On Thu, 15 Mar 2012 14:48:50 -0600, Pete C. wrote:
Tim Wescott wrote:
On Thu, 15 Mar 2012 14:07:34 -0500, jim wrote:
Tim Wescott wrote:
On Thu, 15 Mar 2012 12:10:40 -0600, Pete C. wrote:
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.
http://en.wikipedia.org/wiki/Schnuerle_porting. See the picture in
the upper right. Now imagine that instead of having two transfer
ports feeding gas to the cylinder, there's four; the two shown, plus
two more that are rotated more away from the exhaust. Then, if
that's not enough, a fifth "boost" port directly opposite the
exhaust, and pointing toward the top of the cylinder.
The whole idea is that the transfer gas hits the pocket at the
cylinder/ piston junction, then rises up the back of the cylinder in
a fairly unified mass; because this mass is increasing in volume, it
naturally pushes the spent gas out the exhaust port. Cross-flow
scavenging (the kind where there's a fence on the piston) tends to
mix the gases a lot more.
There's a lot of hand-waving explanation for why it works, but the
bottom line is that it works better than cross-flow scavenging!
I don't see why you need holes with square sharp corners to achieve
those port configurations.
Well, you don't, in general, which is why I'll probably just use round
holes to start. But if you want the maximum flow in the minimum space,
you do.
--
Tim Wescott
Control system and signal processing consulting www.wescottdesign.com
Looking at the pic, it still looks like you could get the desired port
with a small dia slotting saw. It will leave you a bit of a funnel
opening on the outside leading in to your square / rectangular port.
Well, I disagree. I think that if I did that I'd end up with undirected,
turbulent flow in exactly a spot where I wanted directed laminar flow.
--
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