lathe centers alignment

Humble request for advise (or sympathy): Just unboxed my new Jet 1014 and while checking it over, noted that the alignment of the tips of the headstock and tailstock centers is not perfect. The tailstock center is perhaps .010 or .012 inch lower than the headstock center. This is when the tailstock is moved right up close to the spindle. I've read somewhere, probably on this newsgroup, that when a tailstock center is tightened onto or into a piece of wood, that the tailstock center has some tendency to raise up. Depending of course on the bed's rigidity and the tailstock stiffness as well. My question, then, from anyone who might have encountered about this type and amount of misalignment in a wood lathe, should I worry? Jiggling things around does not seem to alter this alignment at all, and correcting this error would probably involve milling a few thousandths off the headstock base. Something I'm not very good at with my file and emery cloth!

Old Chief Lynn

Reply to
Lynn
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Not to be too flippant about it, but just forget it. That isn't bad for the Chiawanese these days. And honestly, you won't notice.

In a perfect world with perfect machinery, maybe. In all practical use, I don't think it will be an issue because 1 / 100th of an inch could just as well be in your Chiawanese revolving spur, your drive spur, or it could be the way you have the tailstock set in the ways.

Also, think about that tiny amount spread out over the length of what you are shaping. Doesn't amount to much.

And if it did bother you, what would you do to fix it? Just because the drive spur point and the revolving spur point don't touch, what would you adjust?

Then... it gets better. If you are thinking that you will always be holding your piece in perfect coeccentricity while turning, thing again. What happens when your revolving spur wears? And of course, what happens when your drive spur wears and you need to sharpen the blades a couple of times? Will you be maintaining machinist's tolerances?

Nope.

As an easy field exercise to prove this, think of when you dismount a piece of wood that you will be remounting on the spurs between centers. You ALWAYS mark an index point so you can remount the same way it came off, right? Think about it, if these things worked to machinist's tolerances it wouldn't matter how the wood went on or came off, no matter how many times as it would always line up the same.

I say spin up some wood and let the chips fly. Enjoy your new machine.

Robert

Reply to
nailshooter41

Hi Chief, I agree with Robert that our lathes, hand held cutting tools, the material being cut and the form of the turned objects don't have and don't need the accuracy and precision of turning on a metal lathe.

There are limits, of course as what we should reasonably expect of any new machine. Why not ask technical advice of the dealer or the maker if their quality control allows the tolerance this particular machine has?

If there is a mismatch at the headstock does this suggest a warped unseasoned bed, poorly machined ways and/or stocks, or even flash or grit between the bed and headstock? Loosen the headstock and check, clean it, but I certainly would not attempt to machine it.

Will you enjoy your new machine and be satisfied over the life of your lathe knowing it's imperfect to some degree? Does the mismatch vary along the bed length? Is the mismatch amplified enough on long spindles to matter? Is vertical displacement different from horizontal?

You might try different centers and see if the tail center makes a circle and if so how big, instead of a dot on the tail end of blanks of different lengths. I doubt that you could hold a tool on the rest with enough precision to check for taper along the ways as machinists do.

In the end I guess it boils down to your personal feelings about a slightly imperfect brand new expensive machine that you will be using for some time. There are probably worse imperfections in your shop. There sure are in mine. :)

Turn to Safety, Arch Fortiter

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Reply to
Arch

I would try turning on it, and see if I could turn the way I wanted to using the machine. I have two Jet minis, and never checked them since they do fine. Besides, it has been so long since they have seen new drive spurs or centers I would have to buy one of those machined gizmos to check it.

I'm right there with you, Arch. In my case, your humble scribe is the worst defect in the lot!

Robert

Reply to
nailshooter41

As the others have said, that's not enough variance to matter, unless it was a metal lathe and you were making aerospace stuff.. Also, the alignment can appear different from different viewing heights and angles.. It can make you crazy..lol I put a piece of cardboard between centers and gently advance the tailstock ram.. Then, you can "read" the holes.. If I can see only one place that the light shines through, I'm happy..

Remember when checking.. Both centers must be firmly seated in clean Morse tapers and the headstock and tailstock locked down..

mac

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Reply to
mac davis

Reply to
c.les hewitt

lynn - believe it or not, cast iron flexes - it is possible that the way the lathe is bolted to the stand is flexing the ways - this is certainly an issue with larger lathes (such as my 1200 pound metal lathe), so it could certainly affect yours

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Reply to
William Noble

Good point, Bill.. There is also a bit of flex on all of my lathes when the tail stock spindle is extended.. I sort of expect that and try to get as close as I can to the work before extending the tail stock to apply pressure to the piece..

mac

Please remove splinters before emailing

Reply to
mac davis

Thanks to all for the wealth of experienced advice. There are few groups that share so readily.

After reading those responses, and doing some actual thinking (!), I'll probably just ignore my alignment imperfection. However, putting some thoughts together, I think that what actually caused the head and tail stock centers misalignment is worth considering.

How true, that iron is not perfectly rigid.

But if misalignment is apparent, and the axis of both the spindle and tailstock are exactly parallel, that would be one case. (a difference in the height from the bed) But suppose the misalignment was due to either the spindle or tailstock not being perfectly parallel to the bed. Were the headstock (spindle) not exactly parallel to the bed, then it seems like the further the tail is from the head, the worse the problem could be. Does that make sense?

I suppose that my Jet with a 14" bed, that won't be enough to worry about.

Thanks again, Old Chief Lynn

Reply to
Lynn

But then you put this really large *BUT* in there...

Absolutely NOT. Totally unfounded. This is a false trigonometric argument. PERIOD.

This is not a compounding, cumulative error. This error could only be of a multiplicative nature IF one end of the extrapolated triangle was WAS set, and the other was NOT set.

You have nattered this math problem down to the point you are chewing on the bones.

Let me try it this way:

Imagine yourself standing in front of your lathe with the headstock on the left hand side. We are not looking at bowls, winged shapes, warped and punky wood, offset turnings, etc. For purposes of illustration, think of a round piece of hard maple spindle stock.

Say your headstock/tailstock (now known as hs/ts) is out of alignment of a perfect center by 1/100 in one inch. That would mean that if one side was perfectly stationary, then in two inches it would be

2/100 (I know, 1/50th). At 3 inches, 3/100ths, and so on and so on. Then you get to 14 inches, which is the max working length between centers on your lathe.

WITHOUT the end ts being secured (remember, working left to right) you would have a cumulative effect of being 14/100ths ( a little more than

1/16th of an inch ) off center.

BUT BUT BUT.... your ts holds the piece in place, at near perfect coeccentricity at the ts. In your case, the difference at the hs/ts detail is about 1/100. This means that at the other side of the two revolving axises of the lathe, it is still only 1/100.

Don't believe me on how little this matters?

Think about it this way. When you turn a spindle, you are moving your piece into a concentric shape with every pass. So try this:

Make a temp gauge that is 1" in diameter (a one inch wrench will do fine), or use a good set of calipers. Take a piece of wood about a foot long or so, and secure it between centers. This long piece will help you understand why the effect doesn't multiply.

Round this piece of wood carefully, until you get it a perfect one inch diameter from hs to ts.

Wasn't that hard, right?

Where did the difference or cumulative error go? It went nowhere because there isn't any!

(In case anyone is actually reading this... the error would show up on the ends as the surfaces perpendicular to the error.)

The important thing to remember is that YOU will establish a round, coeccentric shape every time you turn. By the nature of the lathe, you are spinning the wood on an axis determined by you. You establish a new line of coeccentricity. The lathe spins the wood on that axis, and that is all there is. With both sides of your line secured, there is simply no way for the error to accumulate or compound.

Besides, since you are looking at this with your machinist's micrometers and calipers, how do you secure your wood to the lathe? Do you use a spur and tailstock revolving center? When you attach or suspend your piece to the lathe, is your technique such that you can gauge both sides (hs/ts) to less than 1/64 of an inch difference in penetration to hold that piece perfectly.

I doubt it.

And once again, it doesn't matter if you did. The sides are the bearing/holding points for a piece of spindle work. When you turn it round, you have brought it into round, the level of perfection being your limitations as a turner.

But while you are nattering this problem into tiny pieces, think about this: NONE of this matters (even for a hypothetical argument) if you get a piece of wood that had dried unevenly, has hard spots or voids, is kind of green, it is reacts quickly to exposure to air, has a few knots, is left on the lathe overnight, has hidden bug tunnels in it, and on an on. All of those things will throw your piece out of round by affecting the density of the wood in different areas of the piece. THAT is what you watch for.

You are over thinking this. Go outside, put some wood in the lathe and turn a spindle every way you can to see if you can get it to screw up. It won't happen.

Enjoy your lathe. These are nice machines. I have two, and do almost all my turning on them and have for years. Don't ruin this for yourself by dwelling on pointless details that in the end don't matter.

Robert

Reply to
nailshooter41

Great, Robert! I intend to take your advise, "Don't ruin this for

I do follow your explanations well, and I guess if the spur drive is being used, there would be sufficient flexibility to take care of any very small misalignment.

BUT (again), help me, if you are still reading, to understand what is occurring if a longish piece of stock is clamped solidly in the chuck (hs), and turning slowly. (ts end not yet secured) Now the stock is turning on an axis established by the spindle. Due to the slight misalignment problem, that stock's ts end axis does not point at the ts's center! If the ts's center is now cranked into the stock, it appears that something has to give. I imagine the ts's center would wallow in an enlarged center hole, or the stock would have to flex.

Old Chief Lynn (whose trig is but a stack of dusty, unused books)

Reply to
Lynn

Lynn wrote: Were the headstock (spindle) not exactly : parallel to the : bed, then it seems like the further the tail is from the head, the worse the : problem : could be. Does that make sense?

I think it's the other way around. The further apart the two centers are, the less the difference between (a) the line from one center parallel to the bed, and (b) the line between the tips of the two centers.

And I don't think the lack of parallel you mention in your original note matters.

-- Andy Barss

Reply to
Andrew Barss

The issue here is the students have not gotten all the data, and the data given is not fully defined.

Lets take a new out of the box lathe.

Lets let the bed season and settle while coming to temperature.

Then we level the lathe. Across and end to end. Jacking the feet as needed to become true. [ in this process you might loosen the leg bolts to allow movement. ]

Settle again and re-true. Beds gets stressed all the time if not proper.

Then and only then can we start looking at a center to center head to tail.

If not level in both x & y directions or if you didn't get it done completely: If there is a bed warp or twist the tail center will float all around if measured from a constant head stock or a line or standard off the lathe.

If a lathe is level - wood lathes normally need less, but if one does precision work - work with precision tools and instruments.

If level then check center to center.

If the tail stock is offset 1" to one side or the other then tapers (massive ones) can be cut. Normally the offset is much less as it in effect doubles.

So in-line is important - when working with projects like pool queues or drum sticks or other thin spindle or bowl edge. You want to put in the taper you want, not what the offset does.

Up and down offset means the lathe wasn't manufactured correctly.

With luck the tail stock is split and allows sheet shim stock (brass or Steel) to be placed in order to lift up one or the other end. Or the headstock...

The lateral offset is by two setscrews on the tailstock.

I own bot Metal and Wood lathes and use both.

Martin

Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member.

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Reply to
Martin H. Eastburn

Lynn got it also.

On tapers - you can find tail stock centers on a bar. A morse taper on one side, A heavy bar on the other end with fixed center points at various offsets. Prevents jacking with the tail stock. Martin Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member.

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Reply to
Martin H. Eastburn

OK, this is getting silly.

Worse, you have now completely changed the entire parameters of why you were checking the tailstock. Are you going to use a CHUCK now, which was not mentioned until this post?

If you are worried about your hs/ts lining up, that is one issue. I am guess you didn't try the experiment I suggested, but just sat down with another question and banged it off.

Now you slide in another problem/question altogether with your mounting procedure into a chuck. REREAD my earlier post. I explained that since BOTH SIDES ARE SECURED IN A SPINDLE >>(not specified, but you know they centered with a pin)

Reply to
nailshooter41

I don't have enough sense not to add to such an exciting thread. :) So for my two net friends: For Robert, I take your point and retract my previous confusing post mixing offset turning on an axis parallel to the bed with an angled axis. For the old Chief, re your humble request for optional sympathy, you have mine. :)

Anyway, you're gonna love that little lathe. but you probably shouldn't begin by making eccentric turnings. (there I go again) :(

Turn to Safety, Arch Fortiter

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Reply to
Arch

Thanks, Robert, You have been more than generous in explaining the difference between impractical thinking (mine) and doing. I've gradually progressed (over the past 70 years) from dad's Sears Dunlap lathe, with tools I ground from old files, to my homemade, then a Grizzly (best of all, so far), and now this little Jet. .........Caution, Robert, another "rabbit trail": .......... My concern with alignment probably grew from tinkering with my shop's little "pre-war" Dunlap metal turning lathe. In the late 1940's I "horsetraded" it from a fussy machinist who spent many hours trying to make it perfect......... but failed. I never mastered it, but learned to appreciate those who could perform miracles with greasy machinery. Cheers, Robert, and thanks for taking the time to send me back to the shop.

Old Chief Lynn

Reply to
Lynn

Anytime. The last post may have sounded a bit cranky, but not intended that way.

It is difficult to try to explain something in writing that would take a few minutes in person. I am glad I could help.

Now.... remember this... when the next guy comes along and you can help, you're up!

;^)

Robert

Reply to
nailshooter41

You do make me laugh, good sir. When I read your post I was laughing out loud.

Still snickering, too...

Robert

Reply to
nailshooter41

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