center-drilling large shaft?

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
Reply to
Grant Erwin
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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
Reply to
Brian Lawson
little late but....
Ummmmm....provided it is round and true of course. Guess a shaft doesn't have to be, but I assumed....
Brian
Reply to
Brian Lawson
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
Reply to
Steve Lusardi
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.
Reply to
John Kunkel
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
Reply to
Robert Swinney
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).
Reply to
Mtlgd
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
Reply to
Eric R Snow

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