how do you center a 4 jaw chuck ?

[welder]

Hi can anyone give me tips on how to center a 4 jaw chuck. i must have watched all the videos on you tube and all seem to say line it up with the rings (i can do that) then get the indicator measure the highest point half that and bring to zero. but i just cant get it i can get close but never quite centered.

[Stustoys]

Hi Welder,
You're talking about round work?

I don't worry about the high point and such. I set the indicator at center height at the front with one pair of jaws level. Rotate chuck 180degrees, using two chuck keys I them move the work to split the difference. Rotate 90 Degrees set the work to the same number. Repeat. Once you are really close do each pair one at a time.
Hope this helps
There was a thread on this not long ago, I'll have a look
Stuart

[Gavin Newman]

Assuming it's round stock, you can get it close with reference to the rings on the chuck face, then you put a dial indicator running against the work and rotate the work by hand. To make it easier I have the DI mounted in my tool-holder

1) Find the lowest reading and set the DI to zero then rotate until you find the highest point. - Example : Low = 0, High = 25.

2) Work out the average of the 2 readings - Example : 12.5

3) Rotate the work so one set of jaws is in line with the DI plunger and adjust those jaws so the DI reads the setting from step 2.

4) Rotate the work so the other set of jaws is in line with the DI plunger and adjust those jaws so the DI reads the setting from step 2.

At this point the work will be centered. Using 2 chuck keys in the opposing jaws makes it easier, I have a cut-down key I use in the far jaw to clear the splash back.

If you are centering non-round stock you need to make a punch mark in the work where you want the centre to end up. Use a pump centre in that mark and use the centering method against the pump centre shaft.

[pipeclay]

How long is the work you are setting up?

If its a long piece,say 125mm/5.000" out from the end of the chuck jaws you will have to set it over 2 spots.

1st at the chuck,then at the outerend,you would then need to set again at the chuck end and repeat at the outer.

Most times with the longer jobs the final checking will be done at the chuck to get zero then the outer end tapped with soft hammer to zero,then a final check at the chuck,it can take a bit of chasing.

If you were setting work close to the chuck,roughly set the job by the rings on the chuck face,scribing block or your tool.

Once you have the job reasonably true and if you can set to a machined surface that is cylindrical use your indicator.

Dont have the jaws done up to tight when setting up.

Set your indicator on zero get a marker and mark on the chuck the deviation around the job being either (+/-).

This deviation will change as you set the job.

Dosent matter which jaws your set first as long as they are opposite.

Move them half the runout,when it gets down to only a few thou or hundreths just cracking the jaw and tightening the other can be enough to move the job,sometimes you may not even have to touch the opposing jaw.

DO NOT TRY AND SET 2 JAWS THEN THE OTHERS,you will have to work around the chuck ,1st two then the others,reset zero,check again,and so on untill its set to where you want it.

Dont worry if by some chance you cant get it to read zero all the way around,generally as long as the opposite jaws are showing the same reading it will be centred,same goes if you get 3 jaws showing the same and one is out,nothing you can do with that.

The only way to learn to do this is by practice.

[Bryan]

Over tightening the jaws was throwing me off when I started. You have to finesse them a bit.

[krisfarm]

Welder,
Have you seen this video, it makes it easy.
[ame="http://www.youtube.com/watch?v=2KMhx4DbyDg"]YouTube - ‪Easy centering 4 jaw chuck‬‏[/ame]
Bob

[welder]

well i did it the problem i had was i did not center it close enough before i used the indicator. but i did it in under 2 minutes thanks for the tips guys it really helped.