Proper Use of Center Drill

Let me get this straight:

-Center drill rod at one end, place against live center in tailstock.
-Hold opposite end in the Three Jaw Chuck.
-turn entire length of rod down to certain diameter (it would help us help you to share these numbers :).
-Measure runout - at what part of the work piece?.

If you are NOT turning the whole length of the rod down, there could be runout at the three jaw chuck end for sure.

If you are working with a piece that is already the correct diameter at one end (so you aren't turning that end down), that end needs to either be on a live or dead center, or indicated in place in a four jaw independent chuck.

Lastly, you might want to get a quick look at your live center - I doubt this, but if your center is not working properly or damaged, to the point of .015, you can see it if you pull on the tip sideways or turn it.
Also- live centers require you to have the tailstock exerting pressure toward the headstock end for a live center to stay aligned.


Bernie
 
Since you are using a three jaw chuck for this, it is possible that the problem is the chuck. The jaws may be out of alignment or just worn or the chuck may not be seated properly on the register.

Do you have a four jaw chuck? If you need a tight tolerance it is best to use the four jaw or a good known collet if you're running those.

Steve
 
Here's what I do. I chuck the work as close to the chuck as possible, make sure the outboard portion of the work doesn't 'wobble' in the spindle hole. I use a homemade 'spider' to support the outboard section of long work. I then face the work, center drill and chamfer. I move the work out to the live center and turn the OD from there. Depending on how critical the dims are, I will sometimes center both ends and use a 'dog' to drive the work. If the piece is long and flimsy, you will need some type of follow rest to reduce the flex in the middle of the work.

Remember; center drilling in the chuck only assures the divot is in the center of the lathe axis, not the center of the work. Chuck, tailstock and tool run-out will all contribute to out of spec results. Check the chuck and tailstock for alignment periodically to insure everything is lined up properly.
 
I may have missed something. Has this been turned already to a dimention and want to center drill it and its off (runout) ?
If not been turned, shouldnt be any problem. Center drill what you have, dead center it and turn away providing the tail stock
is dead on as said first to check, or youll be taper turning. Example; your stock is say .500 you need ..450 so you take .050 off
it will be straight as an arrow > just do not unchuck it until you get the results. Center drill; good habit is very light pecks until
it starts to cut. So dont be concerned with run out, its going to be turned. Bigger stock always better. Ex 2 If you have a
piece in hand and 'oh no' would be good another .0015 or something turned ,, forget it. start over.
 
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