"Richard Smith" wrote in message ...

"Jim Wilkins" writes:

...eccentric...

Variable - you have many eccentrics, each with a slightly different
throw?

I thought - one eccentric, but many different "pistons" with their
"collar" they go through into the fluid volume.

-----------------------

One circular eccentric disk, mounted on an offset pivot pin so it can be
centered or swung out as needed. The clamp for the swinging side might have
to include a custom stepped bushing to withstand the torque, rather than
just a bolt that holds by friction, but its surface finishes aren't critical
like the eccentric's. Lathes don't necessarily leave surfaces good enough to
be running bearings, that's extra hand work.

It's easy to turn two cylindrical surfaces with different centers when
holding the work in a 4-jaw lathe chuck.
http://s3.cnccookbook.com/CCLatheEccentricTurning.htm

The eccentric disk could be a slice of hydraulic cylinder rod with a
case-hardened, chromed and polished surface. The strap could be lined with
replaceable slices of Oilite bushing. You don't need the historical accuracy
many British model engineers strive for.
http://www.stockbridgelocomotivework...nd-valve-gear/

You have ideas that need machine tools to create. Good new ones and hired
custom shop work are quite expensive, so I saved by finding older industrial
machines which had become obsolete and too worn to be economical in a
production shop, like a lathe made in 1965. You have an excellent
equivalent:
http://www.myford-lathes.com/used.htm
I have no experience with the current imports.

I can't easily hit the tolerances on a customer's drawing but I can still
make two pieces fit each other although they may not be quite to spec, so my
antique machines are fine for making single devices for my own use (and for
fixing each other). From the reference above:
"I turned the final diameter on a good portion of the bar and then machined
each eccentric one at a time, individually match-fitting each eccentric
strap."

The trick is that two parts of a complementary operation may not be equally
difficult, for example the piston is easier to turn and finish than the
cylinder, so make the difficult one first and fit the easier one to it. The
boring head he used on the eccentric has a micrometer adjusting screw to
change size, I have an identical one. Many shortcuts are possible when you
control the design.

I made the prototype of an inch-long diode laser and lens mount in a few
evenings that later cost $4000 apiece from a job shop that normally made
parts for BAE. Mine wasn't quite as well finished but it worked and proved
my ideas. First I needed approval to charge it as overtime, but the project
engineer knew how expensive the company's main machine shop was. I suspect
part of the high cost was due to the electrical engineers' inexperience with
mechanical design and machining.