Chuck wobble issues/questions
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  1. #1
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    Default Chuck wobble issues/questions

    How can i fix this chuck wobble ?

    Shared album - Keith Benoit - Google Photos

    Its a union 5" 3 jaw. I saw it run on the lathe i got it from and it ran true on that lathe and cut beautifully.

    I have cleaned the threads on both spindle and chuck. I measured 0.017-0.018" of wobble on the front face.

    I am getting 0.002" lift on the front spindle bearing when i do the deflection test.

    I have 2 other chucks, 5" 3 jaw cushman (jaws trashed) and 6" 4 jaw that the bodies run true on my spindle. Also collets run true

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    It looks like it's not threaded all the way on to the shoulder of the spindle nose. Are the threads bottoming out in the back plate before it goes on far enough?

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    I would not expect the face to be true swapping from one lathe to another. Theoretically it should, or be close, but exactly how it sits on shoulder to where on thread usually makes a little difference. The amount of wobble seems excessive though.

    First, you said you cleaned threads on both, so I'm assuming you are bottoming snug on shoulder ?

    Have you done any checks to see if spindle is true or bent ? Watching the vid, I'd guess spindle is bent. I'm not very familiar with that size lathe. If there is an internal taper in spindle, you can get a test bar to check.

    Whether the spindle is fine or not, I would do the following if chuck can be unbolted from back plate:

    Remove chuck from back plate. Screw back plate on to spindle. Run a facing cut on back plate till true. Bolt chuck back on.

    Or optionally buy a semi machined back plate. Face, and otherwise fit it to chuck.

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    Quote Originally Posted by Derek Smalls View Post
    It looks like it's not threaded all the way on to the shoulder of the spindle nose. Are the threads bottoming out in the back plate before it goes on far enough?
    I agree in the video it does not appear to bottom out. I will investigate further when i get home.


    Quote Originally Posted by texasgunsmith View Post
    I would not expect the face to be true swapping from one lathe to another. Theoretically it should, or be close, but exactly how it sits on shoulder to where on thread usually makes a little difference. The amount of wobble seems excessive though.

    First, you said you cleaned threads on both, so I'm assuming you are bottoming snug on shoulder ?

    Have you done any checks to see if spindle is true or bent ? Watching the vid, I'd guess spindle is bent. I'm not very familiar with that size lathe. If there is an internal taper in spindle, you can get a test bar to check.

    Whether the spindle is fine or not, I would do the following if chuck can be unbolted from back plate:

    Remove chuck from back plate. Screw back plate on to spindle. Run a facing cut on back plate till true. Bolt chuck back on.

    Or optionally buy a semi machined back plate. Face, and otherwise fit it to chuck.
    The spindle runs true with other chucks I have and with collets. The jaws on the other chuck i have are trashed hence me trying to use this chuck.

    From the video it does not appear to be bottoming out on the shoulder, i will investigate later when i get home.

    The chuck has a intergral back plate, it cant be removed/faced. That was my first thought but cant be done.

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    It definitely is NOT fully seated. I suspect because the chuck mounting plate is fully threaded, while a SB mounting plate requires a 0.362" opening of 2.335" in the back. If you look at the first "F" in this pic, you'll see that the thread is only 15/16" long, with a 2.25" shelf in the back. The plate has to duplicate these dimensions.

    sb-tooling-dimensions.jpg

    If you can't remove the plate, then the entire chuck will have to be mounted and the recess turned into the chuck. You should be able to do this with your 6" chuck.

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    yes,to above.

    BUT runnung that lathe without oil cups or at least a plug in the hole is a recipe for disaster....one little piece of debris falls in that hole and siezes the spindle at speed......think about it....whats that chuck gonna do?

    last thing i am is a safety nanny....but thats a major hazard.

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    Good catch on the oil cups, they are on order from mcmaster. I should hopefully have them tomorrow actually. I also ordered some felting and the needle bearings for the takeup.

    I haven't really used the lathe for much yet. Still trying to get it up and running and situated. Need to adjust the spindle clearance also and put a felt on the front bearing for the spindle still

    I think i found my problem. As discussed earlier the chuck was not seated all of the way. I am measuring 1.5105 on the spindle dimension "G" on my lathe and the ID of the chuck is measuring 1.5015 so 0.009" off. I am going to check with the guy i got it from to see if he can measure his spindle.

    I should be able to put the back side of the chuck in my 4 jaw and bore that out slightly right ?
    Attached Thumbnails Attached Thumbnails 20200114_190528.jpg   20200114_190341.jpg   20200114_190550.jpg  

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    Quote Originally Posted by KBenoit1 View Post
    I should be able to put the back side of the chuck in my 4 jaw and bore that out slightly right ?
    I would remove the jaws and mount the chuck and turn the shelf to 1.580" or so, with a depth of 0.200".

    A question: How do you remove the scroll from the chuck? Or, how did the scroll get IN the chuck?

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    its a split chuck. the backing plate is the rear part of the chuck. there is no separate mounting plate that bolts to it. the chuck is still screwed together and separates but the 1 1/2-8 threads are forever part of it.

    (yes i know it needs to be cleaned, trying to make sure i can get it to spin true first)
    Attached Thumbnails Attached Thumbnails 20200114_221301.jpg   20200114_191629.jpg  

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    I wanted to follow up on this thread since it seems to many times threads like this never get a resolution.

    I bored the chuck out to 1.525" which was the Id measured on my other chucks. The chuck now screws on all of the way and seats on the spindle. There is no more wobble.

    I also while doing all of this ended up pulling my spindle, put in the missing felts from the headstock, endless serpentine belt, added Gits cups to the top of the head stock, added the thrust bearing for the take up and set spindle clearance to .0015". What a difference the rubber belt makes, it cuts like a actual lathe now!

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