>>>Dave Williams said:
> > They only measure at two points, and you can
> > miss an outof round condition.
>
> How else are you going to find an outofround condition? You turn the
> guage 45 or 90 degrees and measure that way. The difference tells you
> out of round.
There are an infinite number of figures with constant width that are NOT
round.
The simplest to describe is a sort of rounded triangle: take an equilateral
triangle, set a compass to the length of the side, place the pin in each
vertex in turn and draw an arc connecting the other two vertices. When you
are
done, the three arcs thus drawn form a figure of constant diameter  you can
make rollers with this crosssection, place boards on them and roll along.
The
boards will NOT go up and down but will roll along smoothly.
Other examples are left as an exercise. Show your work for full credit.
The Tgauge will not detect this kind of out of roundness.
Whether this is of practial importance is another question, because I don't
think worn cylinders achieve this sort of shape. Certainly measuring at
several angles will detect an OVAL cylinder, the most likely (I think) shape
in
a worn engine, but it won't detect ALL (in the strict mathematical sense)
outof roundness.
I could be wrong; I haven't measured a lot of engines.
berry
Berry Kercheval :: kerch@parc.xerox.com :: Xerox Palo Alto Research Center
