Trevithick Overcrank Engine 1812

[JasonBModerator @jasonb]

While looking through some old MEs to see if I could find an engine for another member I came across a 4=part series by ET Westbury on building an engine by Trevithick that was use dfor threshing. stating in Vol 132 No 3301.

It is not a model that I have heard mention of it or seen any images of completed examples. The same applies for my Google searches for any reference material. So I’m wondering if any members can shed some light on the origins of the design, Westbury shows an engraving of what looks to be the boiler with the top of the cylinder poking out but no mention of where the image was found.

It could be an interesting one to build, I have a few ideas that vary from Westbury’s deviations but would really like an engraving or similar of a complete engine to go by. Google does throw up a threashing engine but that seems to be a horizontal boiler and most of the Science Museum images don’t show up.

Westbury’s GA

And the Engraving, which seems to have little if any taper to the boiler – what there is could just be perspective.

 

 

[Nigel Graham 2Participant @nigelgraham2]

Interesting!

That engraving shows no safety-valve – even allowing for it showing only the boiler anyway.

A dead-weight safety-valve would be more in keeping than the spring type Westbury specified – perhaps the orginal had none! No gauge-glass either, but boilers of that period had try-cocks.

Yor are probably right about the perspective effect. Rolling the barrel plates, in wrought-iron, might be thought not to have been very easy in Trevithick’s time even for a cylindrical drum, but they may have been able to roll tapers to sufficient repeatability. Early boilers were made in some odd shapes, often by hand-forging, so rolling plates for a slightly tapered barrel was likely relatively simple.

Would a Trevithick engine used a crank? I thought that was a later invention, by Mr. Watt.  What operated the “Distribution Cock”: some type of link motion or the engine’s human driver (as on the earliest pumping engines)?

Is the balance-weight on the right “side” of the flywheel rim? Shouldn’t it be opposite the crank?

…

The original would not have used very “strong steam”, and a model might well tick over nicely at only a few p.s.i. A bit more if connected to a threshing-drum – but what form did those take in Trevithick’s time? I expect like most of us, I am more familar with the big late-19C machines driven from a traction-engine.

When Ron Jarvis built his fine-scale Newcomen Atmospheric Engine he copied the original “weak” steam; about 2psi I think I recall correctly. To achieve this in a boiler the size and shape of a modest orange (and similarly dimpled to represent the correct hand-planishing!) he sealed its riveted seams from within, with ‘Araldite’ by a vacuum method; and “fired” it electrically, controlled by a thermocouple and associated electronics. Indeed, he would joke about this 18C engine with 20C microprocessor control.

 

I wonder if the engraving was made a long time after the engine had become disused and partially dismantled.

[JasonBModerator @jasonb]

Thanks for the interest Nigel. There is mention in the article about lack of safety valves, wooden beams etc and other deviations that Westbury made to give a more practical to make and run model.

One of the Members over on MEM forum has come up with a link that shows the engine much as Westbury describes with it’s brick base (he used steel) tapered boiler and no safety’s etc. The descrition is almost word for word the same. Downside is that it would seem to be an American Knock off of his horizontal boilered version. Need to decide which way to go with it now

[Nigel Graham 2]

On Nigel Graham 2 Said:

Would a Trevithick engine used a crank? I thought that was a later invention, by Mr. Watt.  What operated the “Distribution Cock”: some type of link motion or the engine’s human driver (as on the earliest pumping engines)?

 

As James Watt pre dates Richard Trevithick by about 35 years I think he would have known about  and used a crank.

Andy

[JasonBModerator @jasonb]

A bit more about the high pressure agricultural engines on Grace’s Guide

[SillyOldDufferModerator @sillyoldduffer]

I believe this chronology is correct:

• Thomas Newcomen (1664 – 1729).  Newcomen Engine 1712, a beam engine for pumping, not rotary.
• In 1780 James Pickard (with John Steed and Matthew Wasbrough), successfully added a crank to a Newcomen engine to get rotary motion and obtained a 12 year patent on the crank.  Controversial because cranks are age old.  Not known when or where the crank was invented, or by who – they’re ancient.
• James Watt (1736 – 1819) circumvented Pickard’s patent in 1781 with his Sun and Planet gear.
• Richard Trevithick (1771 – 1833) wouldn’t have been bothered much by the crank patent: he was only 21 when it expired.

Dave

[cogdobblerParticipant @cogdobbler]

Nigel: The flywheel balance weight is on the same side as the crankpin because it’s a single acting engine. The weight helped push the piston back down the cylinder on the exhaust stroke.

[Nigel Graham 2Participant @nigelgraham2]

Thankyou for that extra information, Dave. For some reason I thought Trevithick predated Watt.

Yesterday I found information that shows there is a lot more to the development of steam-power than often noted.

[JasonBModerator @jasonb]

Having given this a bit more thought over the last day or so and read through some of Trevithick’s correspondance in the Graces Guide link that I posted together with not having found the source of Westbury’s etching of the boiler I think I’m going to go with a “Trevithick Style” agricultural engine.

The sketch shows the basic form, more detail to be added

225mm flywheel in Trevithick’s usual 4 spoke and counterweight style
Forged crankshaft rather than Westbury’s more “machined” looking one.
Crank underslung from wooden beams rather than steel girders as the Hawkins one was underslung and I fancy having some wood in there
Some form of “cam” and follower rather than the eccentric of the American versions
Parallel sided boiler with integral firebox below as there is mention of the later in the correspondance.
I will put it on a stone/brick base surrounding 3 sides of the boiler as no details of how they may have looked if portable.

As for the boiler I’m inclined to go with a simple drum from copper 4″ dia x 75mm or so tall. My other single acting engines all work of 5psi or less so something like 30psi (2bar) pressure would seem enough, it is more getting the volume of steam for a short run of the fairly long stroke engine that I would be looking for rather than doing work.

Cosmetic outer skin for the boiler and firebox. This makes the rivited look non structural and I can have a dummy manhole cover for display. Take that off to fill and then fit a safety valve if I want to steam or an airline for playing. Most likely stick one of the camping gas burners under it, the same as I use for the hot air engines.

[Howard LewisParticipant @howardlewis46836]

Trevithick’s engine may have post dated Watt’s patent for the crank.

Watt’s patent hamstrung the Cornish engine for years, until it expired.

Although the 1824 engine at the Levant mine used a crank, so maybe they paid royalties.

(The engine only used four nuts, everything else was secured by tapered cotters!)

Howard

[Howard Lewis]

On Howard Lewis Said:

The engine only used four nuts, everything else was secured by tapered cotters!

I don’t think I will be going down that route!. Probably just the one to retain the big end bearing. Other fixings I will make square headed bolts and nuts for as I don’t like the look of the available off the shelf square metric offerings.

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