# How To Center Work In A 4 Jaw Chuck



## HMF (Nov 3, 2015)

One man's way....

*Centering Work in the Four Jaw Chuck - One Guy's Way*

To easily center work in the 4J, you'll need to make yourself two tools. First, make a dedicated holder of some sort so you can mount a dial indicator (DI) on the tool post (or directly to the compound) with its axis perpendicular to the spindle axis.  Adjust the DI so its plunger is vertically aligned with the spindle axis.  An easy way to do this is to put a pointed tip on the DI plunger and align the point to a dead center in the headstock.  The idea is to make something that you can drop into place, already aligned, and lock down in ten seconds or so.  Leave the DI permanently mounted to this holder.  A cheap import DI (<$15) is fine since we'll be using this only for comparative, not absolute, measurement.

While you could use a conventional adjustable magnetic DI holder, I strongly recommend that you make a dedicated mount that is easily installed and removed. A general maxim of machining is that you'll be much more likely to do something 'the right way' if setting up to do it is quick and simple.  If it isn't you're much more likely to try some half-a$$ed setup that doesn't work and ends up damaging the tool, the work, or, worst of all, you.

The second tool to make is a clone of your 4J chuck wrench.  We're going to be adjusting two jaws at a time and it's infinitely easier to do if you can move both jaws in and out in concert without having to swap the wrench from hole to hole.  It's another example of the maxim I mentioned above.  The clone wrench doesn't have to be anything fancy.  Machine a square tenon to match the existing wrench on the end of some suitable stock, and drill for a press-fit cross bar.  Use your existing wrench as a guide for dimensions.  I've found that, if there's not a lot of room on the back side of the lathe, making the clone somewhat shorter than the supplied wrench is a good idea.

Ok, now for the procedure.  Mount the work in the 4J and roughly center - either by eye or by using the concentric circles scribed into the face of most 4Js.  Snug the jaws down so the work is held securely.  Turn the chuck so one jaw is at the nine o'clock position as seen looking from the tailstock down the spindle axis.  Use the cross-slide to bring the DI up against the work and reading about the middle of its range (e.g., about 0.5" on a 1" DI).  Turn the scale on the DI so its needle indicates zero.  Now swing the chuck through 180 degrees.  Unless you've got an impossibly good eye, the DI will now read something other than zero.  (For an example, let's say it reads 0.038.)  Turn the DI scale so the zero is halfway to this reading.  (Move the scale so the needle points to 0.019.)

Now, insert both chuck wrenches and adjust the jaws so the DI needle points to zero.  Swing the chuck 180 degrees and check the reading - it should be close to zero.

[Aside:  If the part you're centering has the same dimension in both jaw axes (i.e., it's not rectangular), the DI zero you established above will also be the zero for adjusting the other two jaws below - another advantage of this technique.]

Repeat this entire process for the two other jaws.  [What we're doing here is treating the 4J as two two-jaw chucks.  We can do this because the jaw pairs are orthogonal and, to first order, adjustments of one pair will have very little effect on the setting of the other pair.]

If you've been careful, the total runout on the part should now be only a few thou.  Depending on your esthetics and the part requirements, this may be good enough.  If not, repeat the entire process until the runout meets your needs. After centering, check to ensure that all the jaws are clamped down tightly. It's easy to leave one loose.  If you have (left one loose), you may need to rerun the centering procedure after you've tightened it.

With this procedure, you should be able to center something to +/-0.001" in ten minutes on your first try.  With not much practice, you can get that number down to one or two minutes.  Soon your three-jaw will be gathering dust.

One of the most common uses of the 4J is for drilling/boring offset holes in eccentrics (i.e. cam drivers for model engines).  In this case, you aren't centering the stock itself (as we were above) but rather need to center the location of the hole.

First centerdrill the location of the hole in the milling machine.  Mount the stock in the 4J and roughly center this centerdrilled hole.  [A fast way to do this is to use the pointy end of an edge finder held in the tailstock drill chuck.]  Now you need a PUMP CENTER.  This is a longish rod (mine is ~10" long).  At the tailstock end is a spring-loaded female center.  At the headstock end is a rigid male center.  The male center goes in your centerdrilled hole.  The female center is supported by a dead center in the tailstock and the tailstock is adjusted to lightly compress the spring.  The DI is made to bear on the rod near the male center.  Using the procedure outlined above, adjust the jaws until the DI shows little or no runout.  Voila, the location of the offset hole is now centered.


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## HMF (Nov 3, 2015)

*Truing Round Work in the Taig 1030 4 Jaw Independent Chuck*
The Taig 1030 4 Jaw independent chuck is a versatile and strong accessory. I generally prefer to use it for round work over the 1050 3 jaw chuck as it grips strongly, and the work can be trued to almost no runout in a few minutes. Truing work in the 4 jaw chuck can be daunting to the novice however, as it requires the use of a dial indicator to true the work. Here are some pictures and notes about the process of chucking round work in the 4 jaw chuck.I may add more details on truing other work if people want.

*Back to Nick Carter's Taig Lathe Pages.*



The 4 jaw chuck. We want to true work by pairs of jaws. Get the work centered as close as possible by eye. Use the rings scribed on the face of the chuck as a guide.

If we loosen jaw #3 and tighten jaw #1, The work (the red circle) will move to the right. If we loosen jaw #1 and tighten jaw #3, then the work will move to the left.

Always loosen one jaw before tightening the other jaw.



A dial indicator. When the tip of the plunger is rested on the work in line with one of the jaws, the dial set to zero, then you can rotate the chuck 180 degrees and see which way the pointer moves, and how much. You want to adjust each jaw half of the pointer movement, in stages. Take it slow and check the indicator often, as it is your friend!

Tightening the screw on the jaw bearing on the side of the work the indicator plunger is bearing on will cause the pointer to move CCW, after loosening the opposite jaw.

Loosening the screw on the jaw bearing on the side of the work the indicator plunger is bearing on, and tightening the screw on the other side, will move the pointer CW

Always view the dial square on, so you don't make an error.



	

		
			
		

		
	
 The chuck opened up to accept the work


	

		
			
		

		
	
 A 1" bar chucked and roughly aligned by eye.


	

		
			
		

		
	
 How I use an indicator on the lathe. It is a bit more cumbersome to measure from the top, as the opposite screw is harder to access but I prefer to look at the top of the taig due to it's height. I made the indicator holder and it is always mounted and ready to use.


	

		
			
		

		
	
 Using a typical large magnetic base.


	

		
			
		

		
	
 A small test indicator magnetic base. You can also use the toolpost to hold an indicator. A test indicator will usually give a more accurate result but allows less leeway in setting up as the range is smaller (as is the dial) You can get it close with a .001 indicator then switch to a .0005 or even a .0001 if you are feeling somewhat crazy.


	

		
			
		

		
	
 Indicator at Jaw #1, the dial has been turned so the pointer is at zero. Indicators are relative, rather than absolute measuring instruments, so don't be afraid to rotate the dial.


The opposite jaw reading (remember it was set to zero on jaw 1) showing the runout is about .045"

Sorry about the poor quality of the pictures, I got too much shine from the dial indicator crystal.



	

		
			
		

		
	
 Rotated back to #1, I loosen the jaw a tiny bit


	

		
			
		

		
	
 rotated back to #3 and the jaw is screwed in, moving the work away from that side, and causing the pointer to move CCW (about .038")


	

		
			
		

		
	
 #1 is now at about .011, so we have runout now of .038-.011 or about .027 runout. Getting better. Loosening the screw on #1 again a bit


	

		
			
		

		
	
 Tightening the screw on #3 now moves the pointer to about .022"


	

		
			
		

		
	
 And #1 is now reading about .024" I have overcompensated a tiny bit, but the runout is now about .002"


	

		
			
		

		
	
 One more adjustment (loosening #3 and tightening #1) and I get the #1 jaw to read .023"


	

		
			
		

		
	
 Which means the #3 jaw also reads .023" Don't be afraid to rezero the dial if you start forgetting where each jaw is - it can be convenient to always make jaw #1 zero.


	

		
			
		

		
	
 rezeroing the #1 jaw


and rotating around #3 is also at zero.The work is now true between #1 and #3. You now repeat the process for jaws #2 and #4, then recheck #1 and #3 in case you threw everything off a bit.

Remember that round stock is rarely round, and sometimes not that straight, so try and true it at an average point.

Believe it or not, it only took me the few iterations above to true the work. Sometimes it takes longer, especially when trying to get to .0005 or less runout. You can use the same technique to indicate a bore true, using a test indicator or hole attachment.


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## Tony Wells (Nov 3, 2015)

I see one problem with that method, overall. He never indicates the face of the part. If you don't do that, yes, you can make one point along the diameter read pretty close (but it won't present a "round") but the rest of the piece will run out, hourglass style. You have to make sure the face is true at some point, probably when you get the axial runout within 0.010 or so. Of course, this doesn't apply to a rough, saw cut piece. In that case, if it is very long, you'll have to pick a spot near the chuck for indicating, then move out to the end and smack it around a bit until it is true enough for your purpose. Indicator if necessary, but don't smack your indicator.


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## HMF (Nov 3, 2015)

Tony Wells said:


> I see one problem with that method, overall. He never indicates the face of the part. If you don't do that, yes, you can make one point along the diameter read pretty close (but it won't present a "round") but the rest of the piece will run out, hourglass style. You have to make sure the face is true at some point, probably when you get the axial runout within 0.010 or so. Of course, this doesn't apply to a rough, saw cut piece. In that case, if it is very long, you'll have to pick a spot near the chuck for indicating, then move out to the end and smack it around a bit until it is true enough for your purpose. Indicator if necessary, but don't smack your indicator.



Whose method are you referring to? I left this thread open so there could be comments.


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## Tony Wells (Nov 3, 2015)

I was typing before you put up post #2. Obviously, a longer piece like in example 2 would eliminate the need to face indicate, but necessitate the 2 point method.  You won't find many, if any, 4 jaw chucks that will hold the stock perfectly straight hanging out that far.


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## HMF (Nov 3, 2015)

So #1 is incorrect....I can remove it. So ironic whose method it is.


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## Tony Wells (Nov 3, 2015)

No, not incorrect in entirety, just missing a key step, especially with the short part in the photos. One of the very first things I was tasked with as a new hire kid was getting a round fixture to run true in a 4 jaw. Was an old LeBlond as I recall. The fixture was about 14" diameter, and 10" long. It had to run true all around. I would never have gotten it without making sure the face was running true before indicating the OD. Actually, because of loosening and tightening as I indicated the diameter, I had to recheck and knock the face around during the process. In the end, I had it running in both planes within 0.0005 and the boss was happy. I think it was some sort of test.


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## mksj (Nov 3, 2015)

Nice post, thank you for your detailed explanation.

I use a dial gauge with a flat crown tip that attaches to a tool post holder on me QCTP, so makes for very quick checking of TIR readings and has very little flex. Also allows you to check two or three points on the stock with no change in set-up. I use the (VFD low speed 5-10 RPM) jog function to check the final TIR, as turning by hand can cause small variations in TIR readings (at least on my machine).

On small diameter rod, I am not sure indicating the face is going to tell you much, but I have had occasions with some pieces not clamping true. If it is a longer piece, one can always check the TIR at two points (proximal and distal to the chuck) and see if the TIR +/- around a 0 point is the same. Larger shallower stock, I use removable spacers or parallels that are placed between the chuck and stock to align the piece parallel to the chuck face (assuming this is true). One last tweak with the 4 jaw if you need high precision, is after you use the two key to get the TIR to 0.001",  then tightens one jaw to get the final tension to push the piece closer to true. Usually I can dial it down to within a few a few ten thousandth, with the goal that I can machine to a final dimensions of 0.001".  I use a combination 4 jaw, so it scrolls to a repeatability of about 0.002", then tension one individual jaw adjustment to get the TIR close to 0. Makes for quick set-up on repeat pieces. Getting the correct (equal) tension on all 4 jaws is important to prevent a part from shifting when machining.


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## ch2co (Nov 3, 2015)

I'm still a real newbie at most of this stuff, but wouldn't indicating off the face of the part in the chuck be suggesting that the face was perpendicular to the rest of the part?? or did I miss something there. 

   I can remember the first time I used my 4 jaw chuck and must have spent 2 hours on trying to get it right, before finally deciding that I was in too deep and went online and found a Mr. Pete video on Youtube. I'm one of those who seldom reads the instructions first, even though I know better.  The next time took just a few minutes.  I still only use my 4 jaw for non cylendrical parts like square pieces and for parts too big for my current 3 jaw. I know that many/most machinists recommend them for all parts, due to their greater accuracy if properly aligned, but I still find them to be too much of a chore to set up as opposed to a simple 3 jaw. 

Chuck the grumpy old guy


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## HMF (Nov 3, 2015)




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## ogberi (Nov 3, 2015)

I pretty much stick with the 4 jaw.  I have dialed in workpieces so many times it only takes a minute, and i can generally stop my ocd  from causing me to chase zeroes too much.  I generally go for barely a wiggle on a .001 indicator, thumping longer workpieces to run true down their length.


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## British Steel (Nov 3, 2015)

Same as Ogberi, usually with a tenth DTI (finger clock, not plunger), or for small stuff it's collet time. For long workpieces the easiest is to dial in at the chuck, then adjust the fixed steady to size right at the chuck, slide it back to the far end and clamp down - a final check's a good idea, as if the work's off-centre in the steady it'll walk it out of the chuck jaws...


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