Bob J's No.21 Steam Engine (drawings and STP files by Pat J)

[GreenTwin]

I made a crude steam engine for my 12th grade science project, with a lot of help from my dad.
It used a Briggs lawnmower piston, and was single-acting.

I wanted to build steam engines every since I ran across my dad's copy of "Audel's Power Plant Engineer's Guilde" back in the late 1960's.
I saw some fabulous steam engines in the Audel's book, and so I went around to the local hobby shop, where they sold Wilesco model steam engines, and asked "Where do I buy a real steam engine ?".
They said "Oh, they don't make those anymore".

So I have always wanted to make steam engines again, and if possible, make full sized engines, cast in gray iron like the original engines.
Its not really a hobby for me, but rather a lifelong obsession with recreating something that most assume has vanished forever.
It bothers me when someone says "You can't get those anymore, and you won't be able to make one yourself either".

My philosophy is "If it was made at one time, then it can be made again in the same or improved way".

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[Steamchick]

I like your Dad. I had a Dad like that too. I failed to reach the standards my Dad achieved, but that is mostly a skills thing. He did it for 70 years. I flew a desk for 45 years and only did modelling n stuff for 30 years.. with a "bull at the gate" attitude that was never best for making good models. I have calmed down a bit in recent years, so hope to make good models soon.
K2

 

[salmonr]

The engine is coming along fine , thanks for all your help. Being new to steam engines , I was wondering what the relevance was of the shape of the ports.I can replicate the shape of the port on the drawings , but it's a lot of work as apposed to say a parallel slot. I will no doubt copy the drawing , just wondering what the advantages are of the tapered ports.

 

[Jasonb]

On a model like that just round holes would do or you can mill radial slots which as you say are a lot simpler.

 

[GreenTwin]

I had forgotten that there were tapered ports on this engine.
I think those come from a literal rotation of the cylinder, mapping out the path its port would take.
That is how the full sized engines were built, so that the entire port opens and closes all at once.

As Jason mentions, radial slots will work find, and that would probably be how I would mill the ports if I were doing it, given how small the ports are, and how tricky it would be to get then tapered.
The engine will run fine without the tapered port.
For a full sized engine, you would want to taper the port to prevent wire drawing, which is where a small part of the port opens before the rest of the port.

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