cylinders

The valve rod has a rather unusual set up. A support, which stands on the top of the top slide bar, is at an angle and has a cylinder through which the valve rod passes. This proved to be quite a job to make and had to be made to fit the side in question so that the rod slides easily in the cylinder. The two sides are not exactly the same, however carefully I made them, and as a result, each support is slightly different. The photo shows this up as I'd fabricated it from brass and bronze and then sprayed with primer. I've tried to copy the full size design, hence the extra support bar on the underside, which, from my point of view, does nothing useful. I now have to fix the support to the slide bar.

It's a very time consuming job fitting the piston and valve components together. Getting everything in line so that both the piston and the valve all slide without too much binding. The crosshead was again fabricated rather than go to the trouble of making a casting. The two difficult parts were making sure the thread lined up with the piston rod and that the brass slippers were in line with the slide bars as well as making sure the distance between matched the space between the slide bars. With hindsight, I think next time I'll construct the whole thing first and then mill the slide bar seats in the slippers.

While I was working on the design of this, one of the watchers of this site was kind enough to send me some photos he'd taken of the Hunslet which is about to be restored. As well as that, he put me onto an Australian website www.awm.gov.au where a completely restored one is on show with plenty of photographs showing most of the detail. The only problem is, I can now see all the things which I've had to guess at and are nothing like the full size. Most obvious, is the steam chest which has a most complicated casting on the top but no mention of it in the GA drawing. Fortunately, the whole cylinder unit is covered so it won't show, which is a good thing as it's a bit too late now. These two photos supplied by Phil Robinson, illustrate the complexity of the steam chest design.

As a result of the photos, I've spotted that the combination lever will foul the piston gland bolts and so I've had to change things in a similar way to the real thing. I machined off the side of the gland boss for clearance and repositioned the gland bolts. Having worked out the length of the con rod on CAD, I've made one so that I can run through a complete cycle to see if the piston is in the correct spot. After a bit of fiddling on thread lengths, I finally got there. One small problem in that the bottom of the con rod just touches the bottom slide bar. However, the wheels are not in the centre yet, as there isn't enough weight to compress the springs. When there is, this problem will hopefully disappear. The photo shows a temporary set up without the correct pins.

I was trying to get the expansion links water cut, but the minimum order was Ł100 so then I tried my usual laser cutter. Problem here was that I had to pay for the smallest sheet of gauge plate which put the price up to over Ł200! However, not all is lost; I bought a small piece from a model engineers supplier which will do the two - just. The laser cutter told me how to mount it on a separate sheet of steel, because as it was, it was too small to hold. As expected, the gauge plate is imperial and I didn't fancy cutting out the two links from 3/8" thick gauge plate. This is a bit thicker than I had intended, but it shouldn't make too much difference. The laser cutting leaves a rather rough finish so I've allowed spare on the inside for me to finish off.

The only way the two links could be cut from the piece by the laser, was to join them together at one end and then cut them afterwards. I was pleased to find that the cutting edge was greatly improved since the last job that was done and hardly any work was required to bring it to a mirror finish. The only problem was when I came to cut them in two. The hacksaw just bounced off. They were extremely hard. Somebody must have cooled the thing in water and so it became hardened. Somebody also removed the burr from the edge with a grinder and succeeded in touching the ground surface in a few places which spoiled the final finish. To get over the hardening, I heated to red heat and let them cool slowly. This worked well but of course, coloured the plate.

I've copied the full-sized pivot system which seems quite conventional, and pinned it to the link with a couple of 3mm pins.

It's taken me quite a time to get the dimensions for the valve gear correct. I wanted to make sure that what I made actually worked and was the same dimensions as the CAD drawing. As this was the first time with the design, I made nearly all the parts for one side. If I'd been sure I would have made both sides at once. So now I have the other side to look forward to!

It's surprising how long it takes to make some of the rods. I found that with one of them I didn't have any suitable steel. On top of that, had I got a piece I would have had to mill off great pieces. I made up one end with an offcut, ground the ends 45 degrees all round and then mig welded it to a suitable bar. Milling off the waste weld and a bit of re-touching with the welder and you'd never know. There doesn't seem to be a colour difference between the two steels. I'm not sure whether it was any quicker though. For the other end I just welded on a block so that I was sure to get accurate spacing between the pivots. I finished this end in the usual way after boring the pivot hole, rotating on a pivot against an end mill.

I assembled everything and disconnected the opposite side con rod to reduce friction and by turning the wheel by hand, I was able to go through the valve sequence to make sure dimensions were correct. Took me a while to get the eccentric rod the correct length and the same as in the CAD drawing. I hope I've now got it right although, I did have to manage without the reverser as I've still got this bit and the lifting links to make.
I must say I do like the design of the crank arm; a far better design than the Romulus one. I just copied the full size one. The clamp bolt worked well and when I've got it set right, I'll be able to drill and pin it. Much better than a cotter pin.

Although I don't appear to have made much progress this month, I have been busy. I've repeated last month's work and made all the components for the left side of the valve gear plus the weigh shaft and the lifting links.

One problem is to set the return crank at the correct angle and on the correct PCD. I found what I hope is an easy way of doing this. I turned two rods to a point, the diameter of which is the same as the two holes in the centre of the wheel and the centre of the return crank pivot. I could then measure the distance between the two points and do up the clamp bolt. I can now drill and pin. I haven't done this yet as I want to be absolutely sure before committing myself.

I've had to spend a bit of time working on the 'Romulant'. The pumps decided not to work. Getting to them was not easy and I had to use a hoist to lift one end. I discovered the disadvantage of having short stroke big bore versus long stroke small bore. The load on the big bore was far more and the pinning of the eccentrics was not strong enough to take the load and so they were revolving on the axle - and chewing it up! I also had complaints that my spark arrestor was not good enough so I've come up with another design. The ejector was only giving me 7" which was not enough to operate the vacuum brakes; that turned out to be a simple job by closing the gap between the jets. Not the best of running days.

These two pictures show all the parts placed in position. Theoretically it's just a question of bolting everything together, only I can't because there are a couple of jobs to do first. I'll have to sort out the pipe work for the inlet and exhaust ports and before the connecting rods can be fixed in place, the coupling rods have to be made and fitted. So I will take everything off first and then make the coupling rods. I'll also be able to paint various bits too. There is still a lot of work to do to bring the parts up to a finished condition. Another job before final fitting will be to make the piston rings as these cannot be fitted without removing the pistons from the cylinders. There will be some extras to make like the oil cups. I'm not sure how much will get done during the summer months.

THE VALVE GEAR

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