Chuck help

[emasbury]

Hey Folks, I have a Craftsman/Atlas 12 X 36, the stand alone model, which has a 5 inch 3 jaw chuck that needs some serious help. I have decided to replace the chuck. My questions are as follows: I want a larger chuck, what is the largest size I can put one the lathe, 6 inch, 8 inch or larger? I'm going to be turning some soft stuff so should I get a 6 jaw chuck in whatever size I decide on, or just stay with the 3 jaw? Looking forward to your help and advice. So thanks in advance and I greatly appreciate any and all help you folks pass my way, Ed, Eagle River, Alaska.

 

[Pat of TN]

Looking through my Grizzly catalogue, it seems their (and a lot of other) 12" swing lathes come with 6" three-jaw and 8" four-jaw chucks. I would say either size would work, six or eight inches. What determines this is how far out the jaws can go before they hit the ways. On a 12" swing lathe, with an 8" chuck, the jaws would have to be out of the chuck by about two inches or more, theoretically, so I would say an eight-inch chuck would suffice, but no larger.I would also recommend you look into getting a four-jaw, independent chuck over a three-jaw scroll/universal chuck. A brand-new, quality three-jaw chuck can maybe repeat to a few thousandths' runout (.003 to .005 ish). Although a four-jaw does take more time since you must dial the part in to run true, the accuracy and TIR are limited only to the accuracy of your indicator and the time you wish to spend on it. A four-jaw chuck can also hold odd-shaped (IE square, octagon) pieces. Then again, you can adjust the runout of a three-jaw somewhat with a mallet and an indicator. If all you need is .005 TIR (or, runout that you can't see at a glance), a three-jaw is fine.I would also advise against a six-jaw chuck. A six-jaw chuck looks like a mean device, but they really don't provide a great difference in precision. They also require good, truly round stock to function well. If you work with a lot of tubing or pipe, a six jaw chuck also comes in handy due to the greater distribution of force.Sorry for the long-winded response, but there's a lot to choosing a chuck. Summary: I'd try an eight-inch chuck. A four-jaw independent chuck if you want or need the ability to turn square stock and/or less than .005 runout, or a three-jaw scroll chuck if you don't need sub-.005 runout and only mess with round stock...

 

[emasbury]

Looking through my Grizzly catalogue, it seems their (and a lot of other) 12" swing lathes come with 6" three-jaw and 8" four-jaw chucks. I would say either size would work, six or eight inches. What determines this is how far out the jaws can go before they hit the ways. On a 12" swing lathe, with an 8" chuck, the jaws would have to be out of the chuck by about two inches or more, theoretically, so I would say an eight-inch chuck would suffice, but no larger.I would also recommend you look into getting a four-jaw, independent chuck over a three-jaw scroll/universal chuck. A brand-new, quality three-jaw chuck can maybe repeat to a few thousandths' runout (.003 to .005 ish). Although a four-jaw does take more time since you must dial the part in to run true, the accuracy and TIR are limited only to the accuracy of your indicator and the time you wish to spend on it. A four-jaw chuck can also hold odd-shaped (IE square, octagon) pieces. Then again, you can adjust the runout of a three-jaw somewhat with a mallet and an indicator. If all you need is .005 TIR (or, runout that you can't see at a glance), a three-jaw is fine.I would also advise against a six-jaw chuck. A six-jaw chuck looks like a mean device, but they really don't provide a great difference in precision. They also require good, truly round stock to function well. If you work with a lot of tubing or pipe, a six jaw chuck also comes in handy due to the greater distribution of force.Sorry for the long-winded response, but there's a lot to choosing a chuck. Summary: I'd try an eight-inch chuck. A four-jaw independent chuck if you want or need the ability to turn square stock and/or less than .005 runout, or a three-jaw scroll chuck if you don't need sub-.005 runout and only mess with round stock...

Pat , Thanks for you advice, I was leaning toward the 8 inch 3 jaw and you pushed me over the edge. As for the 4 jaw I already have a fairly good one the serves me well. Thanks Again, Ed

 

[Ulma Doctor]

bigger is not always better,
most chucks have reverseable jaws for when you do larger diameter work.
you really don't wan't to put any more added weight to the spindle than is necessary.
but a 4 jaw chuck of even questionable quality can be dialed in, it may take more time to set up than a 3 jaw but you can get dead nutz

 

[Pat of TN]

Pat , Thanks for you advice, I was leaning toward the 8 inch 3 jaw and you pushed me over the edge. As for the 4 jaw I already have a fairly good one the serves me well. Thanks Again, Ed

Absolutely. Glad you have a four-jaw, to me a four-jaw independent should (almost) always be the first choice over a three-jaw scroll or even a collet chuck. Unfortunately my little 6x18 Craftsman only came with a three-jaw that's as old as the lathe is (at the least the mid-50s). Trust me, I share your agony in having a worn-out scroll chuck!

Ulma Doctor does bring up a good point, I might add. What I recommend is, purchase your chuck from a reputable company (assuming you buy new) and if you notice anything wrong or amiss, ask to return it. What I mean by 'wrong' is what I mentioned before, the jaws getting close to the ways when opened up somewhat, on top of Ulma Doctor's note about weight on the spindle. This would mainly become clear in the form of a more sluggish start-up; there may be other things as well but I can't think of any offhand.

One more thing - if you can, get a chuck with two-piece jaws. If you don't know, a two-piece jaw has a master jaw that rides the scroll and a top jaw that grips the part that is held on to the master jaw by cap screws. You can simply reverse these top jaws for holding large-diameter pieces rather than having a second set of jaws, and it also opens up a whole new world of workholding - soft jaws.

 

[emasbury]

Absolutely. Glad you have a four-jaw, to me a four-jaw independent should (almost) always be the first choice over a three-jaw scroll or even a collet chuck. Unfortunately my little 6x18 Craftsman only came with a three-jaw that's as old as the lathe is (at the least the mid-50s). Trust me, I share your agony in having a worn-out scroll chuck!

Ulma Doctor does bring up a good point, I might add. What I recommend is, purchase your chuck from a reputable company (assuming you buy new) and if you notice anything wrong or amiss, ask to return it. What I mean by 'wrong' is what I mentioned before, the jaws getting close to the ways when opened up somewhat, on top of Ulma Doctor's note about weight on the spindle. This would mainly become clear in the form of a more sluggish start-up; there may be other things as well but I can't think of any offhand.

One more thing - if you can, get a chuck with two-piece jaws. If you don't know, a two-piece jaw has a master jaw that rides the scroll and a top jaw that grips the part that is held on to the master jaw by cap screws. You can simply reverse these top jaws for holding large-diameter pieces rather than having a second set of jaws, and it also opens up a whole new world of workholding - soft jaws.

We must have the same old 3 jaw, mine has seen better days, can't wait to get a new chuck. Thanks guys.

 

[kd4gij]

Here is my lathe with an 8" chuck it serves me well.


I needed the 6" 4jaw for a quick project and was to lazy to change it :lmao:

 

[emasbury]

Here is my lathe with an 8" chuck it serves me well.
View attachment 79457

I needed the 6" 4jaw for a quick project and was to lazy to change it :lmao:

Now that would be something I would do.

 

[wa5cab]

Ed,

For relatively soft stock up to about 1" diameter, I would use collets (except for wood I would use centers). Above that you are stuck with chucks (unless you want to spend really big bucks). If you do a lot of the same diameters, a 6" 3-Jaw with two piece jaws and soft jaws might be a good choice. You can bore the bearing faces of the soft jaws to significantly spread out the clamping area. Just remember that you have to properly load the jaws outward (if gripping the OD of the workpiece) before you bore them.

Robert D.

 

[Mondo]

Here is my lathe with an 8" chuck it serves me well.
View attachment 79457

I needed the 6" 4jaw for a quick project and was to lazy to change it :lmao:

My, you ARE lazy! The problem with this is you cannot gain the major advantage oif the 4-jaw over the three-jaw, being the ability to center the work dead-on. The setup you have pictured will suffer from any TIR of the three-jaw no matter what you do to center the work in the four-jaw. A lazy setup, yes, brilliant, no. :nuts:
Really now, how difficult is it to thread the 3-jaw off and thread the 4-jaw on???

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To answer the original question of how big a chuck will fit, the answer is in how big a chuck is practical. An 8 inch diameter chuck is the limit of practicality on these lathes, be it a 3-jaw, 4-jaw, or 6-jaw. Anything bigger than 8" in diamater will be grossly excessive.

A 10" diameter 3-jaw chuck with an appropriate backplate will weigh about 60 to 80 lbs and will be gripping the work several inches out from the end of the spindle. This will amplify any TIR in the system and will detract from the accuracy oif the lathe.