16mm scale "Linda"

[bambuko]

Thanks for the updates Trevor
Looking forward to more videos

One question BTW still not quite clear in my mind (and it is really a question about prototype rather than model) - is the securing of cylinders to the loco frame.
With very high cylinder line above the frames it seems very precarious to fix them just to the frame
unless there is also some fixing of cyliners to the smokebox

Perhaps TonyW with his inside knowledge of Ffestiniog will be able to enlighten us

[TonyW]

When first built the three locos had their cylinders attached to the frames by a single row of bolts with the upper part of the cylinders being bolted to the smokebox. Working on the FR soon showed up this weakness so Linda and Blanche had a front-end rebuild and now the bottom half of the smokebox is integral with the frames to support the cylinders properly. There is a lot more steel plate in the front end than there used to be!

[bambuko]

...bottom half of the smokebox is integral with the frames to support the cylinders properly. There is a lot more steel plate in the front end than there used to be!

Thank you Tony
I suspected something like this was the case, but it is not very clear in any of the photos in my collection

I know this goes beyond the modelling but I am interested in wider aspects of engineering and design

[TonyW]

Let me put it this way... if the top of the smokebox on Linda or Blanche needs to be removed it has to be cut off with a gas torch, and then welded back in place afterwards. The smokebox base is now a substantial structure and very firmly attached to the chassis. Hence we end up with views like this:


I wasn't around at the time, but this work *may* have happened in the early 1970s when the frames were extended for the pony truck. It certainly would have made sense to do it then.

[bambuko]

Both the info and attached photo are absolutely brilliant!
thank you Tony

Funny thing is, that I was thinking to myself, that is how I would strengthen things, but dismissed it...
a) because I had no photo evidence that this is what has happened
b) because it seemed silly idea

I guess the photo is from your private collection?

[Trevor Thompson]

I have remade the cab. Bit more effort than I intended to put into it but it is done.

I had to make a new spectacle plate, unsolder everything and then solder the new part in:

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Ready to try to run it again now!

Trevor

[Trevor Thompson]

Not had much to report on this until now. I mentioned in an earlier post that I was having trouble with blocked gas jets.

I am not sure whether it is an issue with dirty gas or particles of rubber from the flexible pipe carrying gas from the tender to the boiler which is causing this. I tend to suspect the latter!

I have now received 0.25mm drills and some woven brass mesh where the gaps between the wires are 0.25mm. Just right for a gas filter. I have drilled out the obstruction from the jet. After a couple of unsuccessful experiments I have come up with a technique for making a gas filter which seems to work. Firstly a small section of the mesh rolling awround a bit of rod:

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and the tubular mesh inserted into the end of the jet:

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I just screwed the jet back in place. The length of mesh tube should just be a mm or so longer than the hole in the jet carrier is long. I hope it will seal against the end!
So reassembled outside the boiler for testing:

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I have had it burning on and off during the day and it seems to have plenty of gas flowing. So reassembled into the loco I tried it out. Steam was raised and there is no sign of a blockage so far. However the servo controlling the reverser seems to have packed up - so something else to investigate.

Trevor

[Trevor Thompson]

It is a while since I wrote anything about this locomotive, really because it stopped working, and it has taken me quite a while to get it to go again. I have waited until I have solved the issues before saying anything!

So it was running fine along the track and I was about to take video when it stopped in mid flow. I worked out that the valve gear was not moving in keeping with the motion. This will illustrate why:

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The mechanism which transfers the valve motion is visible in the above photo. The cranks nearest the centre of the chassis were moving on the shaft - and losing motion. The loco would not go because the valves were hardly moving. I found some clockmakers tapered pins online which were much smaller than the 1/16 inch ones I had obtained from a model engineers supplier. The taper pin reamer I already had just happened to fit them. So the outside cranks were silver soldered to the shafts and the inner ones pinned. The benefit of the tapered pin is that a gentle hammer secures it so it won't fall out, and a tap from the other side makes it fall out. Of course as the taper is reamed into both shaft and crank it won't move either.

I was also concerned about excessive play in the valve eccentrics (they are really cams) which was caused by opening out the cam followers too much when I first built it. So I did what I should have done in the first place and made removable eccentric rods just like a car crankshaft:

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There they are at the top of the photo. Made from rod, bored and turned, parted off, flats milled for the boltheads, drilled and tapped and finally sawn in half. On reassembly they were mounted back in the 3 jaw chuck. I used the tailstock drill chuck to push it into the main chuck squarely. Then finally bore to just under size, and polish. I thought I was cunning to use the dremmel with a polishing head and polish, while the lathe and the dremmel were both rotating. It worked, nice fit smooth motion, no sticking.

Perhaps I should have mentioned it before, but the reason this took so long was that because of the way this loco is built, with the steam and exhaust pipework inside the smokebox, it is a nightmare to disassemble and put back together. When something is this awkward to assemble it makes it 10 times more difficult to assemble it well - as in with no steam leaks. The only way to really get at these cranks which were slipping was to take the whole loco to pieces.

[Trevor Thompson]

This photo shows the smokebox as it was - and I thought long and hard before I cut it into two parts! You will see why I did that in a moment.

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You can see the steam T pipe, the exhaust T and the holes in the smokebox where they pass through to the cylinders. As the loco is gas fired with a poker burner there is no need for the firebox to be airtight - in fact it needs not to be airtight. So cutting it won't affect the burning. I had also been finding the steam T to be difficult to get steam tight - so I silver soldered the T piece into the cross tube, and there is now only a threaded shaft/nut to make steam tight.

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Here is the after effect of the cutting. I used a metal cutting wheel in the dremmel - and managed to cut it quite accurately and neatly. It has been cut to allow the bottom part to hold the boiler down at the front, and to allow the steam fittings to be assembled out in the open, where I can get spanners to them. Of course it works as a locomotive with or without the smokebox so it was useful to leave it off for setting it up.

[Trevor Thompson]

Having changed the valve gear it took some time to set the throw on the mechanism to give the correct throw for the valves. I think part of the initial problem was that the valve mechanism was bouncing the valves off the ends of the valve chest. So I measured adjusted and measured again. I even made new parts slightly different in length to adjust the valve throw. Finally I adjusted the throw in the servo. So the locomotive reassembled for testing:

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Needless to say it does go again now, and I am making a few more modifications as I go along, to describe shortly.

Trevor

[bambuko]

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[Trevor Thompson]

While I was messing about with the cylinders I decided to add automatic cylinder drain cocks. I was a bit concerned about the hydraulic lock when starting up and everything was cold. It seemed to take a lot of force to get over "top dead centre". I wondered if that was causing the leaks on the various gaskets.

So while it was in bits I added an extra set of holes in the ends of the cylinders with drillings (0.8mm diameter) downwards leading to holes threaded 6BA. The 6BA is a size I have used before on the Garratt. You can see the edges of these holes, and one of the 6BA blanking plugs in the photo:

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This has 2 purposes:

I find it easier to set up the valve timing (for Stephenson and Walsharts valve gear) using pots of water. I have 2 plastic pipes with fittings on one end which are threaded 6BA. They screw into the holes for the drain cocks. They have brass weights threaded onto their free ends. One is screwed on in this photo:

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Continued below:

Trevor

[Trevor Thompson]

So to set or test the valve timing I replace the safety valve with a fitting which connects to the compressed air supply. Pressurise the boiler to a low pressure 15 or 20 psi will do.

With the loco on blocks so the wheels can be rotated, and the two pipes sitting in tubs of water, I can see when the valve allows air into each end of the cylinder. Here it is in forward gear mid stroke. You can see loads of bubbles in the left hand pot as the valve is fully open allowing air to push the piston backwards:

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Now look at the same thing when the piston is at the end of its stroke - just after "bottom dead centre". Ignore all the bubbles in the left hand pot (they are the result of all that air in the last photo and take a while to disperse). The right hand pot has just a couple of bubbles as the valve begins to open:

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With Stephenson valve gear one cam (eccentric?) controls forward gear and another controls reverse gear, so for two cylinders there are 4 cams. Each on can make the valve gear behave differently, depending on how accurately they are positioned on the axle. So potentially there are 4 cams to adjust, as well as the position of the each valve on its threaded shaft. This arrangement allows each of these settings to be investigated separately.

Anyway I have found that one the right hand side of the loco I can adjust the valve on its thread so that the valves open and close in the correct places in the cycle. So those two cams are OK. On the other side I cant quite get the same setting in ahead and astern. The adjustment is a half turn of the 10BA thread - and that is too course for getting the performance the same both ways. It is set correctly now in forward - and not quite so well in astern. However the loco runs both ways and forwards is uphill on my line - so that will do! I won't mess with the cam (I might make it worse).

On to the automatic drain valves next

Trevor

[Trevor Thompson]

Automatic drain valves - these are based on a sketch in the steam model locos group files - well they are my interpretation of them.

I have based them around some 3mm diameter nylon balls which I had in the components store. My working sketch is here:

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Each drain cock consists of 3 machined parts. Firstly a spigot which has that 6BA thread on its outside and has the other end reduced to fit into the next part. It has a hole through it.

The main component has a blind hole in it 2mm diameter to intersect with the first component, and then opened out to 3.5mm for about 4mm. it has an internal thread M4 in the last mm and a bit. This is the main body. It is silver soldered to the first component.

The last machined component is bit of hex rod with a 1.5mm hole in it and the M4 thread on its outside. That forms the lid which holds the ball in an has the sealing face on its inside (threaded) end.

Why M4 when everything else is BA? Its just that M4 is the only tap and die I had for about this size.

This is the final fitting in place:

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I know that it is normal for drain cocks to discharge steam to the front - but I found these needed to face backwards to let gravity help the ball to seal. Or at least they seem to seal more readily that way. Initially I had lots of trouble getting them to seal - steam everywhere! Things improved as I cleaned all of the swarf out and they eventually became clean. The slightest rubbish in there caused the ball to stick. Anyway they work - and there is very little steam escaping and I can see drips of water coming out when starting up from cold. Of course that hydraulic lock is a thing of the past.

I also modified the whistle and its valve.

Trevor

[Trevor Thompson]

I have made a whistle and whistle valve using the drawings in "Steam Trains in your Garden".

That steam valve is based around a tyre valve. I couldn't get it to seal reliably - so I designed my own parts to modify it. Working drawing again:

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It is basically a length of 2mm stainless rod (I know the drawing says 1.5mm but that is the nature of a working drawing - it changes as it develops!) The other dimensions are correct though.

So the original body from the book which has the steam pipe on its side, and a slot for the operating bar. In this case the pivot is underneath the fitting and the solenoid is under the footplate.

At the other end is a fitting to connect into the boiler, with a loose hole for the 2mm shaft and a recess at the other end to take a stainless spring. Another fitting connects these two parts together and has an external thread at each end, and a hole through it which is again a loose fit on the shaft. One end has a pocket drilled into it and a face for an O ring to sit on.

The shaft has a 2.8mm diameter "piston" silver soldered to it. Here is is ready to fit onto the loco:

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The fitting on the end os to connect to the air supply for testing.

and of course the whistle itself is from the same book.

Trevor

[Trevor Thompson]

The whistle is mounted in the cab upright. When I tested it on air it whistled - but on steam it sort of whistled to begin with and then just hissed.

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I eventually worked out that condensation might be sitting in the bottom of the whistle changing its effective length. A small hole in the side at end actually cured that. It now whistles really well!

Perhaps I should add that it seems important that the slot in the body lines up accurately with the end of the steam supply spigot.

[Trevor Thompson]

I have just been testing Linda on the railway. Here is a link to a short video of her hauling a train up a 1 in 60 slope. This isn't the limit of what she will cope with but I think it proves things .


https://www.dropbox.com/s/0pqbv95kgn8te ... 5.m4v?dl=0

You might notice that there is no water tank in the video. It is removed to modify it so it fits over the thicker insulation on the boiler.

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One thing I have been playing with is fuel. I have her steaming freely at the moment but it hasn't always been like that. My initial tests were with a gas container which ran out during lockdown. I then found propane from Screwfix - but that seemed to constantly block the jet. So I tried butane and the flame just died away as the gas tank got colder and colder. Of course the gas tank is in the tender and gets no heat from the boiler. I then tried a butane propane mix and that was a slight improvement - but not much. Of course there is no way of knowing how much propane is in the mixture. I bought some "extreme" gas (a mixture again) intended for winter camping, which claimed to work down to -27C. That was a big improvement - and is what I am currently using. I have also fitted a bigger jet - no 8 - which also seems to help with steam generation, but I am sure it increases the gas flow and therefor probably makes the tank cool down more quickly. However after a couple of runs up the slope I am still loosing gas pressure and therefor steam pressure. When I got to the point where the flame faded I let the loco cool down. When cool I tried to relight it and it lit straight away, with a healthy roar. There was definitely gas left in the tank. So I think I need pure propane to get the full potential out of this loco.

So I am on the hunt. Suggestions welcomed!

Trevor

[philipy]

Can't help with your gas issues, but I love that video.
That location is really photogenic, but I'd be a bit scared of a stray leaf or twig causing a derailment with that drop, though.

[Trevor Thompson]

Can't help with your gas issues, but I love that video.
That location is really photogenic, but I'd be a bit scared of a stray leaf or twig causing a derailment with that drop, though.

That drop has not proved a problem so far. I do check for obstructions on the line though. I started off with the railway raised because I thought it would be easier to operate manual controlled locomotives - but then I discovered radio control. The upper sections of the railway will be nearer to ground level - but I still like the prospect of being able to reach things without getting down on my knees.

Trevor

[GTB]

So I think I need pure propane to get the full potential out of this loco.

Forget about using Propane, unless you've designed the gas tank to work at the much higher pressures reached by straight Propane. Flexible hoses also won't take the higher pressures. Commercial model tanks are designed for the working pressure of Butane at normal temperatures, or mixtures that are fairly low in Propane. The Material Safety Data Sheet (MSDS) for a given brand of gas mixture will tell you the composition of what is being supplied.

The simplest way to use Butane in cold weather when the gas tank is remote from the cab, such as in the tender, is to locate it in a water bath filled with lukewarm water. Both my Shay and my Garratt have this arrangement and will run happily in very cold weather.

The maximum heat output of a gas burner is determined by the size of the jet and the pressure in the storage tank. Higher pressure and/or jet size result in higher gas flow and thus a higher combustion rate (and a higher consumption rate).

As a rough guide and averaged across a normal run, a standard Roundhouse burner will burn 0.6g/min of Butane and turn 5g/min of water into steam. I use those figures as the performance benchmark for my scratchbuilt locos.

Regards,
Graeme