Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

DIY Homemade RAT ENGINE #2

It’s the school holidays down here in Oz and we also had a recent Long Weekend (yes we’re the land of the Long Weekend here) and myself and my 13 y.o Grandson made RAT ENGINE #2. (RAT ENGINE #1 we made some time ago).
I put out a call if anyone had some Mamod parts laying around and my friend Walter over Western Australia answered the call.
We had to make a new brass piston as the original was very worn.
RAT ENGINE #2 was made out of 2” copper plumbers’ pipe and 2” copper end caps. One of the end caps we turned down in the lathe so that it sat on the burner part of 2” copper pipe and that was silver brazed on.
The Mamod engine bracket was copper riveted on and then silver brazed on the inside of the pipe over the copper rivet and a touch of silver braze on the outside.

The ½” chimney stack we did something new, and silver brazed in some copper pipe cross sections (really made a difference to boil times).

Made up brass (yes only from brass) bushings for the safety valve and for the water level plug and tapped the safety valve bushing for a Jensen safety valve and the water level plug 6mm and turned up the water level plug out of some scrap brass.

We had some fun lighting a fire under the boiler with some gumtree cut up branches and leaves mixed in with a fire starter to test the boiler for leaks with only the safety valve installed.

The chimney stack is silver brazed into the firebox and we did that on our brick hearth….the rest of boiler was soft soldered together.
Also, silver brazed up the gas burner.
Turned the chimney cowl on the metal lathe from some scrap.
Brazed three (3) copper feet onto copper burner section of the boiler.
Needed to turn up some brass risers under the feet for the gas burner to work better.
There are some brass risers under the 5mm steel plate to help keep the heat off the routed timber plinth.
Bent and soft soldered in the K&S copper piping and made a copper bucket (silver soldered) for the condensate and soft soldered on a small copper spike on the copper pipe for it to swing on..
Cut the 5mm mild steel plate on the bandsaw and drilled and tapped it for the brass bolts.
Pickled the boiler in a strong Citric Acid solution.

All in all it was a GREAT time together, could it have been built better? Yes, but then my 13 y.o Grandson wouldn’t have had the fun and lessons of using all those tools and techniques. Instead of just watching, he was hands on building it.

We had some fun hours now the last couple of days steaming this together.


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That's GREAT Jim.

Hope he takes it to school as a demonstration project to talk to some classmates about it!

If they'd still allow such a thing these days?!?!

They have gas taps on their science desks at school so likely Daniel....but who knows schools are unfortunately pretty woke these days!

It was fun making this together.

That's grand...really Grand, what a wonderful time that must have been for you and your Grandson. Thanks for showing us (I miss this sort of thing)

Thanks Bruce....it truly was a terrific time mate and great memories made.

Thanks Gil, appreciated.