Joseph Gwinn wrote:
I think I've figured out a big piece of the mystery of what I
generically called chatter in the "Clausing 5914 Chatter ..." threads.

Tightening the lathe dovetails up helped a great deal, and is a good
idea in general, but didn't really solve the problem.

It came to me in the shower Wednesday morning - self-feeding would
explain just about everything seen, and that if one reverses something,
the sign of the mechanical feedback loop can be reversed.
Yes, of course, you are dead right! But, proper serup of the
tool and how it relates to the toolpost, compound swivel, etc.
can make a big difference. You mentioned in an earlier post, I
think, that interference with the chuck jaws required you to
have so much overhang, so that points out that better work
holding would reduce the problem.

I had some real problems doing these types of operations on
Atlas/Craftsman lathes. The 5914 is a MUCH sturdier lathe with
a much heavier bed casting, so I'm surprised you were having
this sort of trouble. I finally traded up to a Sheldon R15-6,
which is an even heavier lathe, in the 3000 - 3500 Lb class.
You can stand on the bed with no measurable deflection (and I
have precision electronic levels that are REALLY sensitive).
It is amazing what a difference stiffness of the lathe makes.
Now, another comment is that you may have a poor "fit up"
between your carriage and bed. I totally rescraped my bed and
carriage to get the best fit between these surfaces. In my
case, due to the hardened bed, I had to grind it with Cratex
polishing wheels and then lap it smooth with bench stones.
(A carbide scraper blade wouldn't even SCRATCH the bed.)
I then used Moglice castable way liner to make the underside of
the carriage conform to the bed.

But, after all that work, I have no problem parting-off or with
other jobs where there is a bit of overhang. I haven't done
anything with quite as much overhang as you needed on this jb,
but my guess is there is somthing in your lathe that is "not
right" and allowing maybe the carriage to rock about some local
high points. Sometimes you can see this if you take the way
wipers off. You might be able to see the oil fillet between the
bed and carriage "pulse" a bit as force is applied to the
carriage. That is a dead giveaway that the carriage is rocking.

Jon