General Question

jtb51b

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Should I be able to turn the outside of a piece of stock round on both ends center drill the end away from the chuck and then remove it from a 3 jaw chuck and re-insert it without losing the center? This is on a Logan 200 lathe. I have attempted to adjust the 3 jaw chuck with a dead blow hammer and I cant get anywhere. As long as I start a piece and never remove it I can make fairly decent parts, if I ever remove the work and put it back in its over, it will be out ten thousandths or more!

Thanks for the insight,
Jason
 
The answer to your question is no. I do not understand what you think a center drill hole will accomplish(?)... If you have center holes on both ends, and support the work on centers that are true to the lathe axis, then you will not have runout, if done correctly.
 
The center hole isn't there for anything other than that's what the piece needs. A center hole.


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Unless the chuck is an adjustable type like some of those made by Buck, Pratt-Bernerd and others, the only thing that beating on it is going to accomplish is damage to it, the spindle and/or the spindle bearings.
 
Didn't beat on it. Just a few tTaps. I have enough sense not to destroy something if it doesn't want to move. So, if I put a work piece that is true in this 3 jaw chuck and it's off, what is the remedy? Jaw grinding? New chuck??


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Say I just need to open the center hole up larger in a bushing, how would I do that if the chuck is off? Hard to turn the center hole larger between centers.


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As long as the work is only chucked once and left there, the chuck will not enter into the equation and you will have surfaces true with the axis of your lathe. As soon as you take it out of the chuck, that concentricity is lost if you try to put it in the chuck again. Think ahead with your work flow, and plan to do all the work that needs to be accurate in one setup. It does not matter if the chuck is .020" out and wobbling around as well so long as you cut all surfaces that need to be true to each other in one setup.
 
Thanks bob. As long as I keep that in mind I guess I will be ok. Sure would be nice if the chuck were more accurate tho. Are there chucks that are accurate that are reasonably priced?


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Thanks bob. As long as I keep that in mind I guess I will be ok. Sure would be nice if the chuck were more accurate tho. Are there chucks that are accurate that are reasonably priced?


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There is more accurate, and more accurate yet, and even more accurate than that. Each increment of added chuck accuracy is due to luck or to $$$, sometimes both. All chucks will have runout, that is a fact of life. Good machinists make beautiful and accurate parts with poor tools. Study their methods and learn from them. Money does not necessarily buy success, knowledge and skill does...
 
OK. So the hole runs part or all of the way through the part and is not for a dead or live center. If your chuck has exactly 0.010" runout, and you drill a hole through the part, take the part out if the chuck, and put it back in at random, the hole will have between 0.000" and 0.010" runout, depending upon how close to exactly as it was in the chuck when you drilled the hole the part is when you put it back in. And assuming that the part is perfectly round.

If you turn the OD and drill the hole in one sitting, the hole and the OD should be concentric. For the time being until you sort the 3-jaw problem out, I would suggest that you use a 4-jaw.

EDIT:

If you hold the bushing in the chuck, however you enlarge the bore the ID is going to be off-center by the chuck runout.

To begin to fix the problem, I would start by removing the chuck and checking for runout on the spindle register. There shouldn't be any to speak of. If there is, and if it is consistent, either use a 4-jaw or a much more expensive adjustable 3-jaw. So long as it makes up on the spindle the same every time, the adjustable 3-jaw will compensate for spindle runout so long as the spindle isn't bent.

Another solution if the spindle taper has no significant runout and the bushing is small enough would be to use a collet.
 
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