Plans call for brass, want to use aluminum instead

[vnks]

Hi stirling engine experts,

I would like to build Jonkman's Stirling 60 engine (http://www.machinistblog.com/downloads/ ... ing_60.pdf), which is originally made out of brass. However, this is my first machining project, and brass is really expensive, so I want to use aluminum instead, especially since I'm going to screw up lots of parts before I get them right. Would this engine work if machined out of aluminum? I'm planning to use brass for the flywheel, because it's much heavier, and aluminum for everything else, including the power piston.

Thanks!

[Ian S C]

vnks,not an expert, but a Stirling engine builder. Aluminium would be OK for most of the motor, I'd stick to brass for the power piston, and cylinder(it's only a little bit). If I was building it, i'd use cast iron for the piston, and a cast iron liner for an aluminium cylinder, this would reduce friction quite a bit.
Ian S C

[Ben]

I am looking for a cheaper alternative to brass for a flywheel, any ideas? (for a LTD engine)

[vnks]

Thanks Ian, I understand why I'd want brass for the power piston (more weight for the same volume), but why use it for the power cylinder as well? I would think that aluminum would actually be better since it has higher heat conductivity, so the cylinder will dissipate more heat in operation. Is there another reason I'm missing here?

[Ian S C]

Aluminium is not a good bearing metal, in most cases two different metals should be used, brass cylinder with a steel piston. Cast iron is the only exception to this rule, The little beam engine in my album has a cast iron piston in a cast iron liner with an aluminium finned cylinder, cylinder 3/8" bore.
You could make the fly wheel from steel, or my LTD motor, aluminium, with spokes made from bicycle spokes glued in place with super glue.
Ian S C

[CaptLink]

You could use aluminum for the fly wheel.The rim will need to be thicker or a steel ring could be pressed onto the aluminum spokes to add weight.The power piston needs a good fit to make power so thermal expansion is a consideration when choosing material.The displacement cylinder piston could be made from it but stainless steel would be better.

[Ian S C]

I generally use hot rolled mild steel to make fly wheels. People have used all sorts of things including wood, and plastic. If you use aluminium, increase the diameter by say a third to a half to counter the weight loss. It would be possable to use lead.
Ian S C