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PostPosted: Tue Jan 17, 2012 9:53 pm 
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All--

After spending over an hour trying to center a round work piece in a four-jaw chuck, I decided to get some online help. I found a simple routine using a dial indicator at littlemachineshop.com: Centering Work in a 4-Jaw Chuck.

Take a look at my results. I tried to refine it with a DTI, but either the procedure doesn't work for a bent indicator thingy, or I didn't implement it correctly. Probably the latter.

--Bill

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PostPosted: Tue Jan 17, 2012 10:07 pm 
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You are assuming that the jaw faces are true to the center line of the lathe. Very seldom to almost never are they true to the lathe center line. You need to chuck with copper or other soft metal and dial in near the chuck by moving the jaws. Once done the next step is to tap the tail stock end of the material in with a soft hammer or lead bar. Then repeat the process over as it may take several times to get it dialed in perfectly. With each try it gets closer until it runs perfect.

Richard W.


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PostPosted: Tue Jan 17, 2012 10:17 pm 
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Richard--

I do not quite understand. Does one follow this procedure every time the four-jaw is used? After tapping-in the tail stock end, if you have already tightened the jaws, how do you dial it in further?

EDIT: Oh, I think I get it. Tap it. Indicate it. Dial it in by working opposite jaws against each other. Repeat as necessary.

--Bill

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PostPosted: Tue Jan 17, 2012 10:47 pm 
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seal killer wrote:
Richard--

I do not quite understand. Does one follow this procedure every time the four-jaw is used?

--Bill


When you dial in near the chuck it runs true, but not at the tail stock end. Then when you tap the part on the tail stock end the part you dialed in near the chuck moves. Thus requireing it to be dialed in again. Once you have re dialed it in, then the tail stock end moves slightly, so it has to be tapped in again. Usually requires doing this 3 to 4 times or as many times it takes. That is why you chuck using soft metal so things can move with out damage to your part. The soft metal for chucking should only be about 1/2" wide, not the full length of the chuck jaw. As far as using the this method everytime you use the 4 jaw depends on part length and how close you need to be. This is where past experience comes in.

seal killer wrote:
After tapping-in the tail stock end, if you have already tightened the jaws, how do you dial it in further?--Bill


What you are doing is re-adjusting what has been tightened the first time. Meaning you may have to slightly loosen one jaw and tighten the other, but not so loose that the part falls. Only a few thousands at a time. It is one of those things you get a feel for.

I wish I knew how to post a video of the process.

Richard W.


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PostPosted: Tue Jan 17, 2012 10:49 pm 
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Bill you did the edit while I was typing an answer. I am glad you saw it before the reply.

Richard W.


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PostPosted: Tue Jan 17, 2012 11:01 pm 
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Richard--
Quote:
Bill you did the edit while I was typing an answer. I am glad you saw it before the reply.

Your explanation still helped a lot.

I have only just learned how to post videos to YouTube. I had to . . . first grandchild! :) It's very easy. First, establish a YouTube account. (Free.) Then, it is as simple as uploading a picture to this forum off your hard drive.

--Bill

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PostPosted: Wed Jan 18, 2012 5:53 am 
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this is how Ive learned to center in a 4 jaw.
http://www.youtube.com/watch?v=2KMhx4DbyDg
with the addition of a second key you can loosen one jaw while you take the extra room up with its opposite one.


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PostPosted: Wed Jan 18, 2012 9:27 am 
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sk1nner--

That is the same method as the one I found at littlemachineshop.com. However, the video you posted adds a second chuck key, which would be of great help!

Thanks!

--Bill

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PostPosted: Wed Jan 18, 2012 11:05 am 
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unless you are prepared to buy lots of dial test indicators do not!!! leave them in contact with the part being taped. they will be junk!!


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PostPosted: Wed Jan 18, 2012 1:13 pm 
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hammermill wrote:
unless you are prepared to buy lots of dial test indicators do not!!! leave them in contact with the part being taped. they will be junk!!


That is why I only use 1" travel indicators with a mag base. Mostly because you can get real good ones for $30 or less. To me the word "TEST" when applied to an indicator, means you are checking something. It makes me think of an inspection department. An indicator with .030 or .010" of travel isn't really meant for something that can run out .250 or more. Although I do use a test indicator with an indicol on a mill.


Also I crank the carriage out of the way when I dial in. I don't think I much care for the two chuck wrench idea, I have never done it that way. Mostly because I use 12" or larger chucks most of the time.


Richard W.


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PostPosted: Wed Jan 18, 2012 1:49 pm 
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sk1nner wrote:
this is how Ive learned to center in a 4 jaw.
http://www.youtube.com/watch?v=2KMhx4DbyDg


This movie leaves out dialing in the face first, then dialing in the OD.


Richard W.


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PostPosted: Wed Jan 18, 2012 3:03 pm 
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What kind of soft metal? Foil? A bent sheet of something?

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