Stephenson’s Rocket

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Very impressive Bob. I always wanted to do the Rocket but I'm not sure I could achieve your level of workmanship. Really enjoying the build, please keep the pics coming.

Cheers, Peter
Thanks for your interest and kind comments. Peter, I still think of myself as a relative novice compared with some of the experts on here. My ambitions have always exceeded my abilities. If you look closely you will spot that the piece buried in wood is different from the final chimney. In other words I had two attempts before I was satisfied!

Started on the front springs.

I thought it would be a good idea to glue them all together to make them easier to assemble. But it wasn’t! I forgot that loctite needs both surfaces to be in good contact and they kept coming apart. Had to separate all the strips and clean off all the adhesive.
Anyway it worked in the end and here are all the bits prior to assembly:


And here are the parts mounted on the chassis:


Now I have to repeat the whole lot again for the rear springs

I have to take a short break from my workshop, so I am using the time to consider and draw the details which Julian has omitted from his "looking at" model. The biggest challenge is the valve gear, He gives no information about the eccentrics, the port sizes and throw of the valve. I can get a fair idea from Glithero's drawings but they are difficult to scale as they are all in isometric projection. So any help and suggestions would be most appreciated. I do know the size of the cylinder and the throw of the crankshaft, so I assume that would be the best starting point.

By the way, I did get more info from the NRM about these drawings Model of Rocket But they wanted £240 for proper digitised copies and that is a bit beyond my budget! They did say there is an ongoing project to digitise all their drawings which could be done in the next two years.

Hi Bob,
Not sure if this is of any use or how accurate it is but here is an illustration from the Museum of Science and Industry, Manchester UK. but given he provenance and age I suspect it to be pretty accurate, perhaps you could check some known dimensions as a proof. Here is an article written for the Museum.

Ho Bob,
There is also a rotatable (360°) model, which I just came across here, built from many scans of the original which was in the museum for quite a while. It can also be zoomed with the mouse as well and gives a good look at the workings. Remember that originally the valves on primitive engines would often be operated by the driver or his assistant. This shows a much lower rake angle for teh cylinders but again it was taken from an original. Also I just came across this on Wikipedia based of a full sized replica:

Thanks K2 and Terry. I found Bailey and Glithero's book has the best info and will try to work from that.

Got the rear springs made. Very fiddly cos there are 18 pieces in each side.


But this is what it looked like when assembled


Now I’m going to start on the cylinders and valve gear. The more I get into this project the more I worry about its complexities. I think I have sorted the valve ports thanks to the help from other members, but I have still to sort out the complicated eccentrics and reversing mechanism.
Steamchick had it right with the drawings from the Kensington Science Museum (SMG now)
In 1977 I was at the Wembley show and purchased a set of drawings from them.
Was told at the time that they had a model (1/8" scale) made in the late 1800's and they drew the plans in 1937
and they were available --I believe I paid 50 Pounds for the 10 drawings at that time .. but alas, I gave them to a friend years ago
I could be wrong, but at that scale the track gauge was either 6 15/16 or 7 1/16 " ..I remember it was a 1/16" off 7"
Nice plans and had the valve gear , but lots of /64" readings
Hi Rich. I have seen those drawings. Unfortunately the price has gone up to £240 for the set, which is a bit above my price range. They did say they are in the process of uploading all their drawings, and they should be freely available within 2 years !
Hi Rich.
Yes I should have said "available free", as I under stand it. I have actually bitten the bullet and ordered the sheet with the eccentrics and valve details. That was the part of the design I had difficulty following from Glithero's book. And yes I do have the Haynes manual as well. I like the way they call it the "Owners Manual"!
Got the cylinders made and associated bits to mount them on the boiler. The cylinders were made with the protrusion for the valve chest (not sure of the right name) all in one piece. The semi-circular part was done on the rotary table which was turned through a couple of degrees after each pass. Then smoothed off with a file. I bit the bullet and bought a print from the NRM of the sheet which covers the valve and eccentric mechanism. Still trawling through the layout in Solid Edge - watch this space.

Splashed out and bought the drawing from the NRM which covered the valve gear and eccentrics. The detail was perfect and legible. After much head scratching and reading Bailey and Glithero's book, I finally manged to work out how it all was put together. I wanted to animate the assembly in Solid Edge so I could be happy that it would indeed fit. So, working out how it worked and how on earth to use animation in Solid Edge took ages. But I cracked it in the end. For all Glithero's genius, he did not describe how it really worked (at least to my simple mind), so here is a description and drawing if anyone is interested:

The two eccentrics are keyed to a sliding collar which is free to rotate on the front axle. A sliding fork between them is used to engage one or the other dog clutch which are keyed to the front axle. Each eccentric drives an eccentric rod which is hinged to accommodate the transverse movement of the eccentrics. The eccentrics are connected via a bell crank which is keyed to the countershaft. The countershaft is actually in two pieces; an inner and an outer which is free to rotate on the inner. Two further keyed bell cranks drive the gab rods. Each one has a semi-circular groove which engage with the valve levers. The valve levers are keyed to the valve shaft, but it can be seen that we only want one at a time to be engaged. So there is a keep plate (not shown in the drawing) which can be slid over the semi-circular groove when the gab shaft is lifted clear. Yet another crank transmits the motion of the valve shaft to the valve rod and the slide valve. It must have been a challenge to change gear. The gab rod had to be disengaged from the valve shaft, the keeper slid across, the the other one engaged and the sliding fork moved the engage the other eccentric.

I think this is made more clear in the diagram and the animation. Some very fiddly bits to build. I've no chance of using keyways in a 1/16 dia shaft, so I'll have to think of an alternative means of fastening (any suggestion?). Oh, and I forgot to mention that the NRM drawings are in fractions (down to the nearest 1/128 inch) at 1/8 scale whereas mine is 1/12 scale in metric!


Eccentric and Valve Mechanism.jpg

Thanks Bob, Still trying to get my head around this. Great 3D scan of the original. Is the upper valve shaft not 2 piece? Just wondering why one upper valve levers would need to be disengaged for normal running. Now I'm afraid I am going to start showing my complete lack of knowledge when it comes to steam engines. Got me intrigued though.
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