"JWho" wrote in message
news:rutcf.556945$xm3.194111@attbi_s21...

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oups.com...
JWho wrote:

HUM! I think I see what is meant now! One can work on a rod longer
than
10" as long as it is 5/8" thick or less, correct? Assuming that is
correct,
then your points on it being more and more wobbly as the rod got longer
makes perfect sense. Right now, I can only think of two parts I would
ever
make, and neither is longer than 10". Before this, I thought every rod
had
to be inside the two centers.

Actually you can't work a thin rod anywhere near the capacity length of
the lathe, because it will flex and chatter, rubbing against the tool
rather than cutting smoothly. You can probably only turn something a
few diameters long that is hanging out of the chuck, a bit longer if it
is also supported at the tailstock end. With something really long and
thin, you could work an area near the headstock, and a shorter area
real near the tailstock center, but not in between. And you'd have
trouble drilling the hole for the tailstock center, since you couldn't
support the work near where you'd be drilling.

I'm going to guess that for half inch stock, the practical limit for
chuck support is less than 3" maybe 4.5 or 5" if you support the other
end with the tailstock. Could be wrong though, lathe has been in
storage fora few years.

All that you mentioned is just for a rod that is over 10" though, correct?
I think the thing I would want to make is about 8" or 9". I can envision
what you mean on it wobbling. It would be like a fiberglass rod. Pretty
soon it is like a lasso. :-| Sounds dangerous!

The rule of thumb is never to go more than three diameters unsupported ..
and that is pushing it. If the job is done between centers, or between a
chuck and a tailstock center, then it is supported on both ends and you can
go 4 to 6 diameters without intermediate support. You can go longer and
thinner than this in two (actually, three) ways.

1. Very carefully, with very careful adjustment of the tool height, light
cuts, and very, very, sharp, properly sharpened, tool bits.

2. Use a steady rest. This is an intermediate support that stays fixed on
the lathe bed. Gives you an additional support point. A bit of a PITA if
you're machining the whole length because you have to move the steady rest
if it is on the spot you want to machine. Has to be reset for each pass.

3. A movable steady rest.. called a "follower rest." This attaches to the
carriage and moves along with it... typically behind the cutting tool. Has
to be reset for each pass.

A word of caution on long things in small lathes that fit through
the headstock. If the stock sticks out of the headstock's left end more
than ten or twenty diameters, it will wobble, and eventually bend. This
happens quite catastrophically since the more it bends, the greater the
centrifugal force that makes it bend even more. The least it will do is
bend your stock to uselessness. Somewhat worse is deep gouges in your
workbench, or even worse, removal of sundry body parts that are in the
region.

Boris

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