Re: Dake Engine Co. & Square Piston Engines
Posted by:
Peter Brow (IP Logged)
Date: January 10, 2003 08:59AM
<HTML>Hi Earl,
From what I've read, aluminum is not a good material for the steamy innards of a steam engine. It expands/contracts a lot at steam temps, corrodes, etc.. I considered something similar to what you mention, a minimal-machining version of this engine. At the time, I was thinking cold-rolled steel stock, which as Dave Gingery notes in his lathe book, comes in very close tolerances (I was amazed when miking some pieces I bought recently, within .001" of nominal size!). Best would be cast-iron stock, like the excellent stuff from McMaster-Carr, but I would expect foundry tolerances, and grinding or milling needed.
Yes, interesting idea for an engine project. The valving would have to be worked out. I wonder if they really did use occulted ports in the pistons, or if there was some kind of separate valve system in there?
Also, the pistons should probably be sized to give about the same displacement, for even running. This is a 3D geometry/math project that I didn't get too far into. Then there is sealing. Probably straight strips (steel key stock) with wavy phosphor-bronze wire springs beneath them, and overlapping stepped corner seals, to form segmented rectangular "rings". To minimize machining, these could go under removeable piston crowns. With some tricky detail design work, rolled factory flat edges could do all the bearing work, so nothing has to be milled. Countersunk machine screws or hucks to hold the plates together.
Run it with some lapping compound in there for a while, then disassemble, clean real good, pre-oil/graphite, and reassemble. Not recommended with soft metals! I was assisting in rebuild/replacement of a '65 'Cuda axle the other day. Mechanic, cleaning the stuck diff cover gasket off the pumpkin, sez git me the emery cloth. Owner, an old school mechanic, gives me all kinds of weird face signals, which I finally interpreted -- Uh, okay, can't find any emery cloth, guess we'll just have to scrape. I loaned him my knife. LOL. Owner didn't want emery in his bearings, gears, etc.. Then the guy drops U-joint bearing cap open-end-down in dirt ("ground cloth, what's that?"), & we send him for gasoline, newspaper, & grease, out come the wee rollers, & I get to wash, regrease, & re-position rollers by flashlight (& grease none too sticky, & this is 3AM in a dark Stephen King junkyard in the boonies with wolf-mix junkyard dogs circling us, & the disassembled car is our ride home, & 10 hrs of such screwups, whew). There's the difference between a grease monkey and a mechanic. Yeesh. Anyway ...
The journal in the inner piston could be an eccentric instead of a crank, for more bearing surface. This would probably run too hot for roller bearings, but grease or cylinder oil & prob an oil pump could do the job. Maybe 660 bronze bearing could be pressed in, but at that temperature?
Definitely a design challenge!
Peter
PS: why do they use roller bearings on the ends of U-joint tees? Outer races start to brinnell after a couple hundred miles! Lousy gas cars ...</HTML>