Tim Wescott wrote:

On Thu, 15 Mar 2012 10:20:42 -0600, Pete C. wrote:

Tim Wescott 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).

--
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

Wouldn't this normally be just a milled slot? Square on the top and
bottom (relative to the piston stroke) with the edges running off the
cylinder leaving square "knife edges" at the ends? At 0.1" perhaps a
pass with a slotting saw rather than a super small and delicate end
mill.

Schnuerle ported engines want transfer ports that direct the gas toward
the cylinder wall away from the exhaust port -- that tends do a good job
of blowing out mostly spent combustion products, while retaining the most
possible unburned fuel/air mix. More power, better fuel efficiency,
cleaner burn -- what's not to like? (Except for the difficulty in
machining, of course).

--
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

I'm having a little difficulty picturing exactly what you're trying to
do. Perhaps drill and broach? You can make your own broach a bit more
easily than the ECM and EDM lines of thought. Come to think of it,
perhaps rotary broaching might do what you need.