4jaw centering tip

[mklotz]

In my little treatise on centering work in the 4jaw chuck...

http://www.homemadetools.net/forum/c...aw-chuck-27241

I advocate mounting a dial indicator to a permanent easy-to-set-up arrangement. A typical arrangement would be to fabricate an aluminum piece to mount on the QCTP and bolt the DI to that. Then, when centering, the DI can be slapped onto the QCTP, automatically aligned with the spindle axis, and you're ready to start moving chuck jaws.

The referenced procedure has you touch the DI to the work, adjust to roughly mid scale, and align the DI pointer with zero on the scale.

Now, here's where the hint comes in. Adjust the DI scale so zero is at your 3 o'clock position. Following the instructions, the DI needle will point to this 3 o'clock position.

Turn the chuck 180 degrees. Because the work is not centered the DI needle will no longer point to zero. But now, ITS POSITION WILL GIVE YOU A VISUAL INDICATION OF WHICH WAY TO MOVE THE WORK. If the needle is at the 1 o'clock position, it needs to be moved toward you and, so, the work needs to be moved toward you; loosen the front chuck jaw and tighten the back one. If the needle is at the 5 o'clock position, it needs to be moved away from you and so must the work; loosen the back jaw and tighten the front one.

Using this hint is not essential to the procedure but it does make the movements involved a bit more intuitive.

[Frank S]

Thanks for sharing this Marv. I have used this method for years mostly because I am both left handed and partially dyslectic having the needle move towards me or away from me by using the 3 o'clock zero positioning I don't have to think twice about which way the work piece needs to be moved
However on the lathes I have now I have not as of yet made a permanent or easy mount to fit either of my Qctp's yet I still use the LS Starret V block magnetic mount for my DI

[Toolmaker51]

Same here. Slapping rough stock in a four jaw isn't about the exterior so much as solid stock below. I don't follow the 3 o'clock method in precisely same manner, but make slight contact to find the 'high side' and give the face a dab of felt pen. Rotate 180*, estimate [or re-position the DI for contact] distance off center. Halving that shows how far to move the part.
Another trick is with chalk. Rotate the item, marking close to apparent center or layout center. The error will be apparent as a starting point. Great for castings or irregular forms unsuitable for DI.
Note to self. Replace a long lost pump or centering wand... thinking about a ball and conical seat, machined in a spring and plunger [maybe half universal joint device]. Most lathes around me are 16" and larger swing, so figuring the wand should be equal length minimum of .200 dia. something drill rod?