Just found out my chuck doesn't fit my spindle!
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  1. #1
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    Default Just found out my chuck doesn't fit my spindle!

    Boy am I bummed. When I found my lathe I was so happy it had a 2 chucks with it. A 10" 4 jaw Skinner and a 9" 3 jaw Skinner that looked very clean. The 4 jaw was on it when I brought it home and it wasnt until I just spent 6 hours cleaning up the 3 jaw that I found it is too large for my spindle! It's a 2 1/2" diameter. I was going to use the three jaw for a while since it's lighter and easier to manage while I get started with this thing. That 4 jaw is a monster with a welded seam thick backplate on it! I like the simplicity of a three jaw. I guess I am just sharing my pain of the joys of vintage lathe ownership!

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    Chances are your three jaw has a removable backplate. Can always make a new one, not that you have a lathe

    As others are likely note, there's lots to recommend a 4 jaw and once you get used to dialing it in you might even prefer it even for most ordinary turning.

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    About 20 years ago I bought both new four jaw and three jaw for the Monarch, same size. The three jaw still sits on the floor, never been on the lathe

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    Quote Originally Posted by PeteM View Post
    Chances are your three jaw has a removable backplate. Can always make a new one, not that you have a lathe

    As others are likely note, there's lots to recommend a 4 jaw and once you get used to dialing it in you might even prefer it even for most ordinary turning.
    No so lucky there, I think it has a "back plate" that can be removed but looks to me an integral part of the chuck. That looks above my skill set!


    p1050332.jpg

    p1050333.jpg

    p1050334.jpg

    p1050335.jpg

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    Quote Originally Posted by johnoder View Post
    About 20 years ago I bought both new four jaw and three jaw for the Monarch, same size. The three jaw still sits on the floor, never been on the lathe
    2 3/8" x 6 TPI??

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    take the chuck apart and you may find bolts on the inside holding the back-plate on.

    find or grind a close fitting screw driver and give the screws a good whack with a hammer before stripping the screws out.

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    front mount chuck??
    if so removing the 3 slotted screws on the jaw side of the chuck will allow removal of the backplate.

    if its 5 threads per inch chances are it a Leblond backplate.

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    Quote Originally Posted by Kevin T View Post
    2 3/8" x 6 TPI??
    new four jaw and three jaw for the Monarch, same size

    "same size" refers to OD of chuck (12") not thread (it isn't a threaded spindle)

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    Quote Originally Posted by johnoder View Post
    "same size" refers to OD of chuck (12") not thread (it isn't a threaded spindle)
    Ahhh! As it stands the 4 jaw I have wont hold any stock under about 1". I have been piece mealing a collet set and have all the collets I need under 1" but I still need to get or make a draw bar closer to use them.

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    Yeah, it's the three slotted screws holding on the back plate. Take them out and put in their place threaded rod (that matches their thread) as far as they can go and tap them in a sequence to slowly push out the back plate. It's likely to be a line-to-line fit, so the going will be slow.

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    Guessing you prolly saw it, but we just recently discussed back plates in jmdriller41's thread.

    A link to a back plate:
    8" Semi-Machined Threaded Back Plate 2-3/8"- 6 For All Plain Back Lathe Chuck | eBay

    One thing about these back plates, you can practice a little, and start over. They're pretty thick on face. So I wouldn't worry to much about mistakes, if you're figuring things out.

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    As others have stated, you have not identified the actual back plate.

    p1050332-backplate.jpg

    That is the actual back plate. Once it is removed you will find that it has a boss that fits a recess in the chuck itself. When you are buying chucks you purchase the chuck and the back plate and they should arrive separated (Exceptions do exist).

    You then put the back plate on the spindle and machine it to fit your lathe. This accomplishes two major things, first it means that the chuck is much more likely to have very little run out as you will be cutting the boss exactly for your lathe. To understand, just slap a piece of bar stock in a four jaw chuck and make sure it is not centered. Carefully turn it down. At some point you will have a "perfectly" round piece of stock that is exactly centered with your spindle. You are doing the same thing when you are creating the boss. You are creating a boss that is exactly centered with your spindle.) The second thing you accomplish is that you get to set the tolerances for what is acceptable to you.

    To remove the back plate you need to loosen the three screws on the face of the chuck p1050335-screws.jpg

    Once these three screws are removed it is only the fit between the boss on the back plate and the recess in the chuck that keeps them together. That should be a tight fit. Using threaded rod or sacrificial bolts or screws you can screw them as deep as they will go and then tap them gently, in sequence to drive the back plate off.

    Next step is to purchase a back plate from a source that already has the right size spindle mount.

    If you do not want to purchase such a back plate, you'll need to purchase some stock to make it from scratch:
    1) Mount stock in four jaw chuck.
    2) Drill and bore to size.
    3) Internal thread correctly. (Fitting can be an issue. You might have to dismount your four jaw chuck from the spindle without taking the new back plate out, turn it round and see if it fits on your spindle.
    4) Create the mating surface in the bore to match your spindle. This is what will align your new back plate with the spindle. The threads hold the back plate to the spindle, the mating surface is what puts the back plate in the right position.
    5) Verify that everything fits, remove four jaw from spindle, turn it around, screw the new back plate onto the spindle. Make sure there is NO sloop. If sloop, start over.
    6) Carefully remove the new back plate from the four jaw. Do NOT let the four jaw fall on your ways. Take the new back plate off the spindle with the four jaw and then take the new back plate out of the four jaw.
    7) True the outside of the back plate, just because it makes pretty and is easy.
    8) Machine boss in new back plate. Make sure it is a tight fit to the recess in the three jaw chuck.
    9) Use transfer punches to mark the locations of the three threaded holes you will need to hold the three jaw chuck to the back plate.
    10) Remove new back plate from spindle. Drill and tap the three holes.
    11) Attach the three jaw chuck to the newly manufactured back plate.

    Enjoy high fives and a beer or good cocktail, you've done something cool.

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    Thanks again guys I would not have known how to get that thing apart! I soaked the three bolts overnight in PB Blaster and got them out. Very stubborn! Next off to the hardare store to get some long bolts or threaded rod

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    Make an adapter with the inside threads that fit your spindle and outside threads that mach your backplate.

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    Quote Originally Posted by garyphansen View Post
    Make an adapter with the inside threads that fit your spindle and outside threads that mach your backplate.
    This is what I did when I recently made some spindle nose protectors for Heavy 10s. You have to make it as near identical to your spindle as you can! This will mean many measurements over wires as you progress. Making a measurement over wires is a royal PITA for a person with only two hands, but it must be mastered to successfully construct your thread "gauge".

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    Quote Originally Posted by texasgunsmith View Post
    Guessing you prolly saw it, but we just recently discussed back plates in jmdriller41's thread.

    A link to a back plate:
    8" Semi-Machined Threaded Back Plate 2-3/8"- 6 For All Plain Back Lathe Chuck | eBay

    One thing about these back plates, you can practice a little, and start over. They're pretty thick on face. So I wouldn't worry to much about mistakes, if you're figuring things out.
    This looks like the way to go, only the 8" is a little too thin everywhere else but they have a 10" for 20 bucks more that looks like a better match. The only trouble is their default shipping shows 159 bucks to my house! I sent an email to them asking if they can put it in a flat rate box. Hopefully they can because that will only cost about 25. Fingers crossed...

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    Quote Originally Posted by garyphansen View Post
    Make an adapter with the inside threads that fit your spindle and outside threads that mach your backplate.
    That would be really delicate work. The chuck is 2 1/2-6 and my spindle is 2 3/8-6!

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    If you buy a 3 jaw chuck get one with the removable top jaws. As far as that goes you can always hold a smaller 3 jaw in the 4 jaw.

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    Good news the guys at Discount Machine Shop on Ebay will ship it in a flat rate box for 21 bucks! And I started cleaning up that 4 jaw. It's really a nice looking chuck I am just not all that familiar with using a 4 jaw. Plan is to get it cleaned up and do some checkouts on it to see how good it is while I wait for that back plate.

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    "The chuck is 2 1/2-6 and my spindle is 2 3/8-6!"

    Still no problem, just more work. Bore out the threads of the back plate to a larger size and re-thread. Make the adapter accordingly. Some people mistakenly think the threads should be a close fit. That is not needed.


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