On Thu, 15 Mar 2012 14:11:59 -0700, Bill Martin wrote:

On 03/15/2012 10:14 AM, Tim Wescott wrote:
On Thu, 15 Mar 2012 09:36:39 -0700, Stanley Schaefer wrote:

On Mar 15, 9:54 am, Tim wrote:
How would one make nice sharp-cornered, clean-sided (I'm not sure of
the surface finish, but mirror-bright would be nice) square holes,
about 0.1" on the sides, off center from the axis of the bar (so not
square to the bar surface), in a round steel bar about 0.75" in
diameter?

Alternately, how might one make those same holes in a cylinder
machined out of that same bar, with a wall thickness of about 0.06",
without distorting the cylinder by more than a couple of thousandths
(I am assuming that one would have to do some post-operations to
clean up the cylinder after making the holes, unless one hand-filed
them).

This is a thought experiment for making cylinder liners for 2-stroke
engines of about 0.2 in^3 displacement; the holes would be the
transfer ports, and the cylinder liners need to have their diameter
controlled to about 0.001" on the outside and less than that on the
inside for proper sealing (or if not controlled, then at least
matched to the crankcase that they slide into, and the piston that
slides in them).



How about you turn it inside out so it's an external slotting/milling
operation? :-)
That's not as nutty as it sounds...mill your transfer ports into the
outside of the cylinder proper, than press a hollow tube (sleeve) over
the outside. Presto, you have transfer ports! One thing that is going to
be a problem though: steel/iron doesn't get the heat out very well, and
two strokers have a lot to get rid of. Good luck,

The standard construction for model airplane engines of this sort is to
have a cylinder lining of steel or (if you have friends in the right
sorts of shop) hard chromed brass. It's a thin tube, usually with a lip
on top, that slides into the crankcase. The crankcase has passages cast
or milled into it for the transfer and for the exhaust.

So the gas travels up from the crank case to the port along the outside
of the sleeve, then turns 90 degrees to go into the cylinder. Meanwhile,
the exhaust is exiting through its port without (we hope) leaking into
the crankcase because the liner is sealed to the case by a close
mechanical fit.

I'm not sure of the detailed heat-flow -- I just know that it must be
adequate, or all my engines would have burnt up long ago.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com