I want to center drill a large shaft. The shaft is about 24" long and
is from an old machine tool, but the ends were never drilled for centers.
The shaft is too big to pass through my lathe spindle. I can suss out how
to face the shaft off square, lay out and centerpunch a hole as closely
as I can, and I can then chuck one end of the shaft on the last 1/8" of
the jaws and hold the other end in my hand and gently "pick up" the
centerpunch with a center drill in the tailstock chuck. That way would
get me pretty close, but it would not be exact. I could then mount it
on a center in the tailstock and bring up a steady rest and then remove
the tailstock center and using a tiny boring tool, bore the center, but
how do I know the steady rest isn't just a little bit off?

What is the *actual* procedure for this?

Grant

Hey Grant,

A (fixed) steady rest is the proper thing, if you have one. Just
chuck one end in the three jaw, and in the steady rest as close to
"even" as possible by eye at the other end. (You could fiddle around
with dial indicators, setting it dead on, but it's not necessary).
Run very slowly, and you will be able to pick up the centre with no
trouble with a sharp small lathe tool in the compound. Use that
located point to centre drill into. Repeat for the other end.

Take care.

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXXXXXXX
On Sat, 05 Mar 2005 09:23:10 -0800, Grant Erwin
wrote:

I want to center drill a large shaft. The shaft is about 24" long and
is from an old machine tool, but the ends were never drilled for centers.
The shaft is too big to pass through my lathe spindle. I can suss out how
to face the shaft off square, lay out and centerpunch a hole as closely
as I can, and I can then chuck one end of the shaft on the last 1/8" of
the jaws and hold the other end in my hand and gently "pick up" the
centerpunch with a center drill in the tailstock chuck. That way would
get me pretty close, but it would not be exact. I could then mount it
on a center in the tailstock and bring up a steady rest and then remove
the tailstock center and using a tiny boring tool, bore the center, but
how do I know the steady rest isn't just a little bit off?

What is the *actual* procedure for this?

Grant

little late but....

Ummmmm....provided it is round and true of course. Guess a shaft
doesn't have to be, but I assumed....

Brian

Grant,
I have had to do this many times before I had a large lathe. First, I assume
you have enough space between centers. Chuck a piece of scrap in your chuck
and turn it to the same diameter of your shaft. Then set up your steady rest
around that piece of scrap so you have the correct pressure on all 3 legs.
Lock the adjustments and move the steady rest to the tail stock end of the
bed. Make certain the carraige is moved first. Chuck your shaft on the left
and suspend the shaft on the right. In the case where your OD is rough, turn
a small area clean close to the chuck. Then turn the shaft around and use
the steady in the machined area. You can go back and forth a couple of times
and then reset the scrap diameter and then the steady, sneaking up on the
problem. Keeping the carraige close to the chuck and using just the
tailstock, center drill the end. If the end of the shaft is not square and
requires facing, simply position the carraige to the right of the steady and
do that first.
Steve


"Grant Erwin" wrote in message
...
I want to center drill a large shaft. The shaft is about 24" long and
is from an old machine tool, but the ends were never drilled for centers.
The shaft is too big to pass through my lathe spindle. I can suss out how
to face the shaft off square, lay out and centerpunch a hole as closely
as I can, and I can then chuck one end of the shaft on the last 1/8" of
the jaws and hold the other end in my hand and gently "pick up" the
centerpunch with a center drill in the tailstock chuck. That way would
get me pretty close, but it would not be exact. I could then mount it
on a center in the tailstock and bring up a steady rest and then remove
the tailstock center and using a tiny boring tool, bore the center, but
how do I know the steady rest isn't just a little bit off?

What is the *actual* procedure for this?

Grant

"Grant Erwin" wrote in message
...
I want to center drill a large shaft. The shaft is about 24" long and
is from an old machine tool, but the ends were never drilled for centers.
The shaft is too big to pass through my lathe spindle.

Machine a female cap to slide snuggly over the end of the shaft. Drill a
hole in the cap the size of your centerdrill and use the cap as a drill
bushing.

It seems to me a drill mounted in the tailstock chuck would "seek" true
center the same as if you were drilling into a spindle mounted chuck. OTOH
a boring operation would tend to preserve any off-center effects done on
either end.

Bob Swinney
"Grant Erwin" wrote in message
...
I want to center drill a large shaft. The shaft is about 24" long and
is from an old machine tool, but the ends were never drilled for centers.
The shaft is too big to pass through my lathe spindle. I can suss out how
to face the shaft off square, lay out and centerpunch a hole as closely
as I can, and I can then chuck one end of the shaft on the last 1/8" of
the jaws and hold the other end in my hand and gently "pick up" the
centerpunch with a center drill in the tailstock chuck. That way would
get me pretty close, but it would not be exact. I could then mount it
on a center in the tailstock and bring up a steady rest and then remove
the tailstock center and using a tiny boring tool, bore the center, but
how do I know the steady rest isn't just a little bit off?

What is the *actual* procedure for this?

Grant

"Grant Erwin" wrote in message
...
snip
I could then mount it
on a center in the tailstock and bring up a steady rest and then remove
the tailstock center and using a tiny boring tool, bore the center, but
how do I know the steady rest isn't just a little bit off?

What is the *actual* procedure for this?

Grant

Mount in a steady rest, c'drill and bore centering taper for live center.
Then you have a true center to re-set your steady rest (if you need it). It
doesn't matter if your steady rest is not "dead nuts" when you bore your
centering taper, as long as it is close. It will only change the angle
slightly. It will still be on center by the nature of the beast (you have
the O.D. trapped).

On Sat, 05 Mar 2005 09:23:10 -0800, Grant Erwin
wrote:

I want to center drill a large shaft. The shaft is about 24" long and
is from an old machine tool, but the ends were never drilled for centers.
The shaft is too big to pass through my lathe spindle. I can suss out how
to face the shaft off square, lay out and centerpunch a hole as closely
as I can, and I can then chuck one end of the shaft on the last 1/8" of
the jaws and hold the other end in my hand and gently "pick up" the
centerpunch with a center drill in the tailstock chuck. That way would
get me pretty close, but it would not be exact. I could then mount it
on a center in the tailstock and bring up a steady rest and then remove
the tailstock center and using a tiny boring tool, bore the center, but
how do I know the steady rest isn't just a little bit off?

What is the *actual* procedure for this?

Grant
Lotsa good suggestions here. But if you haven't done it yet and have a
stout live center this is the method I use. The shaft needs to be
round and the face fairly square. A good saw cut is adequate. Put the
steady on the ways and clamp it. Put the shaft in the chuck and
tighten some. Adjust the steady by eye so that the shaft is fairly
well centered. Grab a piece of scrap aluminum and put it against the
face of the shaft, while holding it there bring the point of the live
center against the aluminum. Tighten a little and then back off the
steady a bit and use an indicator on the shaft OD to measure runout.
Use a hammer to tap the shaft into true. You may, and probably will,
have to tighten the center against the shaft while doing this. Once
the shaft is running true bring the steady contacts to bear against
the shaft OD. Back off the live center, tighten the chuck well, and
drill it. If you need the center to run truer than .001 bore it after
center drilling. This method takes longer to read than to do.
Eric