Turning between centers

[bigchicken]

Hi, I am new here and not sure if this is in the right section or not but here it is.

I have a couple of 6 inch long shafts that I need a taper on both ends, so I thought this would be perfect for turning between centers. My plan was to taper one end, flip the shaft and taper the other end. My problem is when I remove the shaft (not even flip it just take it out and put it back) I lose my concentricity, if I don't put the shaft back exactly where it was, I get runout anywhere from a .001 to perfect if I get it back "clocked" where it was.

I am going for the least runout I can get but is this as good as it gets between centers?
I was under the impression between centers had great repeatability and basically no runout?
Anyone experienced this before?

Thanks for any help.

 

[ChazzC]

How are you centering the two ends? And have you used/made a test bar to insure the tail stock & head stock are aligned?

 

[bigchicken]

Both ends where drilled with center drills from shars, I am starting to think maybe the drills are not actually 60 degrees.

Yes, the lathe is perfectly aligned .0001" difference on diameter in 6 inches of length.

 

[mmcmdl]

Dead or live centers ?

 

[tq60]

Are the holes burr free and deep enough to keep point from bottoming out?

Did you true up the shaft first?

The center is fixed so should be no runout after removing.

Try this.

Place work between centers.

Place dial indicator to measure the runout at the end of shaft, start with tail stock then check headstock.

If using a live center in tailstock, hold the part and rotate the center, the DI should not move.

Next, hold the center and rotate the part, still should not move.

If moves, the part that is being rotated has the problem.

Sent from my SM-G781V using Tapatalk

 

[ddickey]

Did you check the runout of your rotating dead center?

 

[RaisedByWolves]

Did you check the runout of your rotating dead center?

My first thought.

Also, have you given thought to how you’re going to hold the tapered end when you turn it around towards the headstock?

 

[bigchicken]

Try this.

Place work between centers.

Place dial indicator to measure the runout at the end of shaft, start with tail stock then check headstock.

If using a live center in tailstock, hold the part and rotate the center, the DI should not move.

Next, hold the center and rotate the part, still should not move.

If moves, the part that is being rotated has the problem.

Doing this solved it. The live center in the tailstock was causing it. When I rotated the live center, I started getting runout until I made a compete turn. I switched to a dead center in the tailstock and all is good, I'm so glad I started with a test piece.

My first thought.

Also, have you given thought to how you’re going to hold the tapered end when you turn it around towards the headstock?

My plan is to use a lathe dog with copper on top and bottom of the shaft.

Thanks to all for helping me.