I realise people shy away from four jaw chucks, mostly because of the time it takes to centre the workpiece properly. But it needn't take much effort at all and you can do better than most three jaws quite easily.
I'm not trying to teach anyone to suck eggs, just showing how I do it. Tips, suggestions or corrections welcome as ever
![:ddb:](https://madmodder.net/Smileys/default/dancenana.gif)
First I fit the workpeice by eye and then spin it noting movement against a fixed point. Usually a tool in the QCTP. Nothing too exact, just close by eye.
Then I fit a dial gauge to the toolpost. Select an opposing pair of jaws, lets say jaws one and three, and zero the dial gauge.
![](http://i401.photobucket.com/albums/pp92/thebodger/Lathe%20Work/Centering%20the%204%20Jaw/IMG_3624.jpg)
Rotate the chuck to line up jaw No3 and note the reading. In this case 34 thou
![](http://i401.photobucket.com/albums/pp92/thebodger/Lathe%20Work/Centering%20the%204%20Jaw/IMG_3625.jpg)
Divide the 34 by 2 = 17. Turn dial so that the halfway point (17) is on the needle
![](http://i401.photobucket.com/albums/pp92/thebodger/Lathe%20Work/Centering%20the%204%20Jaw/IMG_3626.jpg)
Now adjust jaws 1&3 until the needle points to zero on the dial.
![](http://i401.photobucket.com/albums/pp92/thebodger/Lathe%20Work/Centering%20the%204%20Jaw/IMG_3627.jpg)
That's it, if you spin the chuck to indicate jaw No3 it will also read zero. Now repeat for jaws 2&4.
It takes a lot longer to write this than to do the job, but once you have got your head around it you'll find centring the four jaw quite easy and much more accurate than the 3 jaw.