# advice nedded



## Bab160 (Sep 16, 2012)

hi i have a lathe wm 240 china model and the 3 claw 125 mm comes with is not very precise and strikes by about 0.08 mm which I think is too much if I buy a new one from warco machines is there any chance that is less blur in or should I buy another brand if so, which?
 it may be possible to correct the old claw?

 bab


----------



## sssfox (Sep 16, 2012)

I think I understand what you are asking.

If the chuck has a separate backplate, it may be possible to turn it slightly smaller and offset the chuck to compensate for being off center.

I have seen where some people have installed setscrews in the chuck body that push against the edge of the backplate,making adjustment easier and repeatable.


----------



## Tin Falcon (Sep 16, 2012)

is it possible the jaws were improperly inserted they do need to inseteed in order. if the order is out or the jaws missed the scroll the first time around this will throw the jaws off center.  and like mr fox said it could be a mounting issue as well chuck up a piece put and indicator on it and measure the run out. 
unless the chuck is new and top quality there is almost always some run-out on a 3 jaw.
Tin


----------



## Bab160 (Sep 17, 2012)

Tin Falcon said:


> is it possible the jaws were improperly inserted they do need to inseteed in order. if the order is out or the jaws missed the scroll the first time around this will throw the jaws off center.  and like mr fox said it could be a mounting issue as well chuck up a piece put and indicator on it and measure the run out.
> unless the chuck is new and top quality there is almost always some run-out on a 3 jaw.
> Tin


 Tnx for the reply 
The jaws are inserted Right, and the run out on the main head is 0.00. 
When i Mount a straight Axel, from a small turbine , 100 procent straight it has run out on 0.08 mm.  so i Think maybe it the jaws has a slight differens in height. You Wright that there always, is some run out on 3 jaws  How dó you work with that.  you cant take out the part, and Mount it again with out being affected by the bad  run out   or Can you ?


----------



## skyline1 (Sep 17, 2012)

sssfox said:


> I think I understand what you are asking.
> 
> If the chuck has a separate backplate, it may be possible to turn it slightly smaller and offset the chuck to compensate for being off center.
> 
> I have seen where some people have installed setscrews in the chuck body that push against the edge of the backplate,making adjustment easier and repeatable.



This is a good idea I set mine like this by turning the back plate a few thou' undersize and clocking a bar held in the chuck then adjust the chuck against the backplate with the bolts just nipped up and tighten the bolts.

with older, worn chucks the eccentricity can vary with the jaw opening as some parts of the jaws and scroll are worn more than others.

0.08mm is about .003" in Imperial which isn't actually too bad. even new ones ere not that much better unless they are micro adjustable ones like "griptru's" and even then you have to clock and adjust them.

when removing and replacing parts in the three jaw I often mark the job and the end of one jaw with a felt tip pen so you can put it back in exactly the same position each time which helps a little. It is always a good idea to use the chuck key in all 3 holes when tightening this tends to equalise scroll wear a bit

The oldest trick, which is still often used is a very thin shim under one jaw fiddly but it works.

Regards Mark


----------



## Dr Jo (Sep 17, 2012)

Bab,

If you are looking for a high degree of accuracy (and the ability to withdraw and replacing work) then you should  be using a collet chuck, not a three jaw chuck. 

Warco will do a 5C collet chuck for your machine.

Jo


----------



## sssfox (Sep 17, 2012)

Bab160 said:


> Tnx for the reply
> The jaws are inserted Right, and the run out on the main head is 0.00.
> When i Mount a straight Axel, from a small turbine , 100 procent straight it has run out on 0.08 mm.  so i Think maybe it the jaws has a slight differens in height. You Wright that there always, is some run out on 3 jaws  How dó you work with that.  you cant take out the part, and Mount it again with out being affected by the bad  run out   or Can you ?



You shouldn't expect greater accuracy from a 3-jaw chuck.  As Dr Jo said, if you want repeatable accuracy, you need a good quality set of collet chucks.  The alternative is to use a 4-jaw chuck and dial it in every time.

With a worn 3-jaw chuck, the runout can vary with the diameter of the piece being turned.  Even if you get it to zero runout with one part, a different diameter part may still have runout.  

A 3-jaw chuck is usually used to get round stock close so it can be turned down to a smaller diameter.  0.08 mm runout is pretty good for a 3-jaw chuck.


----------



## Journeyman (Sep 17, 2012)

I have the WM250 which uses the same chuck. It might be worth trying it in one of the other positions ie without the stamped 0 lining up. I also found with mine that one jaw was slightly longer than the other two, a quick rub on a diamond hone reduced it enough to make the runout less. The jaws are flat ended not concave so rubbing one jaw will not affect the clamping efficiency. That said 0.08mm isn't too bad for a three jaw. Warco also do a nice ER25 collet chuck for the lathe.

Cheers, John


----------



## Brian Rupnow (Sep 17, 2012)

0.08mm is about .003". Thats about as good as you can expect from a 3 jaw chuck.


----------



## Dave Sohlstrom (Sep 17, 2012)

The other choice you have is replace it with a chuck that has two piece jaws and machine soft jaws for the job.

Dave


----------

