4 ms·

In the 80's my uncle, a trained mechanical engineer, tried to build a working scale small gauge steam locomotive at home for fun. He was a train geek. I reckon

In the 80's my uncle, a trained mechanical engineer, tried to build a working scale small gauge steam locomotive at home for fun. He was a train geek. I reckon it was maybe 1/16 scale or the like. He machined all parts on his Emco Unimat II, a 70's hobbyist convertible lathe. The final piece was beautiful. Ultimately the kettle couldn't build up enough steam because of tolerances of parts. He machined the resp. parts from scratch with more rigor. A year later, the 2nd version moved half a meter before it stopped for the same reasons. I remember his swearing and disappointment. But then he explained calmly to my cousin and me why he couldn't do any better w/o an investment into heavier, more precise and much more expensive tools. Too expensive for a hobbyist. Go figure.

adrianN 4y ago
I'd love to read a writeup on that project. Sounds fascinating.
- virtualritz 4y ago
  Me too. But unfortunately my uncle passed away two months ago.
foobarian 4y ago
I wonder if he was running into a cubed/squared scaling issue where scaling down the model made the operation impractical. Given same tolerances, a 16x larger dimension of the tank gives 16^3 more steam volume or at least 16^2 more heat flux which might make the gaps a lot more forgiving.
- bell-cot 4y ago
  Partly. But the weights to be move - the locomotive itself, any model cars, etc. - also weigh 1/(16^3) as much as the full-sized ones.
Damogran6 4y ago
That makes me wonder if I could do so with my 1966 South Bend...but then I think I'd probably finish the cylinder bore with a cheap Chinese Reamer, which is not something he would have probably wanted to purchase for a one off operation. (Think $300 for a cutting tool, vs one I can buy today for $25) You bore thecylinder to rough dimension, then use the reamer to set it to final tolerance.
- grogenaut 4y ago
  When making a real steam engine you use piston rings, you don't really machine to exact tolerance except where you're showing off how precise you are. The rings are consumable, they also flex since they're split rings (they're a C), which lets them expand as they wear. They're usually softer material or a slide compatible material with the cylinder walls. This makes them sacrificial and saves the much more expensive cylinder. You see them in literally every modern engine and I'm sure absurdly far back, even though they have better precision now. Your 1966 south bend is likely several orders of magnitude better than that emco, those things are more meant for wood, and imagine if you needed to align your spindle on your lathe every time you used it how inaccurate it'd be.

adrianN 4y ago

I'd love to read a writeup on that project. Sounds fascinating.

virtualritz 4y ago
Me too. But unfortunately my uncle passed away two months ago.

foobarian 4y ago

I wonder if he was running into a cubed/squared scaling issue where scaling down the model made the operation impractical. Given same tolerances, a 16x larger dimension of the tank gives 16^3 more steam volume or at least 16^2 more heat flux which might make the gaps a lot more forgiving.

bell-cot 4y ago
Partly. But the weights to be move - the locomotive itself, any model cars, etc. - also weigh 1/(16^3) as much as the full-sized ones.

Damogran6 4y ago

That makes me wonder if I could do so with my 1966 South Bend...but then I think I'd probably finish the cylinder bore with a cheap Chinese Reamer, which is not something he would have probably wanted to purchase for a one off operation. (Think $300 for a cutting tool, vs one I can buy today for $25) You bore thecylinder to rough dimension, then use the reamer to set it to final tolerance.

grogenaut 4y ago
When making a real steam engine you use piston rings, you don't really machine to exact tolerance except where you're showing off how precise you are. The rings are consumable, they also flex since they're split rings (they're a C), which lets them expand as they wear. They're usually softer material or a slide compatible material with the cylinder walls. This makes them sacrificial and saves the much more expensive cylinder. You see them in literally every modern engine and I'm sure absurdly far back, even though they have better precision now. Your 1966 south bend is likely several orders of magnitude better than that emco, those things are more meant for wood, and imagine if you needed to align your spindle on your lathe every time you used it how inaccurate it'd be.