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The Artful Bodger might, might, make a little engine!

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John Hill:
So I am thinking of a little engine, I suppose one really should build a little oscillator engine as a first engine but the Artful Bodger is never one to follow custom and common sense.

I am thinking of a steam (air actually) engine with piston ported valving using a technique someone must have used before but I have never seen described.  What I have in mind is a piston with a very deep skirt on the top side that will act as a sleeve valve.  As the piston moves it will open input and exhaust ports.  The feature that will (might?) make it interesting is that the piston will both reciprocate (that is, move back and forth) and will also partly rotate about its axis,  sort of twisting one way then the other about 70 degrees or so.  The rotation of the piston will be caused by having the crank pin inclined in relation to the crankshaft axis and the connecting rod will have Hook's joints at each end.  Having the piston partially rotate in this way means that a point on the surface of the piston will prescribe an eliptical path and I can drill the ports to give a suitable duration of input and exhaust openings.

So far I have made a cylinder and started to turn the piston though that is quite difficult requiring a small boreing bar that I dont dont have as yet,  I need to turn a fairly deep 22mm into the head of the piston and that will form the sleeve.

So far I am thinking of steel for piston cylinder etc.

There is a long way to go on this one and I am currently travelling on the Mainland for a couple of weeks.

Cheers

John
a.k.a The Artful Bodger

sbwhart:
Hi John

That sounds an interesting engine  :headbang:

You could try making the small boring bar out of some silver steel (drill rod)

Good luck with the project

Stew

NickG:
Hi John,

Don't know if you're aware but there is already a recognised design of a slight variation on that theme. I know you said you're going to come up with your own design but it may help?

http://www.homemodelenginemachinist.com/index.php?topic=3382.0

http://www.workbench-miniatures.com/opv.htm

John Hill:
Thanks Nick, that is a good explanation of something I had heard about but not previously seen in such detail.

Although the motion of the pistion is similar that explanation states the valving is symetrical and the engine will run equally well in each direction.  In my design I am hoping for a quite long exhaust duration and a much shorter input duration, that should be like a conventional engine fully 'notched up',  high speed and not so much torque for minimal air/steam consumption.

My valving concept is much more complex than their's, not to say that mine will necessarily be better though!

John Hill:
Stew, I have a 10mm bore I need to enlarge to about 22mm and it is about 40mm deep, blind hole.  Thats the size boreing bar I need to make but I dont have brazing facilites right now so I need to scratch my head a little to make a suitable tool.

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