johnsmachines

machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment. I read every comment and respond to most.

Tag: London Science Museum

London Museum of Science Revisited

I am back in oz as of a few hours ago.  Freezing and wet.  Was 26c in London today.

On my last afternoon in London I had a few hours spare.  So I caught the tube to have a final farewell to the Trevithick dredger engine and to reshoot some photos which I had messed up at my visit 3 weeks earlier.

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Trevithick dredger engine in the LSM.

…and I spent a very pleasant hour photographing the engines in the Energy Hall again.

And on wandering further into the building I discovered that on the previous visit I had totally missed about 2/3 of the entire museum, including the model of the Trevithick road vehicle which had been made as a concept model by Trevithick’s brother in law, a clock maker.

Unfortunately it was bottom lit and behind glass, so very difficult to get good photos.

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From above

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From the side.

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The model is more akin to his road vehicle “Puffing Devil” than the rail locomotive.

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Quite modern looking lathe by Richard Roberts 1807.  With lead screw and outboard gears for threading.

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Beam engine designed by James Watt 1797.

 

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Model of a steam powered workshop, with many tiny exquisitely modelled lathes, shapers, presses, saws, and a steam engine.  Those lathes are about 3″ long.

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And a 1:12 model of a pressure gauge of James Watt, 1794.  60 years before the invention of the Bourdon tube.

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And this one amused me.  It is a 1987 Colchester CNC lathe, with Fanuc controller.  It is 2 years newer than my Boxford CNC lathe.

This really was the finale of my adventures in the UK.

 

Trevithick Dredger Engine at The London Science Museum

I landed at Heathrow at 6am, dropped my bags at the BNB, then caught 2 buses to the Science Museum.  Not jet lagged, but on a high, to see the only intact Trevithick Dredger Engine known to exist.

The room which houses the Trevithick, also contains 4 large beam engines, a Parson’s turbine (of “Turbinia” fame), and a very large 2 cylinder compound.

Disconcertingly, the first atmospheric beam engine, with wooden beam, was partly obscured by a souvenir stall and racks of clothes for sale.  WTF!   Don’t they realise the historical importance and rarity of these engines.  And 3 further moans, to get them out of the way.   The descriptive labels on all items had minimal information.  Nothing like dimensions, power, etc.  The attendants knew virtually nothing about the engines.  And often, items were behind glass or perspex which was reflective, and prevented good visualisation or photography.   To be fair entrance was free, but to get past the entrance desk it seemed pretty clear that a “donation” of 5 pounds was expected, (which I was happy to contribute).   Those complaints aside, I have to say that the collections were fabulous.

I could see the Trevithick at the far end of the room, so to curb my mounting excitement, I forced myself to not rush up to it, but to try to look at every exhibit on the way.

Eventually I was there and it was there in front of me.

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It was one of the smallest engines in the room (The “Energy” hall).  The older beam engines were many times larger, but that was a major reason this engine was so successful..  more power, lighter, smaller, and several times more efficient at converting coal to rotative motion.  No one could tell me why there is a huge divot in the cast end of the boiler.

The con rods, stands, standard cross tie, and chimney are not original, but were added when the engine was restored in ~1875.  But that is now part of its history.

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From that side it was apparent that the main shaft was square over its entire length, something not previously known to me.

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The boiler feed pump was relatively tiny.  I do not know if it is original.

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The firebox has been re-sleeved.  The chimney mount is part of the end plate casting.  And I think that I got most of these items pretty close to right on my model.  Does anyone know what the incomplete flange at 5 0’clock would have been for?

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Note the odd bolt pattern around the inspection hatch.  I got that wrong.  My change to the oblique slide rod stay angle brackets was correct.

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safety valve weight is adjustable.

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Water preheater pipe detail.  Aren’t the square nuts great!

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The throttle restraints are curved, and have fixed position holes for pins.

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Boiler feed tank.  Cast iron.

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Engine supports appear to be cast integrally with the boiler.

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Flywheel hub

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Flywheel spoke detail.  Likely original.

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Chimney mount detail

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Finally (although I do have more photos), a nice view from above.  I do like the crosshead shape.  I wonder if it is original.  Remnants of another Trevithick dredger engine  not currently on display, reveal a wooden crosshead beam.

So there you are.  Fascinating to me.  Interesting enough I hope to you.  I could see no evidence of wooden lagging at all, but i still intend to install some on my model to slightly improve its efficiency.

i have heaps more photos of other exhibits which I may post later.

 

 

Trevithick Dredger Engine – what was the original design? -2

Further reading and exploring web sites, email to London Science Museum (LSM), asking opinions of boiler experts.  Even considering a quick trip to London. (from Oz).

What I have learned is interesting.

Richard Trevithick did not manufacture any of the several hundred of his high-pressure engines.  The ideas and designs were his, but the engines were manufactured in different sites and by different makers.  The designs changed with time and as new ideas presented themselves to the brilliant mind of Trevithick.  And each manufacturer put their own stamp on the designs.

For example, look at the following pictures of the boiler flat end plate.  One is in two pieces, riveted together.  The other is a casting, and the flanges for the inspection hatch and the chimney, and probably the blowdown valve orifice, are almost certainly part of the end plate casting.  The firebox looks newish, slipped inside the original end plate casting.  I guess that the original firebox had burnt out, but was probably similarly held in place.   If any Brit readers can pop into the LSM and check this out I would be very grateful.

Trevithick boiler shell

B002617 hi res

The model which I am making, and dithering over the end plate design, is based on the reconstructed engine in the London Science Museum.  I intend to remove the aspects which are obviously Victorian in origin, and replace those with parts that I think will be closer to the Trevithick era designs.

Unfortunately, I have already made some of those parts, so my redesign is a bit compromised, unless I scrap them.  Which I do not intend to do.

So this is my redesign of the end plate.  Not quite LSM.  And not quite Tubal Cain/deWaal Not quite, but will have to be close enough.  The red lines are already machined so I am stuck with them.  14 drilled and tapped holes have been filled.  The bronze inspection hatch/plug has been made, but with less standout than shown in the lateral view.

end plate

As an aside, while pondering the end plate, I have made a start on the engine itself.  The cylinder has been roughed out, and will be finished in my next workshop session.  Cain specified brass, deWaal specified bronze.  So I have compromised, and have used an unknown brass/bronze/copperish lump of workshop metal.  It is certainly hard, as assessed by filing.  Photo next post.