Out of the 6 wheel castings two were very hard and although I removed very little from the
rear faces, I found that when it came to the fronts, I did not get right through the hard
skin.Having completed the basic shape as far as possible, I bored the holes for the crankpins. To do this, I made a spigot to fit the centre which had a cross to mark its centre. This I did in the lathe with the tool at centre height. From this centre mark I was easily able to measure the correct distance to the crank pin hole as I have digital readout on my mill. I was therefore able to get an accuracy to a thou on all six wheels.
The next progression from this was to use another spigot in the pin hole and rotate the wheel to create the boss for the crankpin. The picture shows this. I found that it was impossible to get rid of all the casting sand from the front so I had the lot grit blasted which gave a beautiful,dull grey finish albeit, a little rough, which happens with cast iron. Since it is painted black, it shouldn't be too obvious.
The castings were fairly good, although there was the odd pit as can be seen in the photo. I have left quite a bit to turn off to make the flange as this was held in the 4 jaw chuck. The finishing cuts to be made when attached to the axles.
While I waited for some material, I had a change and did some other work which is much
easier when the loco is upside down. Namely, the pipework. As can be seen in the photo,
good use was made of standard 10mm copper plumbing parts, which are quite cheap and means
that right angle bends are easily coped with.
The twin pumps draw water from the common linking pipe which is necessary as the well tank has an axle passing through it. At the same time, I added a drain plug at the lowest point. The twin pipes connect to the clack valves of the pumps. I added a plug to the base of each clack, so that should the ball seize up at any time, it can be pushed free through this plug hole.
Several of us were discussing the materials necessary for the crank pins. One experienced member advocated silver steel as he always used it. However, another member proclaimed that that was the wrong material as it was a tool steel and therefore brittle. He advocated EN8, this being a hardenable steel. The drawing said case hardened mild steel.
So, I elected to go for EN8 as no hardening was required and yet it could be turned in the lathe. The quantity and size of the silver steel was quoted at £28 at an exhibition and £14 at a local supplier. However, the EN8 from the same supplier's off-cut bin was about £1-50 with plenty spare!
I wasn't happy with the Romulus crankpin design because to remove the coupling rods would mean
that the crankpins would have to be removed first, unless of course, you used the alternative
marine style coupling rods. I'm not a great fan of these on locos. The crankpins were a
press fit and held with a plate washer and screw on the inside, much as I've done but mine
is on the front. I used Don Young's method which can be seen in the photos.
The three pictures are the leading and trailing crankpins; the driving crankpin being completely different. The last picture shows that after using Loctite, I've drilled and inserted a pin down the join, again after Don Young's method. He doesn't favour inserting a threaded plug as shown on the Romulus drawings. I used a little Loctite and hammered the pin in.
QUARTERING
These two pictures show how I have done the quartering. On the left, the block supporting
the crankpin has been machined accurately. In this case, the centre height, 136mm minus
half the diameter of the crankpin; 3/8". I managed to mill this to within .02 of a mm.
The block at the other end has been made to just fit in and sit on the lathe bed. A slot
has been cut and milled accurately to 3/4" wide. The crank pin sits in this with no side
play and wedged in the lathe bed, provides a stable set up. All I have to do now is Loctite
the wheel in position, wait until set, then drill and pin as before. All three axles will
be identical and any small errors will be common to all three. After that, the final cuts
can be made to the wheels to make sure they are of identical diameters etc.