Welcome to
Steve's Britannia
5" gauge Adams O2 - Calbourne
Drawing E1(a). Drawing E1(b). Drawing E2(a). Drawing E2(b).
Drawing E3. Drawing E4. Drawing B1. Drawing B2.
Drawings S1 and S2 Boiler Assembly Assembly and Alignment Errors and Ommissions
Drawing E2- Wheels, Axles, Rods etc.
  1. Coupled Wheels  
I've managed to get a set of coupled wheels that were surplus to requirements from someone on the Home Workshop website and I'm pleased to say that they were quite decent castings with no chilling anywhere except on the edges of a few spokes. To start the ball rolling, each wheel was loaded to the independant 4-jaw chuck and the inside of the rim clocked as true as practical. Then the tyre was faced off to leave about 3/16" clear of the spokes and the o/d turned to well-above finished size to give me a reference for the next operation. Luckily, there is plenty of material on these wheels. I am not making separate tyres but I will continue to use the term to refer to the wheel tread.
Next, the 3-jaw S/C chuck was mounted to the lathe and the wheels loaded into hard jaws. I need to take another 60 thou off the front so they were faced off at 0.600". I'm working to the profile and dimensions on the Britannia drawings, rather than Don Young's, because they tally with the GL5 standard. The o/d was also turned to 5.175" at the same time and the axle hole drilled 12mm diameter. From this point on, I went to soft jaws and there were various operations to face the front, turn the maximum tyre diameter, bore and ream the axle hole, undercut the rim down to the spokes and form the radius at the root of the tyre. The soft jaws are only bored 1/16" deep so the centre is just for a bit of support in case of a dig-in.
The wheels were reversed once more and a 1/16" rim machined on the back of the wheel. Then the shape of the flange was machined on using a tool I keep just for this sort of job, a double-sided tool with approximately 2mm radii. The final turning operation was the coning to the wheel and the axle bore. These were both done without removing the wheel from the chuck to guarantee concentricity. The compound slide was set to 2.1/4 degrees and the toolpost returned to square. The tyre was turned using the compound, running out at the root of the radius and the axle hole was bored, two passes for trueness, to 13.8mm followed by reaming at 14mm.
The coupling rod pins were next and a simple fixture was constructed with a 14mm dimeter peg for the axle bore and a screw to act as a locating lug for one of the spokes. With everything clocked out on the mill, each wheel was centre-drilled, drilled and reamed 8mm. The last job was the keyway for the axles and I re-used a broach that I made about seven years ago for the Britannia wheels. I did have to modify the guide bush, though, and make a new alignment peg for the coupling pin hole. The setup can be seen resting on the drilling machine table and the timber baulk is there to support the front of the table, otherwise the pressure could break the casting. Three passes were needed to get the depth.
  2. Coupling Rods  
I prefer to use hot rolled steel (black bar) rather than cold drawn steel (bright) because it geneally doesn't go banana-shaped when one side is machined. I had to mill down some 1" x 1/2" for the coupling rods and this took quite a time. I used the waiting time to make the various bushes, pins and end caps but haven't bothered to describe the machining, it's all straightforward stuff. Once the rods had been machined to finished thickness and the sides cleaned up, the next job was to drill and ream the two holes for the phosphor bronze bushes. I've made these 10mm O/D rather than 3/8" and reamed the bore 8mm diameter.
I re-used a fixture that I made for the Britannia rods, a length of 1" square tube by 1/8" wall cleaned up all round. Two holes were drilled and tapped M5 at 6.7/8" spacing and offset to one side by about 1/8". I had already made a pair of bolting bushes with a 5.1mm diameter hole through when I made the PB bushes. The fixture was set in the vice with the ends supported on blocks and additional clamps used to dampen any ringing for when cutting beyond the bounds of the vice. Each rod was clamped on, clocked true and the shaping done with a 12mm end mill. With the "Y" axis set to the centreline of the bushes and the "X" zeroed half way between them, it was a simple matter to wind in, along, out then round to the other side and repeat using the same set of numbers. I also machined the upstand parts - I don't know what they are called - before removing from the fixture. The fixture was then flipped over and the flute machined using a 1/2" dia x 1/4" wide tee-slot cutter, taking a couple of 30 thou deep passes followed by a 5 thou cut in the climb-milling direction for a better finish.
To round the ends, I made a filing button and used the linisher and the Dremel although I could have set up the rotary table if I wanted to. The final job with these was to drill the oil reservoir in the tops of the rods using a 3mm PCB drill. All that is required now is to push the bushes in and drill through the oil holes with a tiny drill. DY's drawing is massively out-of-scale here, being drawn almost 1/8" shorter than actual. A timely lesson not to scale from drawings.
  3. Connecting Rods  
The con rods have been made in a similar way to the coupling rods, using a fixture to hold the work. After cleaning up the black bar to finished width and thickness, and with one end faced, they were loaded to a backstop and the hole for the gudgeon pin drilled and reamed 5/16" diameter. Using a pin to keep them aligned, the sides were reduced to 1/2" taking an equal amount off each side.
A pair of new holes were drilled and tapped M5 in the fixture and a top-hat bush made to fit the 5/16" reamed hole. The small end was held by an M5 cap screw through the bush and the big end was held by a clamp. The first operation done on the fixture were the two radii and a boring bar was used for this, doing one side first then flipping the workpiece over and doing the other side. The radius is a little undersize but I'm not getting anal about that. The tapered sides were made by setting the big end over by 3/32" at the root of the radius and four passes of twenty thou and one of ten made with a 12mm end mill.
The fixture was set on it's side and the thinning of the rods done next, taking 1/32" off each side. I changed to a 10mm end mill for this to get in tighter at the small end. For the second side a piece of brass packing was used behind the rod to stop it flexing. To complete, the top-hat bush was used as a filing button to round the ends and a pair of phosphor bronze bushes made and loctited into position. I will make the strap for the big-end brasses before drilling the two holes so these are finished for now.
  4. Big End Brasses  
Despite their name, they are often made from bronze and I have made the big-end brasses from the billets that I cut out from the main horns. After cleaning up all round and finishing the thickness at 3/8", two of the billets were reduced in width to exactly 9/16". These were then soft-soldered to the other two billets using silver-bearing solder. Once cooled, both sides were cleaned up to leave the thickness at 5/16". After milling the top and bottom to 1.1/32" across, the ends were squared up the easy way using a vice in a vice.
Then they were brought to finished size just using the main vice but because the two halves are not the same size, I had to make sure that I didn't take too much off one end, leaving too little for the other end. The bearing bore was machined on the lathe using the independent 4-jaw chuck to offset the centre but the picture I took was unusable. Back on the mill, the slots were machined next using a 1/4" diameter end mill. I once had a pair off brasses break at the join doing this sort of operation so, this time, I used a backstop to locate the work and then screwed up a front stop to trap the workpiece. Obviously, it only matters when the soldered join is perpendicular to the cut. Before separating the parts, I marked one pair with a single punched dot and the the other pair with two dots. Now they won't get mixed up or one half of a pair inverted. I will drill the oil holes once the bearing strap is made.
  5. Big End Straps  
To make these, I started with a couple of billets sawn from some 40mm x 10mm black bar. I'm not going to try and machine around the oil upstand, I will fit proper oil pots instead. They were cleaned up all round to finish at 1.7/9" x 1.13/32" x 1/4", making sure that the big-end brasses fitted nicely to the thickness.
The position of four pilot holes were worked out, these holes drilled 4mm diameter, and the centre cut out with a 4mm end mill. I used 25 thou depth-of-cut on each pass, winding round in a clockwise direction. The thin section at the left-hand end is left purely to provide support for the billet. After roughing out, a series of finishing passes were worked out to get the final size and shaping. The ends of the con rods are wider than the brasses and both these dimensions need to be as acurate as possible. I normally draw up a machining-steps list to ensure I don't mess up the workpiece, arrows showing where I'm going and the finishing dimension on the DRO. Here, Y0 is the centreline and X0 it the left-hand outer edge.
The hole for the stem of the oil pot was drilled next, followed by the outer form of the strap, reducing the width to 1.5/16" in a single pass of the cutter each side. Doing it this way gives the correct shape to the strap. All that remained prior to assembly was to remove the support section from the front with a hacksaw and clean up the inside faces. I've used the con rods to support the strap whilst milling.
The big-end brasses were filed to make a nice, sliding fit on the forks. I added centre-pops to the inside of each strap and on the ends of the con rods to keep the parts matched as two sets, then assembled each pair and drilled the cross-screws. Because they can't be seen on the finished loco, I've followed the drawing and used 1/8" diameter pins with 5BA threads on them but the prototype would probably have been proper cotters. After drilling the first hole, the pin was inserted prior to drilling the second hole. The pins were finished off with 6BA nuts overtapped with 5BA and a simple oil dashpot pressed into the top of the strap. Oil holes were then drilled 1.8mm diameter through both the big end and the small end bearings and the small end reamed to 1/4" diameter. The big-end bearings are already to size and need no further work.
  7. Crank Axle  
I made my crankshaft from multiple parts fitted together rather than machining from solid. There are four crank webs to make, the two outer ones being thinner than the two inner ones. I am making the later version because that is what Calbourne has now. Four pieces were cut from a section of 38mm x 8mm black bar. All four were cleaned up all round, albeit thirty thou overlength, with the two outer ones thinned to 1/4" and the 5/16" ones given a polish on the linisher. The holes were were put in next, working to a backstop, drilling each hole, then boring to near size before reaming with a 14mm reamer. The DRO allowed for very accurate positioning.
An old mandrel was re-used, turning the O/D to 14mm for a snug fit in the reamed holes. An M10 cap screw was used as the clamping bolt. The webs were loaded in turn and the diameter turned until cleaned up, then a further fifteen thou taken to bring to finished size.
The various journals are simple turned items but the 14mm diameter spigots needed to be pretty accurate and run very true so they were machined using the independant 4-jaw chuck.
The first parts to be fitted together were the webs and con rod journals. They were supposed to be a 2-thou interference fit but they were nearer a thou. To keep the axle journals square, they were pressed together using the mill vice. The piece of ground flat stock resting on the moving jaw was rested on top of the work and the quill lightly pressed down while the vice was tightened. Meanwhile, keyways were milled into the remaining journals and a 1/8" diameter hole drilled and reamed through each for later alignment but, because these are also only a light interference, they will be adjusted for radial position at assembly time. After final assembly, all the joints will be drilled and fitted with taper pins.
  9. Driving Axle  
Before I could commence the final build of the crank axle, I had to put the locking screws into the eccentrics. Once again, the fixture came in useful as a means of supporting them. I have drilled a 3.5mm diameter hole about 3/4" deep followed by drilling through 2.5mm and tapping M3 since I have a good amount of grub screws this size. The eccentric journal has to fit into the first web at 45 degrees and an alignment aid was set up on the mill; a pair of angle plates set square to the table and a pair of fences at 45 degrees, a tight fit to the webs. It's a bit Heath Robinson but more accurate than it looks, even though I'm using a carpenter's angle for the webs.
With a length of 1/8" diameter silver steel through the reamed hole in the keyway, it's a simple matter to get everything in alignment. Without this, it would have been far more difficult to set up. Before I pressed the shaft into the web, I replaced the support packing between the two webs to ensure that I didn't bend anything. The eccentrics were loaded to the journal and checked, rechecked and check again to make sure I had them in the correct orientation as it would be difficult to dismantle after the second crank is pressed on. The next picture shows the setup, much easier than trying to explain. The lower crank is clamped to the table and all packing is in place.
I've been pinning each joint as I went along but held off on this one for a moment. I wanted the cranks to be as accurate as possible so the vice was clocked true, the pinned crank held in the vice and the side face of the other one clocked out. I needed to ease it round a tiny bit and my large adjustable spanner gave me enough leverage. Afterwards, this joint was also pinned.
That just left the axlebox journals to be fitted and these were assembled, one at a time, in similar fashion to the earlier parts. Once again, the 1/8" diameter reamed hole, perpendicular to the keyway, allowed for accurate alignment. The coupling rod pins sit opposite the crank pins so the keyways were set towards the cranks. Early on, I decided to use Sellock pins instead of taper pins because it's a heck of a long way through for a taper reamer. These are 2.5mm diameter by 30mm long hard stainless pins, pressed in straight after drilling. After putting the keys in, I had to remove them again as they wouldn't fit through the bearings. A trial run with the bearings fitted into the horns and all is well. The axle rotates freely and, even at maximum depression, just misses the stretcher to the rear. I was half-expecting a collision here but it seems the draughtsman got something right on these
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