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Building the Trevithick engine

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Brian Rupnow

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The Trevithick was a train engine built in or about 1805. It did prove that it could carry ten tons of freight as well as passengers for a short period of time, but was so heavy that it kept breaking the tracks. Other associated failures, and then finally a boiler explosion which killed four men was the end of the Trevithick. Similar engines were used for pumping stations for a few years after that, but it never really caught on as a commercial engine either. Richard Trevithick, the man who designed this engine died in poverty as an old man. The external gearing and an absolutely enormous flywheel make it an ideal hobby engine to build, because there is so much visual stuff happening when this engine runs. It has a very interesting steam admission valve, which sets directly in line with the cylinder body itself. I have attached a beautiful rendering that was sone as a 3D model by someone. Julius DeWall of New Zealand made absolutely marvelous detail drawings of this engine, however I don't plan on my engine being nearly as complex as the drawings Julius made, so I will more or less be developing this one "from scratch".---Brian
 

Brian Rupnow

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Here is a bit of information about the original inventor, and some insight into the story behind the engine. The most complex part of what was built was the steam valve which was built into an extended portion of the cylinder. I have no doubt about my ability to recreate the overall machine, but if I can't come up with some better info about the steam valve I may have to do something a bit different there.
 

Brian Rupnow

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As in all things, I have to determine what scale I want to build this engine at. That is going to be easy for me this time, because the largest gear I can cut on my milling machine is 108 teeth, which is 4.584" outer diameter. All other components will have to be scaled to accommodate this known part size.
 

Brian Rupnow

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So, based on ratio and proportion, and the fact that my largest gear is going to have 108 teeth, this lets me establish that the smaller gears at the drive wheels are going to be 50 teeth and the small drive gear is going to be a 36 tooth. All three of these gears are tied to the large gear by a function of adding the pitch diameters together and dividing by 2. I arbitrarily select the horizontal distance between gears, and so now they are fixed in position and can not be moved. No thought has been given to the width of the Trevithick yet, because that will be dependent on the diameter of the boiler.
 

Brian Rupnow

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Just as I was reaching a point where I didn't want to go any farther without more knowledge about the cylinder and valve, Julius from New Zealand has came thru with a bunch of drawings and saved me. Thank you Julius, from the far side of the world!!!

 

deeferdog

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As somebody who has just finished one of Julius's engines I can only add my thanks to yours, I think the man is a marvel. Cheers, Peter.
 
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Ken I

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Brian, Very cool - I've been thinking of building a Trevithick for years - so I'll be watching with interest.

Regards, Ken
 

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The Trevithick was a train engine built in or about 1805. It did prove that it could carry ten tons of freight as well as passengers for a short period of time, but was so heavy that it kept breaking the tracks. Other associated failures, and then finally a boiler explosion which killed four men was the end of the Trevithick. Similar engines were used for pumping stations for a few years after that, but it never really caught on as a commercial engine either. Richard Trevithick, the man who designed this engine died in poverty as an old man. The external gearing and an absolutely enormous flywheel make it an ideal hobby engine to build, because there is so much visual stuff happening when this engine runs. It has a very interesting steam admission valve, which sets directly in line with the cylinder body itself. I have attached a beautiful rendering that was sone as a 3D model by someone. Julius DeWall of New Zealand made absolutely marvelous detail drawings of this engine, however I don't plan on my engine being nearly as complex as the drawings Julius made, so I will more or less be developing this one "from scratch".---Brian
The Model Engineer magazine did a series of articles about his dredger engine which was a Modified version of the locomotive engine along with a set of free drawings Sept 87 - Oct 88
 

Charles Lamont

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... his dredger engine which was a Modified version of the locomotive engine ...
Other way round. As early as 23 Sept 1804 Trevithick writes a long letter from Coalbrookdale to his mentor Davies Giddy "which describes nearly fifty engines as built or building up & down the country." (Quote from the Dickinson & Titley biography) These were stationary engines for a whole variety of applications.
 

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Here is a bit of information about the original inventor, and some insight into the story behind the engine. The most complex part of what was built was the steam valve which was built into an extended portion of the cylinder. I have no doubt about my ability to recreate the overall machine, but if I can't come up with some better info about the steam valve I may have to do something a bit different there.
The Trevithick was a train engine built in or about 1805. It did prove that it could carry ten tons of freight as well as passengers for a short period of time, but was so heavy that it kept breaking the tracks. Other associated failures, and then finally a boiler explosion which killed four men was the end of the Trevithick. Similar engines were used for pumping stations for a few years after that, but it never really caught on as a commercial engine either. Richard Trevithick, the man who designed this engine died in poverty as an old man. The external gearing and an absolutely enormous flywheel make it an ideal hobby engine to build, because there is so much visual stuff happening when this engine runs. It has a very interesting steam admission valve, which sets directly in line with the cylinder body itself. I have attached a beautiful rendering that was sone as a 3D model by someone. Julius DeWall of New Zealand made absolutely marvelous detail drawings of this engine, however I don't plan on my engine being nearly as complex as the drawings Julius made, so I will more or less be developing this one "from scratch".---Brian
Brian:
I will watch this build with great interest. I purchased the drawing set from the museum in the UK. Right from the get-go my project was doomed. I couldn't seem to do anything right, so into the shoe box it went.

I will be very interested in the firebox you design. I tried to make an aluminum casting and was only semi successful. I was also having trouble understanding how the steam valve worked.

It looks like you're doing the project right so I'll keep watching and wish you all the best.

Bob
 

Brian Rupnow

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Bobcjohn--This engine I am building will run on compressed air, not steam. However, many of the parts and details will be of such a nature that they could be adapted to a steam powered engine.---Brian
 

Brian Rupnow

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I'm getting closer and closer to decision time on the steam cylinder and valve. Charles Lamont raises a valid point---I haven't found any Trevithick engine running the type of valve that Julius has drawings for. After much googling, I have found out that the Trevithick engine used a bell-crank lever to open and close a rotary 4-way valve. This means that the cylinder is basically just a plain cylinder, and the actual valving all happens in a separate block. It undoubtedly works, because there are a few recreated Trevithick engines running round using the rotary 4 way valve operated thru a Bell crank, as well as one completed model from Germany. I like the design by Julius, because there are no Bell cranks nor pivot points involved. Of course, the immediate question is has anybody built an engine using Julius' version of the valve, and how well did it work. Since I am not a stickler for authenticity, it seems I have three choices. I can use the same valve that Trevithick used, except I would be working from "scratch" and would have to develop the design for something a lot smaller in scale---OR--I can use what appears to be a much simpler cylinder/valve designed by Julius, ---OR---I can use a cylinder and valve body almost identical to that used on the Stephenson's Rocket, although if I do it ends up being a complete departure from what Trevithick did, but I know that it works.
 

Brian Rupnow

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So--Today Julius DeWall from New Zealand sent me drawings of his valve/cylinder combination. I couldn't get my cheesy little printer to print them for some reason, so they have been sent out to a commercial printer and will be ready for me to pick up tomorrow morning. I am going to model this valve/cylinder combination in 3D and see if it can be reduced in scale to work on my model engine.
 

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Brian:
Is it possible to make the wheel spacing the same as your last engine? I mentioned before that you should make a set of rollers the engines wheels can sit on so you can run them stationary to show them off (instead of across the floor). If you made this engine the same width you'd have another one for active display. It could sit on the shelf running.
 

Brian Rupnow

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I have spent today making a 3D model of Julius' valve/cylinder combination. I haven't spent any time yet determining how it's going to work, but at least I have all of the components modeled and mated. As modeled, this cylinder is only 18mm bore (about 11/16") x about 3 3/8" stroke. The piston rod is 4 mm diameter, (about 0.157") diameter. There are a bunch of ports which have to be added yet to the cylinder and a number of pipes to transfer air.
 
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Brian Rupnow

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I have been asked how the Trevithick compares size-wise to the Stephensons Rocket. It's roughly in the same ballpark, but far from being identical.
 

Brian Rupnow

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I have been moving the piston and steam valve around on my CAD system to see if everything makes sense. It seems to, with the exception of one cylinder port and I have asked Julius to check the position of the one hole in question. I have also asked again if anyone has actually built this configuration that he has drawn. Once I am completely happy with what Julius has sent me, I will start modifying it to give the bore and stroke that I need for my Trevithick model. Julius makes beautiful drawings. I have been badly spoiled by the practice in Canada of putting a detail of each part on it's own individual drawing. I've had to do some serious hunting on his drawings to find the parts I need to model.
 

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