aligning a four jaw chuck

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thomas harris
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aligning a four jaw chuck

Post by thomas harris » Sat Aug 04, 2007 4:03 pm

Ok, I now have a four jaw chuck with indepenently adjusted jaws. I like it so far, but have a question or two. I can get the run-out corrected near the chuck. Or at the end of the piece. What about getting it to do both? Is the chuck simply off or is it normal to need to jockey the work to get it aligned with the bed the whole length? The chuck is one of the original chucks that came with the atlas 618, (made in England 1x10" threads). It doesn't appear to worn, in fact it still has the origainal box with some old grease on the chuck itself. I'm using the inner jaws not the reversed ones for larger stock or pipe. Thanks in advance.

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Post by Fender » Sat Aug 04, 2007 5:40 pm

How long a piece are you trying to get centered? How much of a "wobble" are you trying to correct? Assuming that the wobble is fairly small and that the workpiece is longer than 3 or 4 diameters, you will need to support the end using a center in the tailstock.
What I would do is to chuck the piece in the four jaw with just a little of the right end sticking out, adjust the jaws to get it running truely, and then drill a hole in the right end with a center drill. If the diameter is too big for the hollow spindle, then use a steady rest to support it for drilling the right end. Now, chuck the left end in the 4 jaw, with a live center in the tailstock supporting the right end. Adjust the jaws to get the left end running true. After you have done this, you should be able to withdraw the tailstock and still have the piece running true along its length. Of course, you'll need the tailstock to support it when actually machining.
Dan Watson

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4-jaw alignment

Post by spro » Sat Aug 04, 2007 5:57 pm

i just happened to be here and will take an initial stab at your ques.I don't think there is anything wrong with the chuck. Hopefully there is nothing wrong with my response but it requires a knowlege of what plane is depended upon or referenced to be the accurate one. You mentioned the "inside jaws..not the outside for larger pipe etc." then that you can get the object to run square at the outside length. If this object/stock is already square to its length at the outside center is one thing and the tailstock center can be of much use by locating it while the chuck is adjusted.

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Post by Harold_V » Sat Aug 04, 2007 7:34 pm

What you're experiencing is very common with an independent four jaw chuck. Because two jaws can hold a piece relatively easily, if you tighten two opposing jaws then try to straighten the piece with the set that is 90° to the first set, they often won't overcome the original grip and won't straighten the part. It's a sure sign the chuck has good gripping power. Maybe too good! :)

Assuming you have no need for the center, as has already been well described, grip your part at the appropriate length, but just barely snug the four jaws equally, so the piece is free to move about when you tap the end. Adjust the chuck near trueness, then tap the outside (soft hammer) according to the high spot, then repeat the operation. You'll chase the piece a time or two until you get the hang of the operation, but it's not hard to master.

If squareness and center is important, you can use a DTI to run the length of the part to insure that it is parallel to the spindle. By this method, and some creativity, you can center a piece within tenths. The chuck should be able, so it's up to the operator to apply the proper procedure.

If you'd like more details on this operation, ask.


10 Wheeler Rob
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Re: 4 Jaw alignment

Post by 10 Wheeler Rob » Fri Aug 10, 2007 9:58 am

First question is was the back mounting plate for this 4 jaw taken of the chuck, mounted on your head stock and and checked to be running true.

Usually the mounting plate is face machined to insure the chuck is mounted perpendicular to your head stock. If the chuck is not moutned perpendicular, the jaws will not be parallel to the spindel.

That is why the cucks in machine shops are labled for the machine they were set up to run true on.

The other qusetion is what is the condition of the 4 Jaw and its jaws. Some have been abused, over thightend a lot or crashed, and make a better paper weight then anything else. I have one htat looks great, but works like crap, and an other the looks bet up, but works good. If its jsut the contacting surface of the jaw, then regind them. There was whole series of posts about how to do that on here in the past.

For a three jaw it needs to be made both concnetric and perpendicual


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