Scroll chuck accuracy.


john kling
 

The total run out of new scroll chucks frequently vary from < .0004 to .003 inches. The price also varies with accuracy.  To shore up my knowledge what are the differences in manufacturing procedures that are behind this range of accuracy?


Jim V
 

Ned, over on the Smithy Site recently bought a Shars chuck. It started out with about .004" runout. He did a bunch of tweeking on it, starting with taking it apart & cleaning the grit & crap out of it, adding 3 mounting screws from the front, modifing the cover diameter, adding 4 concentricity adjustment screws, lubing & reassembling it and came up with the following.........

This afternoon, I re-approached adjusting the SHARS lathe chuck concentricity starting with the lathe chuck mounting bolts initially set tighter.
Within a few minutes, I was able to adjust the lathe chuck run out to less than 0.001".
Within half an hour, the lathe chuck run out was adjusted to 0.0004" with the lathe chuck bolts fully tightened and measured with a 4-0-4 dial indicator (0.004" to 0.004") that has ten thousandths of an inch graduations.
As for work piece diameter concerns, the run out was adjusted to a 3/4" gage pin at 0.0004" and subsequently was 0.0008" with a 1/2" gage pin and was 0.002" with a 1" gage pin, all far less than the default run out of the chuck at 0.004".
Of course, for an important work piece the lathe chuck can be adjusted for run out at the diameter of the work piece.


On Wednesday, January 14, 2015 2:32 PM, "jkling222@... [SOUTHBENDLATHE]" wrote:


 
The total run out of new scroll chucks frequently vary from < .0004 to .003 inches. The price also varies with accuracy.  To shore up my knowledge what are the differences in manufacturing procedures that are behind this range of accuracy?



David Rysdam <david@...>
 

"Jim 'V' flajimak220@yahoo.com [SOUTHBENDLATHE]"
<SOUTHBENDLATHE@yahoogroups.com> writes:
Ned, over on the Smithy Site recently bought a Shars chuck. It started
out with about .004" runout. He did a bunch of tweeking on it,
starting with taking it apart & cleaning the grit & crap out of it,
adding 3 mounting screws from the front, modifing the cover diameter,
adding 4 concentricity adjustment screws, lubing & reassembling it and
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

There's the key right there. If you want your 3 jaw to be more accurate,
mount it in a 4 jaw.


Thomas G Brandl
 

Some 3-jaws come with adjusting screws, ie Buck_Adjust-True. From my POV, a 3-jaw is concentric at one diameter. Putting in another diameter part and it would be off x.xx amount concentrically. A 2-jaw should hold concentricity of 0.005 over its capacity. Some chucks may do better, or be reworked to do better. I think in some years ago post here someone did the work to bring their chuck from say 0.004-0.005 TRI down to 0.001 or such.

 

From: SOUTHBENDLATHE@... [mailto:SOUTHBENDLATHE@...]
Sent: Thursday, January 15, 2015 6:40 AM
To: Jim 'V' flajimak220@... [SOUTHBENDLATHE]; SOUTHBENDLATHE@...
Subject: Re: [SOUTHBENDLATHE] Scroll chuck accuracy.

 

 

"Jim 'V' flajimak220@... [SOUTHBENDLATHE]"
writes:
> Ned, over on the Smithy Site recently bought a Shars chuck. It started
> out with about .004" runout. He did a bunch of tweeking on it,
> starting with taking it apart & cleaning the grit & crap out of it,
> adding 3 mounting screws from the front, modifing the cover diameter,
> adding 4 concentricity adjustment screws, lubing & reassembling it and
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

There's the key right there. If you want your 3 jaw to be more accurate,
mount it in a 4 jaw.


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