Welcome to
Steve's Britannia
5" gauge Britannia
Assembly & Alignment Drawing Errors 1. Mainframes 2. Pony Frames 3. Main Axles 4. Coupling Rods
5. Bogie 6. Pony Truck 7. Brakes, Sanding Gear 8. Cylinders9. Link Motion 10. Oil Pumps, Saddle
11. Smokebox 12. Boiler Detail 13. Boiler Fittings 14. Superheater, Ashpan 15. Valves, Pipework 17. Cab Fittings, Clothing
18. Cab & details 19. Footplates & details 21. Tender Frames, Axles 22. Tender WPU, Brakes 23. Tender Body 24. Tender Body, Filter
Drawing 3 - Main Axles and Wheels
1. Main Axles    
The axles are just a bit of simple turning. I have made mine from some 3/4" diameter EN8DM material that we always had in stock. 40-ton tensile so tough but nice to machine because of the slightly higher level of Manganese in it. First, I just roughed them out using the 3-jaw chuck and a back-stop, leaving about fifteen thou to come off the two journals but finishing them to length at this visit. After that, I set them up as shown to finish the diameters. A purist would probably use centres at both ends and a driving dog but my chuck runs true enough to grip one end and run the other in a live centre.
Having a shoulder for the chuck jaws to push on also helps when it comes to winding up the centre otherwise the work would probably creep backwards as the cut came on. I also changed over to a bit of HSS tooling here, partly because my rhomboid tool wouldn't fit anyway. It's also easier to take tiny cuts with HSS and we are talking a few tenths tolerance here. The pictures make the finish look rubbish but it's a trick of the light, they are actually very smooth. The last job that I needed to do on the axles was to mill the quartering keyways in the axles. This is not as per drawing but I have read many pages of discussion on the merits of either keys or Loctite to prevent the wheels from moving on the axle and decided that I prefer to use keys. It requires no fancy quartering jig to get them right first time, and they definitely will not move once pressed on. The easy way would be to mount the axles in a rotary table or dividing head on a milling machine.

However, I have neither but I did have a lump of 1" square bright mild steel bar and a length of this was used to make an indexing fixture, faced off in the lathe and a 3/4" hole drilled through it. I also added an M5 clamping grub screw about half-way along. Britannia has a right-hand lead so the fixture was marked accordingly and each axle loaded in turn to the fixture which was then held in the milling vice and the first keyway cut with a 1/8" slot drill. The fixture was then removed from the vice, up and over-ed and set back into the vice for the second keyway.

2. Axle Boxes    
The drawing suggests using the available gunmetal castings to make to main axle boxes but I have made mine from round mild steel billets. I would have used 2.1/4" dia material but I only had 2.1/8" at the time and that's why the corners are chamfered. The back face was first cleaned up on the lathe using the 3-jaw chuck and the billet was then reversed and all other turning ops completed in one go. Depths are quite important here because the distance from axle box face to bearing depth to axle shoulder, across the axle and back up the other side to the other axle box face has to fit the distance across the horns. Bearing diameter is, obviously, also important. Because of this, after drilling the through hole I chose to do all the bores and faces at one visit using a single boring bar and using the compound slide for varying the depths. I aimed for a light press fit on the bearing bore. Once all six were done, I marked out the finish position, plus about thirty thou, of one of the sides and then hacksawed the waste off and linished them reasonably flat. This made it easier to mark out the other three sides and rough those out as well. I chose to remove most of the waste with a hacksaw to save knocking the guts out of my tiny milling machine. To finsh machining the four sides, I just loaded them to the milling vice and flycut the top and bottom edges first, keeping a check on the wall thickness to make sure the bearing bore stayed central. Then the sides were done in a similar fashion although a little more care was taken here to get the size bang on. All that was left to do was to mark out all the various holes and then drill and tap as appropriate. I wont bother with the oil holes, though, because I am using sealed-for-life bearings.
3. Axle Box Covers    
The main job of the axle box covers is to control side-to-side movement of the axle where the outer edges bear against the gunmetal horns, although they are handy for holding the bearing firmly in the axle box. I have made the covers from billets sawn from 2.3/8" dia mild steel bar although gunmetal casting are available. I don't see the point since the horns are made of gunmetal and similar metals often fret if rubbed together. After deburring the edges and mounting them to soft jaws I first faced them off to clean up, followed by drilling and boring the 25/32" diameter axle clearance hole and clearing the bearing relief area still using the boring bar. I did all six like this before reversing them in a separate operation and facing the back, or outside as it will become, and forming the 1.1/8" diameter x 1/64" deep relief on that side. Finally, they all went back into the soft jaws for a third operation which was to turn the main axle box locating spigot which I made a thou or so smaller than the bearing diameter.
After that, they were sawn and milled an edge at a time to arrive at finished size, just holding vertically in a vice or, in my case, bolted to a faceplate and rotating round using a square to set the position. Accuracy is not important here, it's the axlebox with it's bearing depth that controls everything. Once they were all milled to size the only things left to do were to mark out and drill the bolt holes and then pair each one up with an axlebox, spot through and finally drill and tap the axleboxes. These are now ready for assembling with the bearings and axles although I will have to remember to make the pump eccentric for the centre axle first and slide it on before pressing the bearings on.
4. Driving and Coupled Wheels  
The driving and coupled wheels have the balance weights cast in and, consequently, are quite heavy but also out of balance at this stage. This meant that the lathe rocked quite a bit at higher rotational speeds. Since most of the turning was done at low speed, I decided that it wouldn't be worth trying to balance them with some bolt-on weights. First operation was to hold the flange diameter in the four-jaw independant chuck and try and get the best visual balance for the spokes and rim. The front was then faced and the tyre diameter turned about fifty thou oversize and a decent chamfer filed on the outer edge.
All subsequent operations were done in the three-jaw self-centreing chuck using home-made soft jaws because the chuck is a 5" diameter and the wheels are 6.9/16" at the major diameter. This method was chosen because it's quicker to load and get machining each op - soft jaws give good repeatability - and I don't have a large faceplate and didnt fancy spending all year clocking the wheels up at each operation. The jaw extensions are just bolted on with M5 cap screws but they will be perfectly OK for this application.
Once the jaws had been bored to suit the back was faced as a single operation, then the flange diameter turned and the axle hole drilled and bored to about fifty thou shy of finished size, all as separate operations. A ten thou depth of cut was used for all of the facing operations and each pass took about five minutes. Luckily, I have automatic feed in both axes so was able to use the waiting time to fettle out the flashing between the spokes with files and rotary burrs. I didn't count the number of separate operations but it must have been a dozen or so. When there were only two operations remaining, I reskimmend the jaws and also reduced the depth to seventy thou to give me room to form the angle on the flange with a form tool.
The last but one operation was to finish the axle hole and to size but I don't have a 9/16" reamer so I had to use a boring bar to get to final size and that brings it's own problem - measuring the bore! I used a spare axle and polished one of the journals down a thou to give me a Go/NoGo gauge. Once all the bores were done, I set the compound slide to two degrees and formed the two degree angle on the tyre diameter. However, just to be on the safe side, I clocked the bore and checked that the runout wasn't excessive before machining each wheel. It never went worse than half a thou.
To finish the driving and coupled wheels, they needed the holes for the crank pins made, the pins inserted and the keyways cut into the bore. The latter is not to drawing but is how i've chosen to quarter (and retain the setting of) the wheelsets. The position of the crank pins needs to be very accurate across all six wheels and I have, therefore, chosen to use a drill jig for this purpose. The jig is just a piece of 1.1/4" x 1/4" flat bar drilled and reamed 1/4" dia to take the locating peg at one end, drilled and reamed 1/8" dia at the crank-throw position and drilled and reamed to take another pin to locate between the spokes.
Using the jig, the crankpin holes were first drilled 1/8", then opened up to 23/64" with a drill that I had modified for cast iron, and finally reamed 3/8". The next job was to make the keyway bush with an alignment slot and a bush with a similar alignment slot to fit the crankpin holes. The two bushes were turned from some suitable mild steel and a 3/16" alignment slot milled into both. These need to be a good fit to the alignment bar to ensure that the keyway position is consistent across all six wheels. The keyways were cut using three passes of my home-made keyway broach (covered in a separate article HERE) just using my simple, lightweight drill press.
5. Crank Pins and Endcaps (see the Assembly page for further work)  
The crank pins and end caps were made from various offcuts of mild steel and are straightforward machining operations in the lathe. The most important part is getting the diameters accurate and concentric so the 3/8" diameters for press-fitting into the wheels and the bearing diameters were turned in a single operation prior to parting off. Each of the pins was then held in the 3-jaw self-centering chuck for any subsequent operations. There are two pairs and two individual pins that go to make up the set although they all have a common locating dia. The nearside rear crankpin differs from the offside because the speedometer bracket bolts to it.
6. Spring Brackets    
Because the spring brackets are difficult to hold I decided to make a mould to rest them in for the first milling operation. Some air-drying modelling clay was first placed in a matchbox then the casting, wrapped tightly in clingfilm, was pressed into it and levelled by eye. There are left-hand and right-hand parts so I then had to repeat the process for the opposite hand. These were then left to dry for a couple of days on the workshop windowsill. Once the moulds had gone nice and hard it was time to do a bit of machining.
First, each spring bracket was loaded into the respective mould with a tiny bit of foam underneath and then the whole lot was clamped gently onto the mill table, again lining up by eye. By taking small cuts I was able to mill the frame mounting face and register, the top edge and part of the side edges.This would be enough to enable subsequent operations to be done much more easily. Because I was able to machine the side edges, I could now hold the workpiece in a vice and machine the other side.
The reason for doing this, since they bolt to the inside of the mainframes, is to make it easier to mark out and drill the holes and to provide a good seat for the bolt heads or nuts. This is an example of where a set of soft vice jaws comes in handy. To machine the lower faces of the spring brackets I first drilled and tapped a bit of flat bar to match the bracket holes and then set this at 6 deg. on a small angle plate. I'm using a couple of angle gauge blocks but there are lots of other ways of setting the angle.
It was now a simple matter to just bolt the spring brackets on and flycut the face, reversing the fixture at the half-way stage for the other hand. The holes were spotted with a centre drill while the fixture was set on the mill and then the whole lot moved to the drilling machine and the holes drilled freehand. Finally, some of them need a little bit of extra work to allow mounting of the sanding gear and this was done using the same fixture just bolted vertical on the faceplate. These will be bolted on a bit later,
7. Spring Hangers    
I've had to make the main spring hangers different to drawing because I messed up on the axle boxes - I marked out the fixing holes from the wrong face and, consequently, the hanger pin would be out of position. I had no intention of scrapping the axle boxes after that amount of work so modified the spring hangers to suit. Rather than a circular base as per drawing I've made this part from a rectangle of 10swg mild steel plate and marked out the holes to suit. The rod part is 3/16" dia mild steel with a 2BA thread on each end but without the titty as there is no location point for it on the axle box. I will silver solder the two parts together a bit later on, I just need to find a way to hold the whole thing square while soldering.
8. Main Springs    
I have made the main springs from the castings and, although gunmetal ones are available, I was sent aluminium ones twenty-odd years ago. They are extremely poor quality and I will probably make proper leaf springs at some point in the future. I milled all round the buckle to clean the casting up and then milled the back of them. The spring holes were straightforward but the castings were set (by eye) in the vice at five degees to drill and tap the spring anchor points.
9. Brake Cylinder    
The drawing indicates that the steam brake cylinder is made from a bit of brass tube brazed onto a machined boss but i've made mine from solid using 1.1/2" diameter brass. Because of this, it won't matter what size I make the bore (within reason) as long as I machine the "O" ring groove to suit. I decided to turn the back end first, facing and turning the 1/2" spigot, drilling and tapping the steam entry port and skimming the O/D. I then loaded it to soft jaws to machine the opposite end. I went this way because the wall thickness of the cylinder is a bit thin and I didn't want to risk distorting it with any form of chuck pressure. First, the billet was faced to length, then drilled and bored to my chosen size of 0.994" and finally the O/D was turned to size. Then it was removed from the chuck, offered up to the brake cylinder bracket and the six bolt holes spotted through. These were then drilled on the drill press and tapped 6BA by hand.
The piston was made from 1" diameter brass skimmed to be a sliding fit in the bore of the cylinder with an "O" ring groove cut into the O/D to provide the seal, finishing this diameter at 0.724". The locating hole for the operating pin was made by drilling with a No.4 centre drill and plunging with a small high speed steel form tool made to suit which I have since lost, so can't show it here unfortunately. Finally, it was deburred and parted off
The few remaining items to complete the brake cylinder assembly were the pivot pin, the bell crank, operating pin, a couple of clevis pins and the return rod with spring. With regards to this set of drawings, anything which is specified as 1/8" dia with a 5BA thread is replaced by 3mm material with an M3 thread. The pivot pin is just a piece of unhardened 5/16" diameter silver steel, The operating pin was machined from a bit of 3/8" square mild steel, holding in my self-centring 4-jaw chuck to turn the 1/4" diameter and just filing the shape on the end. The fork was made the same way as I make all my forks, held vertically on the mill and machined through with the appropriate slot drill. The bell crank was made as two pieces and brazed together.
This is a picture of the whole assembly and here it is mounted between the frames. I have drilled and tapped a cross-hole in the bell crank to take an M3 cap screw and by locking the bell crank to the shaft I don't need to silver solder the bushes into the framework, just a dab of Loctite, so if they wear out (unlikely) I can just make a new pair and drop them in.
10. Screw Couplings    
The first thing I did was to turn up a simple former with a 5/16" diameter core size and bend four pieces of 1/8" dia stainless steel tube around it. I've found that this material takes tight bends without distortion if it is in a bending former. Using tube allows me to use 1/16" diameter pins to locate the eyes onto. The various components for the screw were made from 5/16" square mild steel, 1/4" square MS and other mild steel rounds as appropriate. There is quite a collection of parts to make two couplings. The only deviation I made from the drawing was to make the screw parts M4 rather than 5/32" x 40. Also, the lock collars are an interference fit allowing me to dispense with cross pins.
The eyes were made from 3/8" diameter mild steel and radii just filed on the outer edges prior to parting off. A 1.6mm dia hole was drilled through from the outside diameter to the centre hole, this being an interference with the 1/16" pins fitted in the ends of the coupling, and the assemblies pressed together in the vice. The whole assembly is press-fitted, no soldering, as it is a cosmetic item only. The last photo shows one mounted on the front draw-hook along with the vacuum pipe and the carriage heating pipe.
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