THE COUPLING RODS

What with going away on holiday followed by a heatwave, which made the workshop too hot to work in, not a lot has been done this month. However, I have managed to complete the basic coupling rods. I always used the lathe for quartering in the past, but I'm delighted I stopped to make a jig this time. Once everything was assembled, with just a bare chassis including no bogey, so therefore quite light and minimum friction, the whole thing moved with the wheels rotating without any stiffness at any point. Much of this is due to the fact that I drilled all the pivot points on the mill using the DRO which is accurate to a tenth of a millimetre. Not forgetting that the axle boxes had to be accurately bored to the same standard.

The rods have only been roughed out with a coarse sanded finish, so I still have a lot of work to do to get a final polished effect. I also have to make the oil pots for the bearings. I did buy some flip-top ones but friends have scorned them and told me to make my own! I think they were a bit oversized anyway. I'm going to have to finish off the valve gear as much of that is still in a rough stage.
This second picture shows the connecting joint. I've made it as close to the full size design as I can from a vertical position. I still have to drill and pin them to secure the pivot pin.

Now that I have photos of the full sized engine, I've realized that the bogie wheels are not quite right. I think I'll have to have another go at turning them. This I'll do between centres. The photos show that the machining should be deeper, possibly to reduce weight, and also in two levels.

6 July 2006


I made several attempts at making oil pots to fit the coupling rods but they all looked wrong. Hindsight is a wonderful thing. What I should have done is take a magnifying glass to look more closely at the GA drawing. As can be seen from the photo of the leading wheel pivot, it is complicated so that the lines on the drawing are a confusing mass as everything is shown. Many of the lines are dotted, but I did work out what I should have done. Not wanting to make them all again, I set about altering them. It's taken over a week, partly due to the extreme heatwave and not being able to work in the workshop for very long. However, I am reasonably satisfied with the result, although the silver soldered joints do show if you look closely. They will be down low so unless somebody gets down on their hands and knees, they should go unnoticed.
The second picture shows the top of the pivot is brought up to a 'tower' which becomes the oil reservoir and is sealed with a bolt. I copied the original which had a washer extending beyond its sides. The brass bolts have a 1mm hole in to let air in as per full size. I'm told by those that know, that drivers used a piece of cane to fill the hole which let air in but kept dirt out. Note, I have now fitted the dummy bearing bolts. I'm pleased to say that the chassis pushed easily through one complete revolution of the wheels and no tight spots.
I'd almost finished milling one making sure that I was doing so in the right direction against the cutter, but having to start in a curve is always a danger and just as I was finishing it grabbed and the mill climbed all over it! So, fill in with the mig welder and start again. Worth its weight in gold.

I stripped the bogie so that I could turn the wheels between centres to look like the full size ones. Not sure I needed to have bothered as the difference is hardly noticeable; just a stepped area on the outer ring. Still, I did repaint everything which gave a good result.
I had a long discussion with my knowledgeable friend about the merits and de-merits of taper turning versus flat wheel treads. I haven't taper turned in the past because it makes making brake pads so much easier. However, it was pointed out that the original reason was to stop the wheels 'hunting' from side to side but that the full sized rails matched the taper whereas most model tracks don't. So where did that leave me? Well I ended up with a compromise; I put a taper on the bogie wheels and left the driving wheels as they are - flat.

I also decided to strip the whole chassis down as I have to rivet angle to the frames. This is double, one on the inside as well as one on the outside held by the same rivets. There is a tool box between the front part of the frames, hence the need for angle on the inside. Angle also has to be riveted to the buffer beam.
Once again not much done this month.

5 August 2006
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