Rapid centreing of a 4-Jaw chuck.

This may be common knowledge to some, but being able
now to centre a 4-jaw chuck in a couple of minutes instead
of spending 20 minutes cussing and swearing is an absolute joy!
I do not claim originality for this, I was shown it in my turn.
The essence of the trick is that you need _TWO_ keys for your
4-jaw chuck. With the extra key, you can effect a smooth linear
transition of the workpiece across the chuck by simultaneously
releasing one and tightening the other, at all times retaining the
workpiece in a tight grip. No more will small rods fall out and
disappear in the interval between loosening one jaw and tightening
the other!
(I actually made up two extra keys, using 1 and 1/4 inch round bar for the
and squared-off 10 mm round rod for the working end because the
Tommy bar on my original as-supplied chuck key fouls on the lathe body
and it is not possible to do the simultaneous loosening/tightening. Also,
a piece of 1 and 1/4 inch bar sits nicely in the palm of the hand and is a
easier to twirl than a Tommy bar)
The Technique.....
1. You need a dial gauge set to centre height on the cross slide
(I have mine in a Quick-Change tool holder)
2. Place the workpiece in the chuck and approximately centre
by eye. This stage is important because if really badly off-centre,
you won't be able to transit with one pair of jaws because the
workpiece will foul on the other pair being closed up too
far below the diameter. (Thereby hangs a tale, was demonstrating
last night!)
3. Put one set of jaws horizontal.
4. Bring dial gauge up, in line with the horizontal jaws, and using the
cross-slide, wind it on a couple of turns so that it will give both
positive and negative readings.
5. Set the dial gauge to zero, either by its movable cursor, or with
further cross-sliding.
6. Rotate the chuck 180 degrees, ignoring what may appear to
be a large error of eccentricity on the way round, so that the other
jaw of the pair is now horizontal.
7. Read the dial gauge and note the value
8. Without moving the chuck, use the cross-slide to adjust the dial
gauge by the cross-slide so that it now shows HALF the difference
between the two 180 degree positions.
9. Use the two chuck keys, one in each hand simultaneously, and transit
the workpiece so as to bring the dial gauge to zero.
10. One set of jaws is now centred! Repeat steps 3 to 9 for
the other pair of jaws and, Voila!! Zat is Cointreau!
There you are, dead easy, and it takes a lot longer to explain than to do!
Reply to
Airy R. Bean
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