# centre a 4j chuck



## Julian (Nov 3, 2007)

Hi Guys,
I take no credit for this device. I found it on another site. Not sure whether any pf u have seen it but worth posting. Designed by John Stevenson of England.










Method of use.
Always adjust using the opposite jaws at all times ie treat as two 2j chucks. Adjust by eye as near as possible then use the above. Two chuck keys are better than one. Check one set and then turn 180deg. Adjust untill as little change as possible between the 180deg positions. Do the other set of jaws in same way then recheck both sets. Looks a very useful piece of kit so building one now as it is not machine specific.

Tip from John Stevensons text is....adjust the needle so it is as close to the point of the DI as possible.


Julian
in probably-gonna-rain-Leicester


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## mklotz (Nov 3, 2007)

John's a clever guy and one of the most humorous fellows I've encountered.

However, I have to disagree with John on this one.  The quickest way to center something in the 4jaw is to make a clone of the chuck key and use the two keys in concert on opposing jaws to 'walk' the DI needle to the correct point.  John's gadget measures the runout in a vertical direction which means that one of the jaw adjusting screws is pointing down and is difficult to reach.

I find it much easier to mount the DI via a magnet on the cross slide so the runout measured is horizontal and the two adjusting screws needed to take it out are horizontal and accessible.

I wrote an article on this technique of aligning stuff in the 4jaw for our club.  If anyone is interested, I'll post it here or email it to people who want to read it.


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## lugnut (Nov 3, 2007)

Marv, I really like your idea of using two chuck keys in the 4jaw.  Now Im going to turn the John Stevenson DI tool 90° and it should work great!
I do have a magnetic base also, but then I wouldn't have a excuse to build John's tool. :roll: 
Mel


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## compound driver (Nov 4, 2007)

Hi 
Save your self the ass ache of making one just put a floating center between the work and a live center in the tool post and run the DTI on the floating center. Its the recognised method of setting up a 4 jaw.

Cheers kevin


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## Tin Falcon (Nov 4, 2007)

This is what I use. CD is this what you call a floating center??






Tin


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## compound driver (Nov 5, 2007)

HI
thats on the lines but all you need is a dead center and a live center
Dead center goes between the work and the live center thats held in the tailstock.






cheers kevin


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