On Tue, 30 Nov 2004 18:34:19 -0800, "Kelly Jones"
wrote:

Off the deep end? Perhaps. But the original question was about how to
check the rack and pinion, not whether it should be checked. I appreciate
you pragmatisism, but it was still fun to describe how to do a pattern
check. Whare's your sense of humor?

My sense of humor disappears very quickly when it goes from the realm
of the ideal to the realm of the ridiculous. A patten check on the
hypoid diff gears that I used to do by the dozens is one thing, on a
rack and pinion, where the rack is die cast and the pinion extruded is
senseless. I could have gone into the whole nine yards of a gear lab
check, but to what end? In this particular application, if the spur
gear has .0002" helix, and the involute error is .001", what's the
difference? Even pitchline to pitchline makes no difference here, the
pinion is crushed into the rack for full engagement by a spring, and
the relation of the pitchlines really don't mean squat. DP of the
rack and pinion is going to be probably 32 or finer, you're looking
for errors that are going to be in ten thousandths, and even if
they're found, they won't bother anything. Even my 35 year old
Edmonds, the focusing isn't perfectly smooth, but it doesn't make one
bit of difference, it still works just fine. There are some focusers
out there that are perfectly smooth, or as near as is possible, but at
$300 or so per copy. To what end? The mirror in my 10" f8 cost me
$350 for figuring and coating, I don't think a $300 focuser is going
to make it work any better. It has an off the shelf Boston rack, and
the pinion cut from pinion wire. Works just fine, and a hell of a lot
cheaper.

Why complicate things?