chuck balance

[speedyb]

Howdy, Installed a new 4" 3 jaw on my 7x16. no name chinese, from micromark. It seems to be a decent chuck, but there is a speed range in which it imparts a shudder to the lathe.
below and above it runs reasonably smooth. speed range where this happens is going to be used a bit I would think.

I am not experienced on measuring chuck paramaters, but so far I measure .003 runout measured against the side of the chuck body.
I will try one more position on the spindle, this is the second try.
And the faces of the jaws with them about halfway open, was very impressed at no measurable run out on a .0005 indicator. and the small bits of work held in it look good upon completion.

so should I be concerned ? its still new enough to send back , I think.
the original 3" chuck did not do this.

 

[steamer]

Hi Speedyb

.003" isn't a lot of run out...

concentricity seems good....can you anchor the lathe to the bench?

Mass usually doesn't hurt....especially with a light lathe.

Dave

 

[speedyb]

yes definatly will bolt to the bench!

I did find one possible source of the problem....and am I glad I did...

I was loosening the nuts on the chuck studs...one seemed loose already..

and then when I put it back on....SNAP. the stud snapped under the nut.

seems these studs are socket/allen wrench type, and the depth of the socket, along with the length of the stud....the nuts are all tightening down in a very weak area.
ie the nut does not go much furthere down than the socket area depth.

so I need to get some quality studs -but not a reccessed socket type evidently!

..edit...I should have noticed this anyway...the 4" chuck did not come with studs, so I used the ones from the 3". they are 25mm long, and I see that LMS sells 30mm long studs...

 

[steamer]

YES! Start there and see. YIKES a chuck coming loose like that would NOT be good!

Dave