does a wedge bar chuck have advantages on a manual lathe?
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  1. #1
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    Default does a wedge bar chuck have advantages on a manual lathe?

    while clearing out stuff in the shop i found a wedge bar 3 jaw chuck with two piece jaws in seemingly good order
    it would be the right size for my lathe and i have a backplate i could use.
    usually i have a big four jaw mounted, i have a scroll type 3 jaw chuck that is o.k. but i like the idea of two piece jaws
    does this type of chuck have advantages over a scroll chuck?

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    This is among the many things I've never heard of, I'd love to see a photo.

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    Quote Originally Posted by partsproduction View Post
    This is among the many things I've never heard of, I'd love to see a photo.
    They look similar to a regular scroll chuck however like a hydraulic they have limited clamping distance before needing to be reset on the next tooth or step. I am not sure what they excel at.

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    I think AlfaGT put one on a lathe, if you search for that you might find it. Seems to me they have advantages in accuracy (as well as being easier to power with a drawbar), but of course are less convienent than a scroll chuck.

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    I used a schunk roto-s wedge style 3 jaw for many years on a weiler cycle type cnc (toolroom/semi manual lathe)

    Absolutly loved this style chuck. Great repeatability and I believe due to the wedge moving so slowly per wrench advance it has a better multiplier of holding force per Lb the operator torqued. I'd cut pretty hard and never had parts move.

    Having 2pc jaws was great for tossing on different soft jaws, always repeated within 0.001"

    Super expensive chucks! But on that type lathe it paid for itself monthly doing shorpnpart runs and fast changeover

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    i guess will take it apart and check the innards
    if it is okay i will adapt the backplate and mount the chuck to see i it works out for me
    thanks for the replies

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    Quote Originally Posted by janvanruth View Post
    i guess will take it apart and check the innards
    if it is okay i will adapt the backplate and mount the chuck to see i it works out for me
    thanks for the replies
    Recommend you NOT take it apart. There's nothing you can "adjust" without specialized grinder and bespoke fixturing. Done as a regular service, that is - but the prices might buy several conventional scroll-operated 3-J chucks!

    Better to just grasp it in a larger 4-J, dial it in, "gently" check the grip and repeatability.

    If decent, THEN make a backplate and just use it if and when it suits your needs for repetitive working. "General purpose", wide range of sizes, is not really their long suit.

    2CW

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    Quote Originally Posted by thermite View Post
    Recommend you NOT take it apart. There's nothing you can "adjust" without specialized grinder and bespoke fixturing. Done as a regular service, that is - but the prices might buy several conventional scroll-operated 3-J chucks!

    Better to just grasp it in a larger 4-J, dial it in, "gently" check the grip and repeatability.

    If decent, THEN make a backplate and just use it if and when it suits your needs for repetitive working. "General purpose", wide range of sizes, is not really their long suit.

    2CW
    as i do not know where, when, how it came into my possession, and more importantly why the previous owner let it go, i will open it to see if it seems to be in order, clean and lubed before spinning 20 + kg of steel on a lathe at a thousand +rpm.
    as there are no adjustable parts inside it will just be a matter of finding and keeping the right order in disassembly and assembly.
    a running camera is helpful to find out, afterwards, where you screwed up...

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    Cleaning and lubricating is a good idea.
    Advantage to this style chuck:

    Grip! .................Closes tighter than scroll chuck.
    Speed of jaw change:................Can reverse master jaws from inside to outside in seconds.
    If you have extra master jaws, you can have them set with different top jaws ,...soft and hard. Change in seconds.

    More accurate:.........................;Geometry of the closing element (sliding plates) is constant unlike the scroll of a conventional chuck , therefore more repeatable.

    To see a graphic of the workings of these chucks look here:

    YouTube



    Down side:

    Must reset for different sized work.....Limited grip range. Most use a system of opening the jaws fully (within the range) then pushing a release button and opening or closing the jaws to the grip range needed...
    Only takes a few seconds...

    Have a 250mm Schunk on my Romi lathe and i love it! Won't go back to a plain scroll setup now, i am spoiled!
    Cheers Ross

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    Is there a NAME on the chuck? Like "FORKHARDT" or "ROHM"? They are precision chucks. They have the advantage of being able to be adjusted without cranking the key a lot. Look for a place on the face of the chuck where a small pin will come out if the safe range has bin exceeded. If the pin comes out the jaws have to be reset to the next position or the could be flying out at high RPM or not clamping at all. Crank the key to open
    the jaws. Pull the jaws out and than look inside. When turning the key you will see the "wedge" come into view. Now turn the key for the wedge to disappear and slide the jaws back in (Check for numbers on the jaws). You will feel (and hear)some "click". Bring the jaws close to the dia. you need on the click and than turn the key to engage the wedge. Watch for the PIN on the face of the chuck and make sure it is recessed into the face. Some chucks have dia markings on the face to make it easy to set the jaws. These chucks are much more precise and with more holding power than scroll chucks. That is why they are used mainly for hydraulic clamping. Takes a little practice but once you get used to it - it works just great. WATCH THE PIN,
    Click here:YouTube

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    I'm not sure what you have , but chucks with wedge style draw tube actuators are more for production set-ups . They are more limited in their range of motion but can be very accurate. There are hundreds of different designs for these type of chucks.

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    I agree with thermite. Do not take it apart. Since it seems your chuck is for manual operation just turn the key to open and pull out the jaws. Turn the key till you see the wedge. Clean it and lubricate. Turn the key till the wedge disappears and the "SAFE" pin appears. Re-insert the jaws - they can be set for inside or outside holding - to the same depth and turn the key for the wedge to engage and the "SAFE" pin to recess.
    Caution again: Do not operate the chuck if the "SAFE" pin is sticking out!!!!


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