View Full Version : Adjusting a 4 jaw chuck

Kerry Pinkerton
01-23-2004, 04:13 AM
I making some anvils and decided to chuck my mandrel in the 4 jaw. HALF AN HOUR LATER I finally got it adjuster to within a thousandth. It should have taken a LOT less time if I knew what I was doing and didn't spend most the time going the wrong way

I'm sure there is a process for this. Help?[/b]

01-23-2004, 05:45 AM

I use a center iinserted in my headstock and a mandrel which is center drilled on both ends. The only thing I use the chuck jaw for is to catch the 1/4" drill rod drive pin I insert into the anvil. The great thing about this is you can remove the mandrel and put it back without losing your setup.


Kerry Pinkerton
01-23-2004, 06:27 AM
Thanks Ralph, that isn't much different from what I do. my question though was what is the best process to adjust the 4 jaw CHUCK for holding the center or mandrel true?

01-23-2004, 06:53 AM
An EZ way is to mark the chuck jaws that are180 Degrees apart with a magic marker or dychem or ?
When you adjust first use 2 jaws to run appx. true then adjust the other jaws then fine adjust.

Also keep in mind the pressure (tightness) you put on the chuck wrench can have a very large effect.

What are you using to measure the runout with?

Hope this helps,


01-23-2004, 07:18 AM
What is needed is a center that matches the taper on your headstock bore. What makes this process repeatable is that the center is inserted into the headstock taper and the center drilled mandrel is mounted to that. There is no need to use the four jaw chuck to hold it at all.

To adjust a four jaw chuck accurately adjust the jaws by visual reference to your tool until its close, then use a solidly mounted dial indicator close to the chuck and adjust opposing jaws. I find that I do better adjusting one set of opposing jaws, then the other. After you get it close at the headstock end move to the tailstock end and check it there, adjusting with a soft hammer. Recheck the headstock end and your done. I find it helpful to use some soft tabs of aluminum under the jaws to keep from marring the work. Remember that round stock isn't always round or straight!


01-23-2004, 06:15 PM
Hi Kerry,

Just to add a wee bit to what has been said here's the way I have been taught: (I will repeat in entirety for clarification)

Using the concentric circles found on your chuck - you rough adjust your jaws (by eye) onto your part - but only clamp lightly

For the sake of the example let's label the jaws:
The jaw at the 12 o'clock position is jaw 1
The jaw at the 3 o'clock position is jaw 2
The jaw at the 6 o'clock position is jaw 3
The jaw at the 9 o'clock position is jaw 4

Put your dial indicator in place - and zero it on jaw 1,
Rotate the chuck until the indicator is on jaw 3 - read the indicator, it is now reading DOUBLE the amount you need to move it. loosening/tightening jaws 1&3 appropriately tweak it unitl the indicator reads 1/2 of it's jaw 3 reading (you do not have to rotate the chuck) - do not yet "crank" the jaws - just snug them ( 1,3)

Now repeat this for jaws 2 & 4.

With all jaws snug you can crank each one tight - If you leave the indicator in place you can monitor the amount of wiggling around due to tightening and adjust accordingly.

Since you are rotating to tighten each jaw and watching the indicator when you are now ALL TIGHT there are NO SURPRISES. Give it one more whirl just for luck and the indicator ougth to be a stone - you're done!!! :lol: Piece of cake!!! :roll:

Jacin in Ohio

01-23-2004, 08:18 PM
Thats why I suggested marking 2 jaws 180 degrees apart. It helps to have you (or me) NOT chasing your own tail trying to center the piece.


01-23-2004, 10:08 PM
Hi Rob,

You made a good point - I was merely trying to expand on what you already said :oops: in a sorta step by step version.

(one of my "hats" at work is to write instruction manuals for... as such I have a hard time shifting gears - we try to spell everything out)

Jacin in Ohio

01-24-2004, 05:00 AM
Thanks Ralph, that isn't much different from what I do. my question though was what is the best process to adjust the 4 jaw CHUCK for holding the center or mandrel true?


Adjusting a 4 jaw chuck is like life, you learn from experience. IMHO there are no tricks to this process. I usually just run up the tool bit near the work piece and eyeball the adjustment. When all looks good out comes the dial indicator for the final adjustment if needed.

01-24-2004, 08:53 AM
Kerry: I usually get it it the general ballpark using the machined rings on the front of the chuck. Then turn the chuck by hand to see how close it is. Then I turn on the spindle and take a sharpie and touch the stock with the tip of the sharpie while turning. Shut down the machine and check where the mark is located. If the mark is in line with the plane of a pair of jaws,then you only need to adjust those jaws. If the mark is between jaws,you need adjustments of both sets of jaws. Rotate the chuck until the ink mark is on top. Tighten the jaw that has the mark loosen the jaw 180 degrees away from the mark. Turn it on and put another mark with the sharpie. If the mark goes all of the way around, You are very close. Generally closer than what I get with a 3 jaw.
I got to thinking about another possible way that I have not tried yet. I suppose that you could take a depth mike or caliper and measure how deep the jaw is in the chuck. If you use a digital caliper,measure the depth of #1 and zero your caliper at that depth. Then measure the depth of the other jaws and the caliper will give you the difference.
It would probably be good the get a piece of stock zeroed and then do a jaw depth measurement to see if the jaws are all at the same depth. If they aren't, record that number for future use. Dress the end of the jaw to make them all the same depth when zeroed. Does this make any sense?

06-19-2004, 07:36 PM
Hi Kerry
I realize this reply is a little late, but also a little different method I use to solving your problem. It is fast.
1. Round stock----- Scribe center lines on the end of your workpiece to find center. mark the center.
2. sq. or rectangluar stock.---- mark the center you want to revolve around.
3. Put the sharpest center you own in your tailstock and move it up to your workpiece.
4. Adjust jaws till center mark matches tailstock center.
5. Dial in balance with indicator and follow suggestions of previous
threads (jaw tension etc etc )
Works for me. Personally I always use my 3 jaw for rounds except when I'm turning something that isn't concentric.