Tailstock Alignment Question

DD,

So, if I understand your situation correctly, you've adjusted your lathe first by using the unsupported test bar and achieved .0002 in 5". Then you checked your tailstock alignment with your new test bar supported between centers and achieved .0005 in the length of the test bar. But, when you put a part in the chuck and support it with the tailstock center it pulls it out of alignment by .002 in 3". Is this correct ?

Ted

That's correct.
I also rechecked my spindle. Virtually zero but something less than .0004". I also checked my center which had .001" run-out.

How accurate is the centerdrill cut in the end of the piece you're turning. If it's not dead nuts concentric it will taper your part even if the lathe is perfectly aligned, tailstock and all.

DD,

Well, there's only a couple of things I can think of that would cause this. I don't know anything about your lathe, so I don't know if you have wear in the bed ways, or wear in the tailstock quill, but if there is wear, that could drop the center line of the center in the tailstock which could move your part off center when you drive the center into your part. Typically, the most bed wear will occur closest to the head stock. In your first post you said "I then tried turning a peice between centers, there is a taper there also", but when you later put your new test bar between centers you got almost no taper. That could be, as Epanzella said, that the center drilling in your part is not truly centered. The best way to accomplish a true center in the part is to chuck it as short as possible, center drill it and then clean up the taper using a lathe tool with the compound slide set for a 60 deg. included angle. This will in essence "bore" your taper on center. What type of chuck are you using when getting the .002 in 3" error ?

Ted

ddickey said:

I also checked my center which had .001" run-out.

Click to expand...

Ok, how do you have your center mounted and checked if you have .001 run out on it to start with. To that that could compound the problem

Epanzella & Talvare,
That makes sense about the center not being perfectly centered. I will definitely try your method next time I center drill a part.
No idea the brand of chuck. Lots of run-out on it, at least .015" if not more. My lathe is an old lathe made by Acra-Turn. For an Asian lathe it seems very well made but I've never had anything else to compare it to.
KV, I was talking the rotating dead center. It is a Bison mounted in my HS MT5-MT3 sleeve. I had my Noga mounted on the carriage with a DTI on the center.

I was thinking that I had heard that sometimes that sleeves can cause it to be out a bit which also compounded by an off center drill point you have your variation.