PM 1440 - First Failure

Ever hear of "Machinist's Elbow", caused by forgetting to remove the center?

Since you may want to machine to finer precision than you can see, the better way to center the tailstock is with a chucked indicator riding on the conical surface. A quick check is to grab a milling edge finder in both the spindle and tailstock chucks.

--jsw

I figured I'd use an indicator to dial it in closer when I need it. Not sure I agree about the edge finder. I am sure my tail stock drill chuck isn't "that" good, and I tend to leave the three jaw on the head stock for speed. I keep trying to convince myself I can learn to be as fast as the guys showing off on YouTube with their 4 jaw, but I don't think I have another two ot three decades to master that skill. LOL.

I don't know whether this is common knowledge or not, but an old machinist showed me how to get the alignment pretty damned close without a loupe. You bring the two points together, and capture a piece of flat stock between t hem - he used his 60 degree center gauge. Any misalignment becomes immediat ely obvious by the tilt of the metal.

• I don't know whether this is common knowledge or not, but an old machinist

• showed me how to get the alignment pretty damned close without a loupe.

• You bring the two points together, and capture a piece of flat stock between

• them - he used his 60 degree center gauge. Any misalignment becomes

• immediately obvious by the tilt of the metal.

That makes perfect sense. I use a metal scale all the time to set the height of tool holders. Don't know why I didn't think of doing that between centers. Nice.

A trick for that is to zero the indicator dial with the crossfeed on a low jaw, rotate halfway to the high jaw, then adjust out half the reading. Two revolutions get me within a few thousandths, then I position the indicator for equal + and - deflections around a major division.

--jsw

Bob, I don't know how much trouble you want to go to on this job, but you might consider reaming for a taper pin.

Tom

If you are worried that the tail stock center doesn't come to a sharp point just grind it.

Back in the days of turning between centers it was a common job for apprentices. Make sure that both the headstock and center were clean and had no burrs, install the tail stock center in the head stock and re-grind it with the tool post grinder. Usually both centers were ground at the same time.

Why would one want it to be sharp? Other than for aligning the tail stock?

Well ... there are hardened centers, designed to go in the tailstock, and mild centers, designed to go in the headstock and be trued up before use. The hardened centers are more likely to have good sharp tips.

But remember -- the center drills are designed to drill a small hole followed by a 60 degree countersink so the point normally floats in air -- or in whatever lubricant you may have put in the center hole. :-)

As an alternative way to center the tailstock -- do you have a Blake Coax or one of the import clones thereof? If so, put the shank of the coax in a collet or in the chuck (collet is better, if you have them), and set the finger to either trace the ID of the Morse taper socket in the tailstock ram -- or put the center in and trace on the OD of it. Set the spindle to a slow speed (back gear) and adjust the tailstock to minimize the wiggle of the needle. Note that some lathes when new come with the tailstock just a little above center, so as the tailstock wears, it first gets closer to center before it starts getting worse, so you proably won't be able to find a truly wiggle free position.

Good Luck, DoN.

That's probably the best idea yet for the next time it fails. A tapered solid pin will be stronger, and it has the advantage of being able to be tapped out. As opposed to a solid dowel Loctited in place that would also require heat to knock out. It was already all back together with another under engineered spring pin when I posted, but as I said before I expect it to fail again.

Thank you.

I might do that, but I think I'll indicate it in next time I need real precision. I do have a cheap crap coaxial indicator and a couple decent Last Word indicators that haven't been dropped yet. I'm sure I can make one of the work ok.

I don't have a tool post grinder. I am working on a tool post cross drill though.

Um... ok. LOL. Thanks Bob.

I don't think eaither dead center I have is hardened. I may just have to go out and spend a 3 dollars on one. There are times when I really need a dead decenter rather than a live center for turning.

But... But... But... I might forget.

Crap clone. And a couple Last Words and an inspection mirror as an alternative.

I may try the pinched plate method just to see how it compares for results.

BTW -- at one time, a "live center" was simply the rotating center in the headstock spindle, and the dead was one in the tailstock. They were otherwise identical -- if the same Morse taper. Once we started getting centers mounted in bearings so they could rotate in the tailstock, the name drifted.

And the "live" one in the spindle was typically soft so it could be trued *just* before mounting the workpiece. The "dead" one in the tailstock was more likely to be hardened.

And have you ever seen a "half center"? A hardened center for the tailstock with almost half of the diameter ground off so a facing tool could get to the center hole to finish the end of a shaft. I've got one of those -- but too small for my main lathe. Nice for doing things that the ball bearing center won't allow.

In which case, let it remind you. :-)

Old lathes tended to have a cavity in the casting near the front where the ram comes out, and a plug/dipper in there. It used to be filled with white lead to use as a high-pressure lubricant for the dead center -- before the world got scared to death of lead and mercury. :-)

O.K. So you have those as an option.

I didn't mention the pinched plate because of the questionable state of your centers. I first learned about that in the manual for a Unimat SL-1000 (where the headstock rotated instead of the tailstock offset for turning long tapers). And they showed a double-edge razor blade as the pinched plate. I often use a 6" scale for quick-and-dirty center checking.

Enjoy, DoN.

It's good you brought that up. A lot of more recent home machinists may not realize this. A live center is one driven under power. A tailstock center with ball bearings is...a ball-bearing dead center. d8-)

For precise work, you mount the live center and turn a new point on it with the lathe compound. Then punch a witness mark on it, and a matching one on the center collet, so you can line them up again later for less-precise work.

Mine is still filled with white lead (1945 South Bend 10L). My tin of it is almost empty, though.

On Tuesday, November 29, 2016 at 10:12:54 PM UTC-5, snipped-for-privacy@gmail.com wrot e:

BTW, traditionally, dead centers are hardened only for the last 1/4 inch or so. All of mine are, and they're 60 years old or more. The hardening leave s a distinctively different color to the steel -- the result is a cone 1/4" long on the very end -- so it's easy to tell when one is a hardened center or not.

O.K. But does it also match the tailstock? I can't see using a half-center in the headstock. :-)

Enjoy, DoN.