Thanks to all who replied to my query. As suggested, I looked at
Rick's design for an adjustable backplate and realized that part of
his solution is a deliberate mis-match between the sizes of the land
and the recess. Given that I had this mis-match already what I
needed was a more controlled method of adjustment rather than my
crude tapping technique -- my lazy man's approach is to use the cross
slide as the adjusting screw for centering the chuck.
What I did was put a large (5/8) center drill in the chuck to use as
a shaft for measuring runout, chucked so it extended enough to allow
access to its HSS shaft. The indicator was set up to measure runout
at the rear of this shaft; the chuck was turned to place the low
point at the rear, thus placing the high point toward the front
(where a tool in the toolpost would contact it).
With the nuts on the chuck barely snug I placed a 1/2" square piece
of mild steel in the tool holder and attempted to use this to push on
the shaft of the center drill to slide the chuck to center. This
didn't work initially, apparently because the force is too far from
the backplate. However, by applying enough force via the cross slide
to move the indicator to the desired reading then loosening and
tightening each chuck nut in succession I was able to set the TIR to
better than .001 fairly quickly on each of several tries. Much more
controlled than my original "thump it" approach.
John
--- In 7x12minilathe@..., "John <moran03@e...>"
<moran03@e...> wrote:
The raised land on my spindle plate measures 2.154 rather than
2.165
as given on the mini-lathe site. Sure enough, the recess in the
chuck
measures 2.165.
In order to mount my 3 jaw chuck I first snug the nuts slightly,
put
a rod in the chuck, and use an indicator on the rod. I rotate the
chuck so the high point is up and tap the chuck on the top with a
block of wood; this is not a well controlled process so it
typically
takes several minutes to get TIR between 1 and 2 mils, when I
tighten
the nuts.
Is there a better way to center the chuck?
Is the mis-match between the land and the recess common? I expected
the chuck to center itself on the spindle land but this mis-match
apparently precludes that.
John
