On Sat, 24 Mar 2007 12:45:41 +0000, Andy Hall
wrote:

That was one of my concerns - if there is a lot of backlash, or worse
still a tendency to move, it would be a bit useless. I suppose
that some replacement of screws could help.

The 6" one I have is about 8 years old and similar to the Chronos one
in looks. I was looking at a Chronos one a month or so ago and it
looked better finished than mine was (which reflects the significant
improvement in quality in the last few years). That said the only
work I did on mine to make it respectable was to throw away the
various plasticine grub screws and replace them with real ones. The
basic machining of the cast iron was fine.

Don't forget that both ways (x and y) have an adjustable gib strip
and three adjusting screws with lock nuts on each strip to enable the
dovetail to be adjusted to remove excess play. The gib strips on mine
I polished a little bit with a fine file to give a smoother movement.
With the adjustable gibs you can control the stiffness of movement
easily and take out any slack on the ways. When correctly adjusted
the vice is very solid.

There will always be a bit of backlash in Acme threads as they have
limited clearance at the major diameters of the external and internal
threads so that a bearing at the major diameter maintains approximate
alignment of the thread axis and prevent wedging on the flanks of the
threads. However it's more of an issue with positioning systems
where you have to approach the target from either direction. If your
concern is more about how stable the vice position is I don't think
you need worry. Once you have adjusted the gibs (not something you
need to do often) the vice certainly won't move when drilling, there
is no creep at all
--
Peter Parry.
http://www.wpp.ltd.uk/