wrote in message
ups.com...
JWho wrote:

When you say chuck, is that similar to a chuck on a cordless/electrical
drill, just special for a lathe? It's for holding a tube or rod or
similar,
correct?

At the bottom, it has, "Through chuck capacity: 5/8" ". Is that the same
as
"through hole in the headstock" that you mentioned? Would that make it
unable to use some size of solid rod, or would it just make it less
convenient or use more rod?? I am not 100% sure what that means to me.


As another example, suppose you wanted to machine some fittings at both ends
of a long shaft. Say 15 feet long or so and that you just wanted to turn 2"
at the ends down to 1/2" say. If the through hole in the headstock is 1/2",
then the largest diameter shaft you could turn would 1/2". If the headstock
hole was 3", the maximum shaft diameter would be about 3" .. in both cases,
the length is limited by the room you have in your shop to the left of the
lathe because only a little bit has to stick out into the working part of
the lathe -- the 2" length you wanted to machine. Now suppose that you
headstock hole is 1" and you want to turn the ends of a 10 foot shaft, 1.5"
in diameter. Can't be done on that lathe .. at least not with reasonable
convenience. You would be limited to a length slightly less than "the
distance between centers."
The hole through the headstock is generally much less than the hole
through a chuck. That's a property of the chuck, not the lathe. Of course,
if you have a 3" hole in the chuck and a 1" hole in the headstock, you can't
push your work further in than the point at which the work touches the
spindle.... at least not twice on the same lathe.
The size of the hole through the headstock is far more important in
a production setting where the material is being fed through the headstock
to the cutting tools. Since most home shop machinists rarely turn long,
large diameter, shaftings, the issue is mostly a matter of convenience and
wasted material, as pointed out earlier... until, of course, that day when
you absolutely must have that larger diameter.
That's the first order approximation. Now for some refinements of
the idea. You should always keep the working part (the place you are
cutting metal) as close to the headstock as you can. That cuts down on
chatter (you'll learn about that soon enough), and makes it easier to hold
accuracy all along the piece. A long piece much be held at one end by the
chuck and at the other by the tailstock point. The longer that distance,
the wobblier the work becomes .. with many attendant problems. For that
reason, working long pieces not partly in the headstock means you'll have to
use a steady rest or a follower rest or both.
The third order approximation... For very accurate work you do all
the machining between centers, with nothing stuch through the headstock
hole.

Get hold of the lovely little book "How to Run a Lathe", originally
published by South Bend, but now available very reasonably from Lindsay
publication.


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