get that BDC, then the loco was rolled
forward and the FDC's found for both sides (DTI measuring the other side
of the crosshead, of course) and these also centre-popped.
|I had put an M3 grub screw in the sides of
the crossheads to retain the piston rod and these came into play now. With
the front covers off the cylinders, each wheel was set at FDC and the piston
set at 1/8" from the front face. The shaft was locked with the screw, the
wheel set at BDC and the piston checked for the correct 2.1/8" from the
front face. With both sides correctly placed, the complete drive assembly
was removed from the frames and set up on the angle-table. Holes were then
drilled and reamed to take a pair of 1/16" taper pins for permanent fixing
and the grub screws removed. I didn't take pictures at the time but this
later photo shows the crossheads pinned.
||4. Next Item...