"Wild_Bill" wrote in message
...
There aren't many adjustable workholding chucks that are perfectly true to
the center axis.
The more moving parts, the less accuracy.. generally.

Variations in the overall (in)accuracies of individual parts will dictate
the accuracy of a chuck (lathe, drill, etc).

Collets are generally considered to be much more accurate than adjustable
chucks. The adjustability feature of chucks is more for convenience.

Turning a simple part such as a bushing with a shoulder, will most likely
be most accurately machined/turned, when the bushing dimensions are cut to
desired sizes, then the part is cut off.
This is a common practice for very good/excellent concentricity.

Having chucks with soft replaceable jaws allows the user to bore an
axis-concentric hole/bore in the jaws for a particular sized workpiece,
and re-bored for a different size for best accuracy.

The jaws themselves, the guides that position the jaws and a scroll that
engages the jaws for adjustment, are all involved in the overall accuracy
of adjustable lathe or drill chucks.

The jaws typically aren't identical in adjustable chucks (the gear-type
teeth that engage the scroll differ from jaw 1, 2, 3 etc), so it's not as
if one could build a very accurate chuck with only a couple of sets of
jaws.

The big difference in accuracy between chucks, is cost. Accuracy and
quality control are more expensive.
China and India typically make consumer grade products that looky-like a
real item, but quality control and accuracy generally aren't priorities..
just filling up the cargo containers for the next shipment is what
matters.

Accuracy of chucks from other locations will vary, depending upon the cost
and the intended application that they were manufactured for.

--
WB
.........


"Bob La Londe" wrote in message
...
From the Sherline website.

"Due to the nature of the design of a 3-jaw chuck, it cannot be expected
to run perfectly true. Even 3-jaw chucks costing five times more than the
one made for this lathe will have a 0.002" to 0.003" runout. If perfect
accuracy is desired in a particular operation, the use of a 4-jaw chuck
or a collet is recommended. Both are available for your Sherline Lathe."

I don't have a Sherline lathe, but I was considering mounting a small
Sherline chuck on a stepper driven spindle for a fourth axis on one of
the mini CNC mills in the shop.


+1 on the soft jaws! I think it's important to plan a job around the
limitations of your tooling. I only see where the accuracy of a chuck come
into play is on a secondary operation or poor planning. If I have to, I
make soft jaws but I try to avoid the extra work with forethought.