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 handles, 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 lot 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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