"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
Hello Bob,
I have a Bison 6-1/4" (it's actually 160mm) independent 4-jaw chuck. I think
you will be very pleased if you bought this chuck. The no-name (usually
Chinese) chucks are hit-or-miss...you really have no idea what you'll be
getting. The Bisons are inspected and certified (and very well made).
In any case, if you decide to go with the no-name, then you should skip the
one with the threaded back and get the plain back #271-6005 (currently on
sale for $59.99). That way you can machine your own back plate on YOUR OWN
lathe. This will ensure that at least the chuck mounting surface is
concentric with--and perpendicular to--your spindle.
& 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.)
It'll work alright...after you machine off about 8 lbs of cast iron! You
see, many 4-jaw independent chucks (including the Bison 6") do not use full
back plates. They use something more like a "back plug" that fits into a
recess in the back of the chuck. The mounting bolts are positioned near the
center axis of the chuck which is why the adapter plate doen't need to
extend to the full diameter of the chuck. (Whereas, on a scroll chuck, the
bolt are near the outer periphery in order to clear the internal scroll
mechanism.)
According to Bison's tech manual, the 160mm 4-jaw independent chuck requires
an adapter only 82.55mm (3-1/4") in diameter. So all you really need is a
piece of machinable steel 3-3/8" in diameter and roughly 1-1/2" long (length
depending on your actual spindle mount requirements). Of course, you can use
seasoned cast iron if you can find a piece like that.
(Note: this info in the last two paragraphs are specifically for the Bison
6-1/4" chuck. I don't know the requirments for the no-name plain back--and
you probably won't either until you get it. Some 4-jaw independents do
require full-sized back plates.)
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 Bison is machined to higher quality standards and is inspected and
certified during QA. Presumably, those chucks that don't pass inspection
never make it to market.
Of course, that doesn't mean you can't get a no-name that is as accurate as
a Bison (or other quality branded chuck). But I don't think you'll really
know what you're getting until you have it mounted on your lathe.
I expect that the chuck will get very little use, so durability
is not something I need.
You might find yourself using it more than you currently expect. The 4-jaw
independent has the potential to always be more accurate than a scroll
chuck. Once you get a good one and become experienced with it, you'll find
it doesn't take long to get it set-up.
If I get the Bison, how fussy would I have to be in finishing the
semi-finished back plate?
You should be as fussy as you can, of course. Seriously, the mating surfaces
for the spindle shoulder and for the chuck recess should be very well
finished and a very close fit. Or, as Bison says: "Centering surfaces of the
adapters should be fayed against the chuck body with the clearance the
smallest possible."
Some argue that the threads on threaded spindles are also partly responsible
for keeping the adapter (and chuck) located with respect to the spindle, so
they should also be well-finished and of close tolerance. You should make a
mock spindle plug that is an exact copy of the threaded portion of your
spindle nose, including the locating shoulder. That way you can test the fit
of your adapter while you are machining it (you obviously do not want to be
taking it off during the machining process to test against your actual
spindle nose).
Regards,
Michael