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Old 12-13-2018, 06:02 PM
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Lu47Dan Lu47Dan is offline
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Default 4 jaw chucks, independent vs. scroll.. 8" or 10"

Thinking out loud it helps to clear the cobwebs.
I have for a long time wanted to purchase a 4 jaw chuck for the Clausing. But with the L00 mount used chucks were not plentiful around here or on the net. CDCO has one model, plain back, no mount, but they sell the mount also. It's main drawback is no rpm rating. So the search has drug on for a very longtime.
The other day I was searching for dividing head and stumbled on a 4 jaw chuck, 6",8",or 10" independent, with a semi-finished L00 mount . It has an rpm rating of 2100rpm. More than enough for me. Fitting the chuck to the mount is not that complicated, there have been several done here and there a more than a few series on Youtube showing the process. Most all my questions have been answered on that front.
The main question is what size to get?
I have a 8" 3 jaw on the lathe as the only workholding device right now.
Buying a 10" 4 jaw independent chuck id not too much more than the 8" 4 jaw independent is, but would the 10" be too big for my Clausing 6903 14" X 30" lathe?
The title of this thread says, independent vs. scroll....
I am going to buy one of each, the scroll has its uses, one of which is to drill into the end of square stock when dead nuts accuracy is not needed. I might have a production job of that nature, this coming spring. A 5C collet chuck will not work as the pieces are beyond the size range of the collets.
And the 4 jaw independent chuck will get a lot of use once I get started on the crawler again.
I am going to replace the 3 jaw also, but I would like to find a Set Tru or similar chuck to replace it with.
Any comments, ideas, or hard experience will help.
Dan.
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  #2  
Old 12-13-2018, 06:50 PM
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You could make your 3 jaw into a tru set and save buying another chuck.
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Old 12-13-2018, 07:24 PM
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I see no problem at all with the ten inch four jaw, I have a eight inch four jaw on my eleven inch lathe. As long as you can lift it I would go with the ten inch.IMO Nothing wrong with a extra inch or two
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Old 12-13-2018, 08:35 PM
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The hidden issue with chuck sizing is interference as you open the jaws. it is machine dependent.
I have that issue with one of my lathes where a 10 inch chuck will open wider than a 12 inch. a larger chuck is not automatically a better fit to a lathe.
Some things to consider are weight, opening clearance, how far out from the spindle bearing you are and clearance over the cross slide.
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Old 12-13-2018, 08:51 PM
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Quote:
Originally Posted by terry lingle View Post
The hidden issue with chuck sizing is interference as you open the jaws. it is machine dependent.
I have that issue with one of my lathes where a 10 inch chuck will open wider than a 12 inch. a larger chuck is not automatically a better fit to a lathe.
Some things to consider are weight, opening clearance, how far out from the spindle bearing you are and clearance over the cross slide.
Terry, I have thought of making circes to match the size of the various chucks I am looking at. I would use them to check clearances.
As to stick out from the front bearing, if I read the drawings correctly, the 4 jaw's weight is closer to the bearing than my current 3 jaws weight is.
Thanks.
Dan.
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  #6  
Old 12-13-2018, 09:25 PM
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Mac, the problem with 5C collet chuck for the production job, is the stock size, 2"+ square. I am not sure of the real size as I have not seen the prints yet. The last shop that did the job, messed it up to the point of about 1/3 of the run was scrap. The major tolerance bugaboo is length, + .002 / - .000. Hole is drilled than a form tool is run in to a certian depth. It is a goofy part, not too hard to make but finicky.
Another one of the no photos allowed jobs, I get once in awhile.
I could set up the job in the independent 4 jaw. It would be a little more work but it could be done.
Dan.
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  #7  
Old 12-14-2018, 07:24 AM
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Quote:
Originally Posted by terry lingle View Post
The hidden issue with chuck sizing is interference as you open the jaws. it is machine dependent.
I have that issue with one of my lathes where a 10 inch chuck will open wider than a 12 inch. a larger chuck is not automatically a better fit to a lathe.
Some things to consider are weight, opening clearance, how far out from the spindle bearing you are and clearance over the cross slide.
This is an issue to pay attention to. If you don't, and buy an oversized chuck, you end up with an extra heavy small chuck in reality.
I have a large 3 jaw that I almost always use, but I have a gap bed lathe and the gap gathers dust as I never put it back in. That way I can chuck something bigger than 4 inch without the jaws hitting the bed. It does not matter what size the lathe is, there will always be a chuck that causes interference with the bed if larger then needed.

The other notes about a set true are almost correct. A set true, once set for a specific diameter, is good for a range + or - the size you set. So if you had a shaft and zeroed the chuck and carved .250 off the far end, then flipped it end for end, you will still be on the money.
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  #8  
Old 12-14-2018, 10:53 AM
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If your still interested in a 4-jaw independent chuck, I have both a 8" and 10" Cushman, both with integral L-00 mounts here. The 8" was a NOS one I bought thinking I would use it on my used to own 13" lathe and never did. And the 10" one I bought new back in 1979 and has been used only a hand full of times over the years. If interested PM me. Ken
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  #9  
Old 12-13-2018, 08:44 PM
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You asked for opinions Dan, here's my .02

A 3-jaw chuck is a 3-jaw chuck, it will have "X" amount of runout, a set tru is a waste. If you keep the work in the 3-jaw chuck for all operations, then the part will be dead nuts true and concentric.

If you need to move the work between operations than you either need to turn it between centers or put it in an independent 4-jaw chuck and dial it in after each move. A 4-jaw scroll jaw chuck is useless as far as I'm concerned. If you have a production job to turn square or other than round material than a 5-C pot chuck or custom soft jaws in an 3-jaw scroll chuck would be my choice.

As far a chuck size goes, I look at it just like sizing a lathe or another machine. You can put small work in a big chuck but you can't put big work in a small chuck.
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  #10  
Old 12-13-2018, 09:10 PM
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Quote:
Originally Posted by rmack898 View Post
...A 3-jaw chuck is a 3-jaw chuck, it will have "X" amount of runout, a set tru is a waste. If you keep the work in the 3-jaw chuck for all operations, then the part will be dead nuts true and concentric...
I tend to agree about set-tru chucks. They're only good at the one point where you set them, otherwise you still have a 3-jaw chuck with it's inherent runout.

Having said that, as far as I'm concerned--for the work that we do--a 3-jaw is more than adequate for most things. I am constantly making parts in a 3-jaw and swapping them end for end to finish off--the few thou of runout that you pick up often doesn't matter.

If your lathe is capable of parting off efficiently an awful lots of parts can be made in a 3-jaw with most of the features concentric to each other. Often all you need to do after parting off is to face the "back" side which, in many different situations, doesn't need to be perfect in relationship the the rest of the part.

Quote:
...A 4-jaw scroll jaw chuck is useless as far as I'm concerned...
There aren't a lot of uses for 4-jaw scroll chucks but, like every other tool in the box, they do have their place. If you're machining round features on square stock they can be really handy--dialing square stock in on a 4-jaw is a pain in the ass.

As far as the size of your 4-jaw I think a 10" is just about the right size for a 14" lathe...
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