On 2009-06-29, DoN. Nichols wrote:
On 2009-06-28, Michael Koblic wrote:
DoN. Nichols wrote:

[ ... ]

A scroll-backed (universal) chuck is mostly for quick setup
where the concentricity is not too critical -- e.g. when you are going
to turn all the features in one setup and then part off from what is
held in the chuck.

If you want *precision*, you take the time with an independent
4-jaw chuck to do the setup with a sensitive dial runout indicator.

But another use for a 3-jaw is with either reversed jaws
(assuming one-piece chuck jaws), or with soft jaws turned to make
reversed steps to hold a larger diameter disk shaped object. If you
want to handle even larger, make a set of extra-long soft jaws for the
3-jaw you have and bore them to a close fit so you can clamp the jaws
onto the workpiece with very little motion of the scroll plate. You
don't really need precision centering for this, because you will be
using it to face the workpiece not to turn the OD.

I saw this today, and bookmarked it to post as relevant to this
part of this thread:

http://www.frets.com/HomeShopTech/Projects/Bison/bison.html

scroll (way) down to where you see:

================================================== ====================
Part Two - Extra Long Soft Jaws
================================================== ====================

(It looks like it is about 2/3 to 3/4 of the way down the web page.)

Anyway -- this is what I was talking about for making the long
soft jaws. You can also see the difference in the way the jaws are made
by comparing the first photo with your jaw. It has more features to
assure alignment. By the end of the page, you can see it being used to
make a disc like what you would use for your sundials.

Enjoy,
DoN.

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