2
Next job to be tackled was the front bogie and I decided to start from scratch and just used the wheel castings and the swing link centre. New frames were cut from 3/32" flat and I took the opportunity to make the bogie a bit more scale in appearance by altering the shape slightly and putting in some dummy bolts which in the full size version fastened the frames to the bogie centre. New hornblocks, axles and axleboxes were made and the wheels remachined to true them up. The treads were again coned to 2 degrees. This did leave the diameter of the wheels slightly smaller than the correct 1-5/8" but that shouldn't really matter. The whole was then reassembled with new swing links and pins. At the moment the springs are only temporary ones and will be replaced later. The dummy bolts have yet to be fitted as I can't find a decent photo of a full size front bogie! I am assuming they should be bolts but they could be rivets?
The new front bogie
As a way of a change I then took a look at the original smokebox and found it to be too large in diameter and about 1/2" too long. The door ring had been silver soldered into the smokebox tube which had been rolled from brass sheet. I cut off the front 1/4" of the tube complete with ring and also cut another 1/4" off the barrel end. The tube was then sawn along the original joint.A strip was removed to make the tube smaller in diameter and the joint resoldered with Easyflo. The tube was carefully made circular again by judicious use of a soft hammer and suitable former. The original smokebox ring was then chucked in the lathe and the outer diameter reduced to a tight fit in the smokebox tube. The front face was remachined to a new profile incorporating the raised lip around the smokebox door which is quite a prominent feature on the full size locos. A new adapter ring to take the boiler barrel was rolled up from some 1/8" brass strip, the joint silver soldered, and the ring turned to size. The ends of the smokebox tube were turned square in the lathe using wooden discs turned to fit inside the tube so that it could be held in the chuck. The smokebox door ring and adapter ring were pushed into the ends of the tube and silver soldered in place.
A new petticote pipe was also needed and feeling in a masochistic mood, I decided to turn a proper flared one from mild steel bar! This proved to quite a satisfying job actually with a lot of hand profiling. The straight part of the bore was given the correct diverging taper but probably this won't make the slightest difference to the draughting! The finished petticote pipe was then silver soldered into the smokebox tube ensuring it was exactly vertical.
Rebuilt smokebox with steel petticote pipe
Turning next to the smokebox saddle, I decided to completely remachine this as the finish was pretty rough and far too 'chunky' for my liking. I think really thick flanges on saddles where they bolt to the smokebox spoil the appearance of the loco. In any case, the radius of the saddle was now too large for the rebuilt smokebox so this had to be altered anyway.
To make it easy to hold the casting the base was soft soldered to a piece of 1/8" brass drilled with two holes so that it could be bolted to the vertical slide. The radius for the smokebox was then flycut with a cutter held in a boring bar. The underside of the flange was flycut with a tool mounted in a holder bolted to the lathe faceplate.
Flycutting the saddle
The sides and ends of the base were machined with an endmill leaving just the curved sides of the smokebox flange. I didn't fancy filing these so had to think of a way to machine them. Some time ago I had bought a set of cheap carbide router bits and decided to try using one of the ball end cutters with a 1/2" radius. This worked very well on the soft bronze casting and by taking several cuts at various positions of the saddle arrived at quite a good curve which just needed a little work with files and emery paper.
Using a carbide router bit to finish saddle sides
I decided to have a go at the coupling rods next to see how good the quartering of the wheels had been. These are machined from 3/16" x 1/2" mild steel flat and I thought it a good idea to drill the holes for the crankpin bushes first before marking out and machining the profile. Good job I did as I had a bit of trouble getting the holes spaced accurately by just measuring the axle centres. I tried making some eccentric bushes to correct the errors but I wasn't happy with the results. In the end I made an adjustable jig as described in Model Engineer on numerous occasions. This is just two pieces of steel drilled and reamed at the ends for the crankpins and a third piece joining these together with bolts. The bolt holes are oversize to allow adjustment of the distance between the holes. In use the jig is fitted with the crankpins on the centreline of the axles and the bolts tightened up. The jig is then removed and used to drill the holes in the embryo coupling rods. This method worked perfectly.
Coupling rod jig
The two embryo rods were bolted together and the top and bottom were milled in the vertical slide. The rounded ends were milled using a rotary table in the small milling machine.
Milling top and bottom edges of the rods
The rods need to be reduced in thickness between the bosses and this was done by bolting each rod in turn to a piece of angle bolted to the vertical slide and then milling to thickness. When one side had been machined the rod was turned over and a piece of packing was put under the machined part of the rod to prevent the rod flexing when milling the second side.
Jig for milling sides of rods
At this point I abandoned work on the coupling rods due to not having a suitable woodruff cutter for milling the flutes and went on to machining the cylinders. As you may have noticed I don't work in any particular order when building but machine components as and when I feel like it!
The original outside cylinders had been quite poorly machined and the valve ports were a right mess. The machining of the ports seems to be a real stumbling block for a lot of people, probably due to lack of rigidity in the machining setup and using blunt endmills. The ports on the Dairy Maid chassis and the Annie Boddie chassis are also badly cut. After some deliberation on possible ways to repair the damage I decided to get new castings for the cylinder blocks and the valves. The end covers and valve chests were ok to use again. Fortunately castings in this gauge are relatively cheap!
The cylinder blocks were set up in the 4 jaw with the casting bore running true and then bored out to slightly under 3/4". The bores will be finished by lapping with an aluminium lap to give a good surface finish for the piston O rings. The rear face of the block was also machined at the same setting to ensure it was square with the bore. The front face is not so critical and was done by just turning the block round in the chuck.
The cylinder was then bolted to an angle plate on the faceplate for machining the bolting face and valve chest face ensuring that the two were at right angles.
Set up for machining bolting face and valve chest face
To make cutting the ports easier I made a jig from a piece of 1/8"steel cut to the same size as the valve face. The ports were carefully marked out on the steel, drilled and then carefully filed to finished size. After drilling some holes to correspond to the valve chest mounting studs the plate was casehardened. In use the jig was bolted in position on the valve face and the ports chain drilled. They were then finished by milling with a suitable endmill. This method avoids having to mark out each set of ports seperately and the hardened steel jig prevents the endmill wandering and gives nice clean edges to the ports.
Valve port jig in use on middle cylinder
The steam passages were drilled by clamping the cylinder block to the vertical slide using packing on the bottom to angle the cylinder. A recess was then milled on the outside edge where the ports enter the cylinder.
Drilling the steam passages
Milling recess on the end of the cylinder
The middle cylinder was tackled in a similar fashion but this was a little more difficult due to the valve chest being at an angle to the cylinder bore. Once again the block was set up in the 4 jaw to machine the bore and the ends. The bolting face and valve face were machined by bolting the block to the angle plate bolted to the faceplate. The edges of the valve face were machined by clamping the block in a swivelling vertical slide rotated to the correct angle between the cylinder centre line and the valve spindle centre line. The ports were cut using the steel jig again.
All three bores were then lapped to a fine finish using an expanding aluminium lap and 600 grade Aloxite mixed with oil. I have loads of various grades Carborundum and Aloxite powders left over from my telescope making days when I used to grind my own mirrors.
Lapping a cylinder bore
The valve chest for the middle cylinder is in one piece with no seperate cover but is a fairly simple milling and turning job. The front and rear covers are again simple turning jobs, the only critical bit is machining the flat on the rear cover boss to take the single slidebar. This operation was left until I had made the crosshead and slidebar assembly so that it could be machined to the right height above the piston rod by trial and error. The piston was machined from a piece of aluminium bronze I happened to have and finish turned after fitting the piston rod to ensure it was truly concentric to the rod. The piston is fitted with a silicon O ring rather than packing, hence the reason for lapping the bores. A rough finish on the bore would quickly wear out an O ring.
The crosshead is machined from mild steel with a seperate top silver soldered on to make the rectangular bore for the flat slidebar. A separate oil cup made from brass is soldered to the top. The slide bar is machined from 1/8" gauge plate and left unhardened.
Complete middle cylinder assembly
After completing the middle cylinder my thoughts turned to incorporating some sort of cylinder drain cocks even though few 2 1/2" gauge locos have them fitted. Conventional drain cocks would be a bit flimsy in these sizes and very prone to getting knocked off. I was reading the design booklet for Toby and noticed the automatic drain cocks described therein. I reckoned it might be possible to use a similar design but fit them into the bottom of the cylinder rather than have a separate external housing. A 1/8" hole was drilled in the bottom of the cylinder wall to take the 3/32" stainless ball and a 1/16" hole drilled in the end of the bore to connect to the ball housing. The ball seats against a 1/16" reamed hole in the cylinder end cover. The principle behind these automatic cocks is that in the abscence of any water the ball is held against the seating by steam pressure. Any water in the cylinder causes turbulence in the ball chamber which prevents the ball seating until all the water is cleared. Whether my version will actually work remains to be seen!
Automatic drain cock fitted in the end of the cylinder