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    redlee's Avatar
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    Default finding the "Center of a chuck

    jaws.jpg How would you determine on a 4 jaw if the tongue on the jaws like in the pic, are on center with the body of the chuck . We want to make a simple fixture using a 4 jaw chuck but need to know if the jaws are on center with the body , is there an easy way without setting it up on say a Boring mill table and dialing it all in. Someone Im sure knows a quick or easier way. Also need to know if its running the same through out its travel in the chuck body. Thanks

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    CalG is offline Titanium
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    shove a mandral through, mount the CHUCK between centers, Indicate on the chuck body, adjust the jaws to your heart's content,

    Viola!

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    redlee's Avatar
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    Quote Originally Posted by CalG View Post
    shove a mandral through, mount the CHUCK between centers, Indicate on the chuck body, adjust the jaws to your heart's content,

    Viola!
    Not sure what you mean by shoveing a mandrel? ? We need to know if the jaws are on center of the body ,Laterally.

  4. #4
    AA+
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    Would this work?
    -1- place chuck normally on lathe, remove jaws.
    -2- attaching dial indicator to carriage rotate chuck to level the chuck ways for the jaws, note reading.
    -3- rotate chuck 180 degrees, level again, note dial indicator reading. Discrepancy is 2x amount of ways off center.

    Best wishes --- Allen

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    redlee's Avatar
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    Quote Originally Posted by AA+ View Post
    Would this work?
    -1- place chuck normally on lathe, remove jaws.
    -2- attaching dial indicator to carriage rotate chuck to level the chuck ways for the jaws, note reading.
    -3- rotate chuck 180 degrees, level again, note dial indicator reading. Discrepancy is 2x amount of ways off center.

    Best wishes --- Allen
    Good one,- but how do you hold the chuck in position? its on a CNC and the chuck always seems to move a little when you release your hand.

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    Quote Originally Posted by redlee View Post
    Good one,- but how do you hold the chuck in position? its on a CNC and the chuck always seems to move a little when you release your hand.
    make sure your in low gear...may help the free wheel.

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    IT may be a moot point if you always use the same chuck on the same machine, but measuring the chuck on the lathe spindle measures the mounted lateral deviation of the combination of the chuck and the spindle. If you are trying to analyze the chuck alone, you need a different method. If you have a D1 Camlock, you could use the "mounted" method, but switch the orientation of the chuck 60 in sequence. If you get the same runout at the same point on the chuck each time, you've got chuck runout. If putting the chuck pins in different holes give you different values of runout, you need to do some figuring to determine which runout is the spindle and mount, and which runout is the chuck.

    The mandrel referred to above is a rod that has accurate center-drilled holes on each end. I think you'd put the rod into the chuck on the lathe, center it well, then remove the lathe and rod together, and chuck one end of the rod in a indexing head. Then you can set up the index head to get one jaw parallel with your surface plate (you are working on a surface plate, right), and measure the top and bottom height (near the center, and at the periphery both). Rotate four times to get another eight measurements. Then measure under the jaw - same thing with inner and outer measurements. Then move your surface gage with your indicator to the other side of the chuck and repeat.

    You'll then get to do a boatload of calcs to ensure that the jaws are central. Anyway, that's what a mandrel is. A rod with end holes. A very precise rod with end holes. In fact, you may want to avoid standard mandrels (which have a small taper). You could create your own with TG&P rod.

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    redlee's Avatar
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    Quote Originally Posted by bosleyjr View Post
    IT may be a moot point if you always use the same chuck on the same machine, but measuring the chuck on the lathe spindle measures the mounted lateral deviation of the combination of the chuck and the spindle. If you are trying to analyze the chuck alone, you need a different method. If you have a D1 Camlock, you could use the "mounted" method, but switch the orientation of the chuck 60 in sequence. If you get the same runout at the same point on the chuck each time, you've got chuck runout. If putting the chuck pins in different holes give you different values of runout, you need to do some figuring to determine which runout is the spindle and mount, and which runout is the chuck.

    The mandrel referred to above is a rod that has accurate center-drilled holes on each end. I think you'd put the rod into the chuck on the lathe, center it well, then remove the lathe and rod together, and chuck one end of the rod in a indexing head. Then you can set up the index head to get one jaw parallel with your surface plate (you are working on a surface plate, right), and measure the top and bottom height (near the center, and at the periphery both). Rotate four times to get another eight measurements. Then measure under the jaw - same thing with inner and outer measurements. Then move your surface gage with your indicator to the other side of the chuck and repeat.

    You'll then get to do a boatload of calcs to ensure that the jaws are central. Anyway, that's what a mandrel is. A rod with end holes. A very precise rod with end holes. In fact, you may want to avoid standard mandrels (which have a small taper). You could create your own with TG&P rod.
    We have expansion mandrels here just was not clear on what he was talking about, its a 24" 4 jaw a little to big I think for a 4" mandrel, but I think I get the idea now thanks.
    The chuck is a direct or bolted on mount with a location "Button"

  9. #9
    CalG is offline Titanium
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    Red

    I remain a bit confused by what you are trying to acertain

    Your statement "need to know if the jaws are on center with the body" does not convey all the variations I might imagine.

    Do you suspect that the jaw slide ways have been mismachined? That would be a job for a CMM ;-)

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    Take the chuck on or off the machine, off would be easier, remove jaws, place ground straight bar across grooves of the jaws, take square to straight bar and see if 90 to first bar. Since the jaws and chuck have been wearing since day one of their use, you likely should be happy with .003 difference in square, althought a 24" chuck might be a bunch more, there is play in the jaw to chuck fit as well.

    Second idea place on mill table put DTI in quill, mark one jaw as reference, get that jaw groove straight in one axis. Now center with an edge finder, and measure each groove to the first,you can then see how far out each jaw groove is the the first.

    This is a bit of a fools errand, IMHO

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    redlee's Avatar
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    img_0304.jpgimg_0303.jpg
    Quote Originally Posted by CalG View Post
    Red

    I remain a bit confused by what you are trying to acertain

    Your statement "need to know if the jaws are on center with the body" does not convey all the variations I might imagine.

    Do you suspect that the jaw slide ways have been mismachined? That would be a job for a CMM ;-)
    Yes this may help, the soft jaws are machined with offset holes for different discs, the holes in the disc do not go all the way through, and are offset .04, some are .03 , .06.
    The profiles on the discs are not on the shaft centerline so are difficult to check, without a CMM.

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    Aren't those cute! Little baby disks. We used to make by the truckload. All the small ones are made by the C.H. Ina or the K.O. Rea company now.
    Now, we just do the big ugly ones.
    JR

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    Quote Originally Posted by JRIowa View Post
    Aren't those cute! Little baby disks. We used to make by the truckload. All the small ones are made by the C.H. Ina or the K.O. Rea company now.
    Now, we just do the big ugly ones.
    JR
    We do up to 36" also but on a different machine of course.

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    Unless it's Inconel, Monel, or some weird alloy, we start at 24" and go to 72". We used to sell some 84", but haven't seen any in 10 years.
    JR

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