On Sun, 24 Aug 2003 16:33:02 -0400, Bob Engelhardt wrote:
I'm about to buy a 6" independent 4-jaw lathe chuck. ENCO has their
free shipping promo on this month, so I was looking there.

They have a no-name with threaded mount for $99.95 (ENCO #271-6382):
http://www.use-enco.com/pdfs/157.PDF

or

Bison plain back for $156.95 (ENCO #240-3064):
http://www.use-enco.com/pdfs/160.PDF
& it's "semi-finished" threaded back plate for $43.95 (BTW it says this
back plate is for self-centering scroll chucks, do you think it'll work
with the independent jaws chuck? There's no finished back plate shown
explicitly for the independent jaws chucks.)

I do believe that you get what you pay for, but I also believe in buying
what I _need_, even if it's not always the "best". So, what does the
$200 Bison have or do that the $100 no-name doesn't? With an
independent 4-jaw, all you really need is that the jaws are parallel to
the spindle axis, right? How much worse will the no-name be than the
Bison in this regard?

The no name threaded chuck leaves you at the mercy of the
chuck manufacturer *and* your lathe manufacturer as far as
it being concentric, and with the face and jaw slots perpendicular
to the spindle axis. If it isn't, there isn't a whole lot you can
do about it. You can grind the jaws in place to correct for a
small amount of error, but that generally isn't desirable.

With the plain back chuck (and Bison is good) it is up to you
to machine the back plate true. But since you'll be doing it on
*your* lathe, it should wind up perfectly perpendicular to your
lathe axis. How could it not? So that's generally the better
way to go. It allows you to remove any tolerance stack up or
manufacturing errors that your lathe manufacturer or the
chuck manufacturer may have made.


If I get the Bison, how fussy would I have to be in finishing the
semi-finished back plate? My lathe experience was in high school shop,
45 years ago.

You have to face off the semi-finished backplate, it is already
threaded for your spindle, and then spot and drill it for the chuck
mounting bolts. It isn't a particularly fussy job, and you want a
little slop in the mounting holes so you can adjust the chuck to
run dead true when you mount it.

Gary