Gallery, Projects and General > How to's

Cenerting the Four Jaw

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Darren:
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:


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.



Rotate the chuck to line up jaw No3 and note the reading. In this case 34 thou



Divide the 34 by 2 = 17. Turn dial so that the halfway point (17) is on the needle



Now adjust jaws 1&3 until the needle points to zero on the dial.


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.

Gerhard Olivier:
Nice write up Darren

I dont use the 4 jaw as much as I should because its big and scary :D

That would certainly save me a lot of time.

Gerhard

tinkerer:
 :nrocks: That sure does simplify it for me.  :smart: One day I will get some time in the shop and practice that. I bet you can use the same theory for off setting  point on the work also.

mklotz:
Your technique exactly matches what I wrote up for our metalworking club...

http://www.homemodelenginemachinist.com/index.php?topic=284.msg6405#msg6405 

One detail that I included is the advice to make a clone of your chuck wrench.  Since you'll be moving the two horizontal jaws in concert to zero the DI reading, it's far easier to have a wrench in each jaw to be adjusted than to constantly swap a single wrench between the two jaws.

Darren:
Ha, I promise you I hadn't seen that, I don't read that site.... no pictures to see  .....

like the idea of two chuck keys though, I'll copy that one ....  :thumbup:

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