I'd actually made a start on the design of the brakes when I happened to come across a piece of plumbing which I thought was the ideal thing to make a better exhaust system. It's a piece which is a tight bend for plumbers to dodge round other pipes. Cutting it carefully at the correct angle took several goes. These were fitted into a larger tube cut to a point. The pointed part wrapped round to close the gap. Sounds easy, but proved difficult in that the threaded ends had to line up with the outlets on the cylinders, and the large tube had to be in the centre. Holding it together while silver soldering was tricky and one side fell out just as I was finishing. However, it's gone together and the upsweep is much better. I cleaned out the overlapping tubes inside the big one with a rotary file in my little Dremel. Being copper, it was easy to bend into alignment. The first photo shows that the large tube doesn't line up but it does in the fitted stage. I've left the big tube open as I haven't got round to designing the blast nozzle yet as I'm not sure of dimensions. I think it's a great improvement on my other one.

The brakes on this loco are steam operated as well as manual. This is my first attempt at a steam brake, my others have been manual on the loco relying on the vacuum brakes on the carriages for stopping power. I'm trying to keep everything to scale as far as possible but scaling the steam cylinder makes one which is far bigger than is necessary. So, it looks like being a massive tank with a small inner cylinder. All the rods etc. scale satisfactorily. The main brake shaft hangs from two brackets which are an interesting shape. There is no indication on the GA as to how they are attached, so I've used three bolts. No bearing is shown and as there is little movement, I haven't bothered to try and fit one.

The first component to make was the cylinder. I've tried to keep it reasonably to scale. I've used a lump of bronze which was cast with the hole down the centre. It's probably a bit too big a bore but should be OK. Photo shows all the bits. There's a drain hole in the cylinder and I've fitted a return spring which should be strong enough to take the pressure off after release. When assembled, there was the usual problem with the rod not being exactly central and so I had to work it free.
This next photo shows where it's mounted and how it will operate the brake shaft. I fabricated the drop link rather than carve one out of the solid mainly because I wanted it to look like the full sized one which is only a bare outline and no end view was shown so I had to guess how the sliding pin was fixed. The steam connection also incorporates a ball valve which allows for condensate to drain. Before fitting, I tried it out on air with excellent results. It's still a bit stiff through the end plate but this should ease with use letting the return spring work. This completes the lever system for the steam brake. One thing I'll need to think about and that's the driver's brake valve. The action on air was instantaneous, so a slow introduction of steam will be needed, otherwise the wheels will lock solid with a skidding halt!

2 November 2006

The GA drawing superimposes all the levers together making them appear to be on the one side whereas they are separate. But because of this, it is difficult to make out how the handbrake lever is constructed. I haven't been able to make mine exactly like the original because I've had to make allowances for the screw to pass through the bracket. To make it like the original, I would have had to support the screw at one end only, which I don't think would work.
There is another oddity too. There is no column; the top is supported by a bracket bolted to the rear bunker (yet to be made)and the base is not clear with a confusion of lines. However, the brake shaft actually slopes backwards in the drawing and I believe, allowing it to move to accommodate the screwing action. I've avoided this by making a short base which doesn't look out of place. Somewhere in the system I shall have to include a spring. The brakes can be screwed on or steam powered on but because of the slots, they can't be screwed off. The support of the bracket will be strengthened because the floor has to be fitted over the top.

Making six of everything takes a long time especially the brake blocks. I've made them from cast iron which I cut out from odd bits of old cast iron bar left over from pistons etc. It's surprising how much milling there is to make a rectangular block. Having milled the slots and drilled for the pin, there comes the problem of cutting the braking surface to match the curvature of the wheel. The picture shows my rather crude set-up and I was concerned as to whether the single bolt would be enough to hold them in place. But by taking very small cuts at slow feed and revs, I found it worked quite well. By opposing the blocks, the balance was quite good and at the end I measured the diameter inside and matched this to the wheels.

This next picture shows all the blocks and their pins. It also shows the fitting to the hanger and I've included the simple jig for drilling the holes in the pins so that they are identical as well as being central. The last picture shows the completed setup. It's difficult to show the inside 'workings', but the cross shafts are connected to the pull rods which in turn connect to the levers on the main brake shaft. To get everything set up in the right place I put everything in the brakes full-on position, I then ran a drop of Loctite 290 next to the levers. This is self seeking and when set, I took off the main shaft with its levers and brackets in place and completed drilling through each lever. Each had a 3mm pin fitted. Before fitting, I had drilled each bracket through one side only. The reason for not going right through is that when fitted to the shaft and then drilled, unless the drill is exactly vertical, it can wander and not be exactly in the middle of the exit hole.
Getting all the blocks to touch the wheels at the same time was quite a difficult adjustment. Unfortunately, I didn't have a left hand thread tap and die for 6mm. I could find a tap but not a die and any other thread meant a change of shaft diameter. So I had to manage with the same thread at both ends which meant dismantling to adjust each time. Still, I did get it to work. The brakes wind on very well but I've yet to work out how to fit a spring to let them off! Otherwise that's it for the brakes.

22 November 2006

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