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".

.

 

[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.

.

 

[Steamchick]

Fully trapezoidal shaped ports maximise steam input n exhaust, so gaining power compared to simple drilled round holes. So it depends if the model is powering something (typically a boat or generator) or will just sit doing nothing when running except idling....
K2

 

[salmonr]

Thank you all for replying, every day is a school day !

 

[Jasonb]

In these scales it is such a small difference you would not even notice it under power.

Take these two screen shots of the ports that I showed being machined above. To go from the mid way position

To fully overlap is only 2degrees of crank rotation,

To go from just opening to fully open only about 1 degree of crank rotation. The whole circular port face is 27mm dia, ports 2mm wide x 3mm long.

Seems to run OK and has reasonable power when given the thumb on the flywheel test

 

[salmonr]

Thanks Jason.

 

[salmonr]

I've nearly finished my first engine , I have copied for the most part Bob's engine. I machined the base out of solid , partly because I have no silver soldering facilities and the other reason is , I am considering making another cylinder unit to attach on the opposite side, mirror image ,and then move the flywheel in between the frame.I would have to do something with the shorter cylinder pivot and possibly use a spring washer. I had to remake the cylinder head as the internal thread that takes the gland nut went in wonky, due to a really cheap rubbish tap , and binded on the conrod when screwed in. [ I can here you all saying, you get what you pay for]. Although it's only a basic engine I was surprised how long it has taken me, but that's the beauty of being retired!

 

[GreenTwin]

That is just awesome.
Most impressive work !
So nice.
.

 

[salmonr]

That is just awesome.
Most impressive work !
So nice.
.

Thank you.