Almost there, one thousanth of an inch

[ome]

Hi guys ,
spent a fewe good hours and still makes that jump on the indicator all of a sudde

any ideas would be very helpful
thanks,
Jon

 

[Tony Wells]

Jon, we need a little more to go on. What are you indicating, and on what machine, what indicator, etc. Every moving part of our machines should be smooth, and only if there is a flaw in the surface you are indicating should there be any sudden change on your indicator, generally speaking.

Have any pictures?

 

[ome]

jon, we need a little more to go on. What are you indicating, and on what machine, what indicator, etc. Every moving part of our machines should be smooth, and only if there is a flaw in the surface you are indicating should there be any sudden change on your indicator, generally speaking.

Have any pictures?

t i had my machinist friend make me up1" diameter test bar with a good center drilled at each end
i indicated off the test bar about 1.5" away from the jaws.
Thanks.
Jon

 

[Ray C]

ome,

Which chuck is that, the Cushman? Nice looking.

Indeed, as Tony said, a small imperfection will show up in the DI reading. It could be an issue in the bearings or even a chipped tooth in the gears. Try disengaging all the gears. Could even be a problem in the live center bearings. -Which brings-up another issue. I presume you're adjusting your chuck and if that's the case, using a live center is complicating issues. Let us know what you're up to there -what's the end goal? and we'll try to give a push in the right direction.


Ray

 

[stupoty]

Is it the same if you reverse the test bar (end to end) ?

Does it do the same if you mount the test bar between centers?

Stuart

 

[itsme_Bernie]

Yes, I didn't think it helped much at all to put a nice test bar on anything but dead centers on each side. I think putting a test bar on a chuck and live center tests the chuck and live center more than the alignment if the lathe?



Bernie

 

[Bill C.]

Hi guys ,
spent a fewe good hours and still makes that jump on the indicator all of a sudde

any ideas would be very helpful
thanks,
Jon

Double check your alignment of your indicator point. Make sure it is dead center of the test shaft. It can give you a misreading when you turn the chuck in one direction then reverse direction,

 

[Tom Griffin]

Jon,

A "jump" in an indicator is caused by a local imperfection on what it's running on, any misalignment would result in a more gradual change. Your set-up is also incorrect for anything you are trying to do. If you want to check the alignment of the spindle centerline with the bed (twist), you need to chuck the bar and leave the right end free. If you want to check for headstock and tailstock alignment (taper), or the runout on either center you would hold the bar between centers. You are attempting to use both set-ups at once and they are fighting each other.

I suspect you are trying to align the spindle to the bed, so I would suggest using Rollie's Dad's Method covered here.

Tom

 

[tarmo120]

test bar with a good center drilled at each end.
Jon

When I was starting lathe work, I watched the tubalcain videos. And in one video he specifically tells why to center drill and then re-cut the 60 degree surface. Because the center drill will not give you as accurate surface, you want at this time.
He drilled it in 4 jaw chuck, then indicated the freshly drilled center and it was off about .008''. Then in the same operation(didn't remove the stock) he re-cut the 60 degree angle.
4 jaw because he indicated the stock very accurately to absolute center.
I would check the centers.

 

[ome]

Hi guys,
sorry for the pic, i do not have a center touching the teat bar , only one end in chuck. It is a new buck chuck adjust tru 6".

I am trying to use the adjustment screw to get it on dead center zero.
I put the test bar in more so only 2 " sticking out, and that made a difference, it was 11 thou out, now it is 1 thou out.
Thanks
jon