Shed Matters 3

[Stanley]

Whilst I was having my second sleep the Design Committee were hard at work and when I woke they presented me with the answer to my eccentric problem. There is a reason I can't find an eccentric in the Westbury drawings.... it is that there never was an eccentric!
Instead there are two of these.....



This is a working model of a Scotch Yoke Eccentric. A mechanism for converting rotational to linear motion. I had accepted that this was the case for the drive from the steam cylinders to the pump but had assumed that in the case of the steam valves and the drive to the feed pump that these were conventional eccentrics. I was wrong, the drive is another version of the Scotch Yoke mechanism. The drive isn't from an eccentrically mounted crank pin as in the crank shaft but from an eccentric lobe on the inside of each flywheel.
I can see the way forwards now!

[plaques]

A quick call in on Stanley where he showed me the work in progress on the pump. A lot small unit than I had imagined made more difficult by making a solid double throw crank. The design committee's Scotch Yoke mechanism to to eccentric problem is spot on. A moving animation can be seen in the wiki link Scotch Yoke
Go for it Stanley you can do it.

[Stanley]

Thanks Ken! It was certainly a nice moment when I realised where I had gone wrong and what the solution is.
It's a lot easier to plan further progress now! Watch this space.....

[Stanley]

Now I have the drives from the flywheel to the valves and feed pump I know that I can address the drive between the cylinder block and the pump and fit them without jeopardising the fitting of the valve drivers. These parts are rusty so the first job is to clean them up before adjusting the distance between the Beams to fit the 1/4" crank pins. The reason this has to be adjusted is because I can't fit the die blocks recommended by the Westbury drawings because the shaft is chopped out of one piece of metal and not built up. In the full size pump the die blocks could be made in two halves but our build is too small.
I had to stop after an hour, the limiting factor was pain in my shoulder.... The sooner it mends the better!

[Stanley]

More work on getting the crankshaft yokes ready for fitting as this is the next job. As you can see the spacer bobbins were rusty as well as being too big. They all had to be adjusted and the bolts which fasten them checked for fit. The second image shows where I was at closing time, ready to do the final adjustments to the piston and pump rods before final fitting.

[Stanley]

One pic will do. This morning I had less than an hour but in that time I adjusted the piston and pump rods for length and cut the threaded ends back so that I could refinish the internal surfaces of the yokes ready for fitting. Now I need to prepare the cylinder and valve block for fitting.....

[Stanley]

The intention was to get into the work that needs to be done in order to fit the cylinder block to the pump assembly.
However, I realised there was one item hanging on from yesterday. One of the yokes had different bolts than the other. So I started by rectifying this. Easier said than done, it took me an hour to get to this point, largely because I dropped a tiny grub screw and spent almost half an hour in a fruitless search for it.....(That's the sort of thing you have to endure when you can't see!) However, eventually I got there but not without a lot of modification. Never mind, it's done now and once more I can start thinking about mounting the cylinder block....

[Stanley]

Later.... I went to have one more search and found the missing screw straight away.

[Stanley]

In my mind's eye this morning was making 6BA studs and fitting them but I soon realised it wasn't going to be like that. Whoever first tapped these holes had a very worn tap and the threads are undersize so I had to re-tap all the holes, 32 of them. Then screw in these long csk head screws and tighten them. What a good job I bought 100 of them. Now I'm ready for cutting them down and fitting the lids.....

[Stanley]

I nipped all the csk head screws back to length and then ground the ends so that they accepted a 6BA nut easily, then they went in the drawer with the the other 6BA stock. Then I opened the holes in the lids slightly to make the eventual fitting easier. The next job was to file the cut ends and fit a 6BA nut to each of them. After an hour I had done one side and started on the other but my shoulder was telling me I had done enough! Good progress.

[Stanley]

Dead simple this morning, fit the lids on the cylinder block and tighten them down. This is possible because I am not fitting the pistons. If anyone wants to do that in future good luck to them....
I got the top face done and the studs cut back to the nits. I started on the bottom face but as you can see I have a way to go next. I know where I will be going tomorrow....

[Stanley]

More quiet progress. The lids tightened down and the studs cut back to length then the studs for attaching the Cylinder block to the standards fitted, cut back to length and the screws cleaned up fitted with nuts and put in the stock. Next I attended to the Yokes, checked all the nuts and put them in place. Then all the nuts for the standards tightened down and the nuts replaced on the yokes. Not ready for fitting the cylinder block yet but getting very close!
A satisfying hour and a half......

[Stanley]

I wanted to free the shaft, it was too tight so I stripped the motion out and milled some more clearance into the standards. That cured the tightness but it remained to be seen whether it would still be free when all the rods were fitted in their glands and the assembly back together again. I'm please3d to say its a snug fit but free and so tomorrow I can go about tidying the studs and fasteners up before going forward to deal with the Scotch Yoke drives to the steam valves and the feed pump.

[Stanley]

Almost an hour and a half and you have to look carefully to see what I have done. First I made sure that, though snug, the crankshaft urns over freely. Then all the studs were cut back to the nuts and tidied with a small warding file. On the reverse side, the exhaust apertures from the cylinders were drilled and tapped and two short 1/4" stub pipes made and fitted. I finished by temporarily putting the flywheels on. Next I have to address the Scotch Yoke drives from the flywheel eccentrics to the steam valves and the feed pump. I said it was going to be complicated!

[Stanley]

Just one image this morning.... As I thought, the morning started with a trawl through the drawings to find clues and sizes for the two yokes I have to make to drive the steam valves and the feed pump. I found them eventually and in the pic you can see the fag packet drawing. Once I had done that I could go searching for the stock. You can see the results in the Teng magnetic bowl. Tomorrow I can start to refine the stock and do the machining needed. The bar of 1/4" silver steel is for the bobbins I have to make, not drawn yet but essential.

[Stanley]

Only one pic this morning for over an hour in the shed. Reducing these four pieces of flat bar to the size needed for the Scotch yokes. If you think that's a long time, try doing it! They will get refined further tomorrow.

[Stanley]

More work on the parts of the yokes. All drilled, bolted together and the ends squared in the mill. Then I started shaping the ends. I got one end done but time and my shoulder caught up with me. Never mind, there's always tomorrow!

[Stanley]

I finished shaping the ends o0f the elements of the Scotch Yokes and then drilled and tapped three of them. Then I made the rods for the steam valves and the feed pump and threaded them 5BA. Once fitted the interior surface of the bar had to be smoothed and polished. We are at the stage now where I need to make the bobbins that separate the bars. That's for tomorrow. This was a good hour. It's amazing how the elements grow if you just keep plugging away steadily at the tasks.

[Stanley]

Sorry for the hiatus Lads! I am OK but having a reaction to the flu and Covid jabs last week. Nothing serious but I am not taking any chances.....

[Whyperion]

A quick call in on Stanley where he showed me the work in progress on the pump. A lot small unit than I had imagined made more difficult by making a solid double throw crank. The design committee's Scotch Yoke mechanism to to eccentric problem is spot on. A moving animation can be seen in the wiki link Scotch Yoke
Go for it Stanley you can do it.

A few more coupling and motion transfer methods for Plaques to have a think on

[Stanley]

In case you're wondering what happened to the shed... I set off to go in there but changed my mind and went back to bed instead. I slept for another three hours! I don't think this is Covid lassitude, more likely to be old age!

[plaques]

A few more coupling and motion transfer methods for Plaques to have a think on

Fantastic. Always been a bit of a nerd on these exotic coupling mechanisms. In my youth I spent hours in the London science museum wondering how people thought of these machines. try Andreas Wannerstedt on YouTube.

[Stanley]

Feeling better this morning and so shed work is on again. The job this morning was to make the bobbins that are spacers for the elements of the two yokes for the valve rods and the feed pump plunger. They need final sizing tomorrow but essentially are ready for fitting.

[Stanley]

Just one pic to show where I was at the end of over an hour of fitting and adjusting. Lots of fits had to be eased. The bobbins had to be checked and resized to exactly .750". Finally lengths of rods had to be adjusted to allow fitting.
All of these have been done and you can turn the flywheels by hand and see how the yokes drive and are driven. I shall address some final finishing matters tomorrow but essentially I have gone as far with the pump as I want to. It's not a runner but if anyone wants to make it so they can strip it and do a rebuild.
If I could have seen this and turned the flywheel to see the yokes working I would have understood immediately! It's all been worth it just to get to that point!

[Stanley]

This morning was just titivating and tightening nuts. Two plugs made for the holes in the top steam cylinder covers. I can't find anything in the drawings for them so I just made plugs. The end result does what I intended it to, it shows the mechanism at work and particularly how the Scotch Yokes work. I shall make a stand for it now so it is stable.
I'm not sorry to see the back of this complicated little beast..... Especially as I was starting where someone had given up.