Next item on the agenda was the weighshaft assembly. The shaft itself is just a length of 3/16" dia. silver steel which runs in two PEEK bushes press fitted into the frames. Each end of the shaft carries a forked lifting lever which carries the pin which runs in the slot in the ends of the radius rods to raise and lower them and alter the cut-off. Just inside the left hand frame the shaft carries the reversing lever which connects to the reach rod. I had a few 'oh bother' moments when making the lifting levers and finished up having about three attempts at it. I had some 7mm square steel bar that came with a load of stuff I got from a workshop clearance which I used to make them. All went well until I came to slot the second one. The steel promptly blunted the slitting saw and just would not cut, yet I had drilled and reamed the holes with no problem. It turns out that the steel is either gauge plate or tool steel and was hard at just the very end! I then cocked up the next two due to the slitting saw wandering and not cutting a straight slot. By this time I was all set to abandon the job but fortunately the next attempt went ok. As it happens, one of the 'scrappers' was used to make the reversing lever so all was not lost! Both the lifting levers and the reversing lever are secured to the weighshaft with 1/16" taper pins.
The weighshaft, lifting levers and reversing lever
The last items in the weighshaft assemby are the pins that fit in the ends of the lifting levers. In most 2½" engines they are just simple pins which run directly in the radius rod slot. Larger locos tend to have a small die block which pivots on the pin similar to the die block in an expansion link. I had originally planned to fit a die block but decided instead to make a silver steel 'roller' which runs on the pin and should rotate when the radius rod moves backwards and forwards instead of sliding. This should decrease the amount of wear especially if the roller is hardened. The roller was a simple 1/8" length of 1/8" dia. silver steel drilled to a running fit on the pin. The pin itself was made the same as the other valve gear pins and drilled to take a 10BA securing bolt.
Radius rod with the pin and roller for the lifting link
There's not much more to do to the valve gear now before I can run the chassis on air and see what happens! I still have to make the two piston valves for the outside cylinders and the connecting link to drive the valve on the middle cylinder. I've got a piston valve blank left over from making the middle one and it shouldn't take long to knock the other one up. I haven't quite reached my target of running on air by the New Year but I'm not far off!
May I take this opportunity of wishing everybody who follows these 'ramblings' all the best for 2007. Let's hope it's a more peaceful year than the last one.
Now that all the fun and festivities are over for another year, time for another update.
The valve gear has been assembled with temporary eccentric rods made from steel strip (as these may need to be altered in length when the final valve setting is done) and the return cranks set to give the correct throw. The two outside piston valves were machined in exactly the same way as the inside one leaving them a slightly loose fit in the bores. As mentioned previously, final fitting will have to wait until the chassis can be run under steam at the normal operating temperature. The valves were fitted to the cylinders and all the valves roughly set 'by eye' using the tapped holes drilled into the steam chests. The holes were then temporarily blocked off with bolts.
The chassis was now in a position to be tried on compressed air. I made up an adapter to screw onto the steam inlet manifold which had the end turned down to accept the tyre inflator accessory for my compressor and set the compressor outlet pressure to about 20psi. After squirting some oil down the inlet manifold the compressor was connected and switched on. After a quick flick the wheels went around merrily despite the holes for the cylinder drain cocks being left unblocked and a few leaks from the valve setting holes etc. Big grin and a sigh of relief!! I had left the draincock holes open in the hope that any swarf etc. left in the cylinders would get blown out before doing any damage. After a bit I blocked the drain cock holes off with more bolts (as I hadn't yet made the proper items) and the chassis ran quite happily both forwards and backwards on about 15psi which seemed quite good considering the motion is still quite stiff. I think a lot of the friction comes from the O rings on the pistons and hopefully this will reduce when the bores are polished after a bit more running.
At this point I could not resist trying to rig up a steam supply and try out the chassis on steam. The only 'boiler' I had was an old pressure cooker that I use for making distilled water so I tried using that. Please note that the safety valves etc are still in place on the cooker so the maximum steam pressure obtainable is only 15psi. Under no circumstances would I recommend this to anyone else and definitely never try and increase the pressure by adding extra weights to the pressure regulating valve!!!
The connection to the boiler is via a length of silicon tubing (quite often used on small steam plants) and another adapter made to accept the end of that. After squirting more oil down the steam pipe (ordinary oil as I haven't any proper steam oil yet!) the 'boiler' was fired up (I lit the gas!) and after due time steam began to appear in the pipe. The motion was then turned over by hand to clear the inevitable oily condensation which came out of everywhere! I hadn't put any sealant on the bolts in the draincock holes or those blocking the valve chest holes so these acted as sort of drain cocks with water dribbling out of them. After a time the cylinders began to get up to steam temperature and, as expected, the valves started to tighten up as they expanded. I carried on until the motion became very stiff to turn and then disconnected the steam and let everything cool down. The valves were removed one by one and inspected. It was easy to tell those that had been binding as the surface of the valve was highly polished due to the friction. The culprits were mounted on the original mandrels in the lathe and a slight skim (about 2 thou) taken off the bobbins. The valves were then replaced in the cylinders, the timing reset, and steam raised again. This time the chassis definitely tried to run and after a lot of turning over by hand I managed to get it to run for a second or two with oily water and steam shooting out of the exhaust! At this point I decided to call it a day as there were so many leaks that it was impossible to keep up any sort of pressure. However things looked promising so I decided to have another go after I had made the proper drain cocks and sealed up the leaks.
The cylinder drain cocks are of the automatic type based on a design by Bob Thomas using a stainless ball in a horizontal chamber with a hole at one end that allows the water to escape. Turbulence in the chamber caused by water stops the ball from sealing off the hole. When all water has been driven out, steam pressure forces the ball onto it's seat and seals the outlet hole. I altered the original design to give an outline based on those fitted to full size locos such as the Horwich Crabs. These are fairly 'chunky' and allow a big enough body to contain the ball and it's chamber whilst keeping a scale size. The full size cocks are manually operated and contain a spring loaded relief valve as well. My version could be manually operated as well if the end is drilled for a pushrod to stop the ball seating of it's own accord.
Diagram of cylinder drain cocks
Before making all six drain cocks I knocked up a quick version just to make sure that the design would work. I fitted that to one of the cylinders and tried it under steam again. The cock worked as it should, letting out the condensate and then shutting off when it had all cleared. The ball seated perfectly and there was no leakage of steam. It was now ok to carry on and make the proper ones.
The bodies were fabricated from brass bar silver soldered together with the end cap pressed in and soft soldered after fitting the stainless ball. The balls were seated by the usual 'biff' with a rod and hammer. The two cocks for the middle cylinder do not have the dummy pressure relief valve on the bottom to give a bit more clearance for the front bogie
Finished drain cocks with a 1 pence coin for size
Drain cocks fitted to cylinders
The cocks need the threaded portion that screws into the cylinder reducing in length a little so that they will go not stick out so far. The little bosses on the underneath of the front part of the cocks are for fitting the copper drain pipes but I don't think I will be fitting those as they would be very vulnerable. I've just looked at my drawings for Don Young's Horwich Crab and actually both drain cocks should point in to the centre of the cylinder and not forwards as I've got them!
Next item was the cab reverser for the valve gear. After a bit of deliberation I decided to go for a vertical screw type reverser rather than the 'pole' type. I thought the screw sort would be less fiddly to make and the vertical type would probably be easier to operate than a horizontal one due to the limited room in the cab. Also the horizontal sort really needs a left hand thread for it to operate as per full size i.e. winding the handle clockwise puts the valve gear into forward gear. The vertical reverser works correctly with a normal right hand thread as the motion is reversed (no pun intended!) by the bell crank between the 'nut' and the reach rod.
The design is basically a copy of the one for Flying Scotsman and uses a 1/4" whitworth thread to give a reasonable number of turns from full forward to full reverse. I don't envisage running much in reverse anyway! I am not sure yet how to fit an indicator to show the cut-off that will be easy to see. Most full size locos with this type reverser have a remote indicator mounted on the boiler backhead. An easier way I think would be to simply mount a vertical slotted plate on the rear of the reverser and attach a pin to the nut which moves in the slot.
Vertical reverser fitted to chassis with temporary reach rod
Before conducting any more steam tests I thought it would be a good idea to fit a proper lubricator. The only really suitable place is between the frames behind the conjugated valve gear levers but even here space is a bit restricted. I looked at several types and eventually designed a twin cylinder pump based on the one for the Allchin traction engine. The normal oscillating cylinder type look a bit fiddly to make to me. The one described by Bill Hughes for the Allchin has a fixed cylinder with a spring loaded piston operated by a simple eccentric. The inlet port is a simple slot cut into the cylinder wall. Much easier to make in my opinion than the oscillating type. I decided to make a twin cylinder version to give a more constant oil supply as a single cylinder pump only delivers through a small part of it's cycle.
The lubricator went through several design changes during construction due to problems with the lack of space but I have eventually arrived at one that fits! The base of the pump is a piece of brass which contains the ball valves for the delivery side of the pumps with a cross hole to connect the two outputs together. The pump barrels are turned from bronze bar and silver soldered into the base. A slot in the base cut with a slitting saw forms the inlet ports for the pumps. The pump rams are 3/32" dia. silver steel with a mild steel disc silver soldered on top to bear on the eccentrics and accept the return springs.
The first design had a seperate outlet connection to one side of the valves with the pump assembly fitted into a rectangular tank made from 1/16" brass sheet silver solder together. This proved to be too wide and fouled the middle connecting rod unless the tank was mounted with the top sticking up above the frames when it would have fouled the bottom of the boiler! After a bit of thought I realised I could reduce the width of the pump base by combining the outlet with one of the delivery valves. By cutting a 'step' in the bottom of the tank it would then clear the connecting rod. The step was sealed with a piece of thin brass bent to an angle and soft soldered in. I could have just made a smaller tank I suppose but I didn't want to waste the one I had already made! Also the tank still has a fairly large capacity.
The eccentrics to operate the pump rams are turned from silver steel and silver soldered to the 1/8" silver steel shaft. The shaft runs in bronze bushes which are fitted from the outside of the tank and secured by thin nuts. Because the eccentrics are silver soldered to the shaft, the shaft has to be fitted in the tank before the bearings are put in place otherwise it would be impossible to get it in!
.......Lubricator partly assembled.......................................Slot in base that forms the inlet port
.......................Assembled lubricator body.........................Lubricator and eccentrics fitted to the final shape tank
Lubricator in position between the frames
All that the lubricator needs now is the drive assembly. Some time ago I came across a lubricator design described by LBSC back in 1939 that used springs rather than a ratchet assembly to convert the backwards and forwards motion of the operating lever to the required rotary motion. The idea is really very simple and works in a similar way to the one way needle roller clutches that many designs use nowadays. It seems such a simple idea and so easy to make that I decided to give it a go. The only problem I can forsee is failure of the springs with fatigue but we will see!
Two springs are needed with an internal diameter slightly less than the shaft they have to operate on and a 'tail' which can be clamped with a fixing screw. One is fitted on the shaft next to the lubricator body with the tail fastened to the body. If the shaft is turned in one direction the spring will try to 'unwind' itself on the shaft and the shaft will be free to rotate. In the other direction the spring will tighten itself on the shaft and grip it securely preventing any rotation. Thus the spring acts as a one way clutch and will only allow the shaft to rotate in one direction. The second spring is also mounted on the shaft but the tail is fastened to the operating lever of the lubricator. This second spring is wound such that it 'grips' the shaft in the opposite direction to the first spring. In one direction the lever will rotate the shaft and in the other direction will slip and the shaft will remain stationary.
I made the two springs from an old 28swg stainless guitar string ( I've got plenty of those!) but I think they will be too thin as LBSC suggests using 22swg. They will do to test the lubricator though. I can soon fit some more. I wound them on a length of 3/32" dia. bar which made them a nice fit on the 1/8" dia. lubricator shaft and made them 6 turns each.
First spring fitted to lubricator shaft
I've spent the last week finishing the lubricator drive and getting the chassis to run ok on steam. I'll post some more pics on the next update after I've cleaned all the steam oil off everything! It really is just like treacle and sticks to everything!
The drive for the lubricator is taken off one of the water pump eccentric straps by means of an extension arm and a wire link to the arm on the lubricator. The original springs made from the 28swg guitar string were too thin and resulted in a lot of 'backlash' before the drive took up so they were replaced with new ones made from 22 swg spring wire. These worked perfectly with no lost motion.The recent steam tests have shown that the spring drive for the lubricator works very well indeed, in fact the lubricator pumps far too much oil! The operating arm will have to be lengthened quite a bit to reduce the movement. This won't be a bad thing because it will mean that the operating rod from the pump eccentric can now go underneath the chassis where it will be easier to get at.
A lot of time has been spent getting the piston valves fitted correctly so that they do not seize up at steam temperature. The fit is very critical - too tight and they will seize, too loose and they allow steam to blow past them. I finished up making two new valves after taking too much off them! Fortunately it does not take long to make them. The important thing is to be able to fit them on a true running mandrel in the lathe so that they can be repeatably removed from the cylinder so that a slight skim can be taken off the diameter. This needed to be done several times. I eventually fitted them with the cylinders heated by a hot air gun to 140° C. The beauty of this is that each cylinder can be treated individually. When fitting the valves under steam it is difficult to tell which one is tight! The valves were left slightly tight at this temperature as I still do not know what temperature the cylinders will be running at under normal conditions.
When all three valves had been thus fitted the chassis was run under steam from the 'boiler' and it ran beautifully on about 15psi of steam and would have run quite happily all day I think. It seems to run well with the valve gear notched up to about 30% cut off when the exhaust just purrs so all seems ok. I let it run for about 15 minutes which was about the time taken for the lubricator to empty the oil tank! The automatic drain cocks work fine but some condensate still comes out of the exhaust. Mind you, the steam is very wet from the 'boiler' so I don't think this will be as bad when the cylinders are fed with proper superheated dry steam.
One thing that I have noticed and which confused me at first was the actual difference in the valve timing between full gear and mid gear. In mid gear the valves open to steam when the cranks are about 35 ° before top dead centre which is right for a lead of 0.01". However, when the valve gear is in full gear the valves open only slightly before TDC. When you read Martin Evans's book on valve gears (and articles by other writers) Walscheart's gear is said to give a constant lead at all cut offs. To me, this means that the valves open at the same point no matter what the cut off. This was obviously not the case and I began to think that there was something drastically wrong with Helen's valve gear! However, after studying the valve gear program by Charles Dockstader I realised that this is actually what happens and the lead does decrease from mid gear to full gear. When you think about it that's what you want to happen. In full gear the loco is only travelling slowly (i.e. starting off) so you do not want steam to enter the cylinder before top dead centre otherwise it will have a negative effect. As speed increases and the gear is notched up then the steam needs to be allowed into the cylinder slightly before tdc to get the best power output. Funny enough, a couple of days later I came across an article or letter by K N Harris covering just that topic! In this he said that some people had got it 'wrong' and the lead was only equal to the calculated value at mid gear when the only motion imparted to the valve is from the combination lever. When in full gear the motion of the valve is a sum of the motion of the combination lever and the radius rod and this does alter the lead. Nice to know I haven't made a cock up!!