Live center help!

[Ricc Havens]

I have this live center and it's causing a problem. https://woodworker.com/live-center-assembly-2mt-mssu-134-792.asp
(https://woodworker.com/live-center-assembly-2mt-mssu-134-792.asp)Photo below - it's lableled Powermatic but looks like a Oneway.

I am turning travel coffee mugs with the stainless insert for an upcoming art/crafts fair. After drilling and hollowing the interior to fit the stainless insert I use the live center for support the mug when turning the outside to final shape and thickness. When using the large cone for support it will start to unscrew from the center while the lathe is spinning. If I don't catch it in time it can unscrew enough to jam into the mug further causing it to crack the wall of the mug.

If it's right hand thread and the lathe is running in that same direction you would think the cone would just tighten more onto the live center but instead it starts to unscrew. I use the rod that came with it to tighten it as much as I can by hand start turning again. And, in a very short while it starts to unscrew again. This has gone on as long as I can remember owning over the last 3-4 years. But since I rarely used it I didn't think much of it. Now that I am trying to get a dosen mugs ready for this craft show it's really annoying me - especially if it causes the blank to crack.

I'm pretty sure it's not bad internal bearing in the live center as the bearings don't make any noise when spinning the live center.

any ideas on how to correct the problem (I'm on disability so buying a Robust live center isn't an option :-) )

Thanks
Ricc
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[Jed Hefley]

Silly question, but, is there a set screw on it to bind it to the shaft?

[Ricc Havens]

Unfortunately there is not.

[John K Jordan]

[set screw?] Unfortunately there is not.


That looks like a much bigger cone than comes with those live centers. Are the threads tight or a little loose?

It should tighten when the lathe is starting from a stop. But could it be unscrewing when the lathe is decelerating while stopping? That's the only reason I can think of.

If you have a drill press and taps it wouldn't be too difficult to add a set screw. You wouldn't need threads all the way from the rim but could drill all the way sized for tapping, drill a clearance hole for the set screw, then tap just the last little bit.

JKJ

[Mike Tilley]

I’ve had that same issue myself ended up ruining the large cone when it came loose.
not sure causes it either

[George Troy Hurlburt]

You might try some white plumber's tape on it. Like what you would use on a garden hose. Might take up some of the slack.

[Leo Van Der Loo]

I’m sure Oneway would not label their live center Powermatic, however that is probably the problem, it is not made by Oneway.

Too loose a fit and some vibration could loosen the large cone, I would do what George advices, a wrap of teflon tape or even two would have the cone fit tightly, if you stick the pin through the center and tighten the cone firmly it should stay on, I have a Oneway live center and have not had any problems with it, and have used it enough in the 20 or so years I have had it.

Looking at your picture I would say you do not have a Oneway live center.

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Maybe take contact with Powermatic and see what they are willing to do for you.

[Bill Blasic]

The chrome Powermatic live center was only a short run as Oneway objected as it looked too much like theirs, hence that is why they are black. Do you still have the point in the live center when you are using the cone? As John stated it might be from stopping the lathe as that seems like the only way it could loosen and if the point is bottoming out in the cone it would not be getting as tight as possible.

[Bruce Schoenleber]

Get some Loctite thread locker, the removable (blue) type. It will make the cone difficult to remove.

[Hal Taylor]

I would suggest inserting a small rod in the holes of the live center to lock it from spinning while seating the cone on the live center. I’ve had this happen to me, but after seating the cone well, it won’t spin off.

[Dick Strauss]

It is a good idea to loosen the chuck slightly, bring up the cone and make it tight to the mug, then re-tighten the chuck so that the chuck holds the piece on the same axis as the cone. This will help prevent the bad cone to mug interactions you describe if the cone does come loose!

I assume you have the tailstock tight to the bed, the cone fully engaged and tight to the mug, and the screw handle on the tailstock is tight before you start turning the outside.

Forgive me for asking what might be a rather dumb question not having turned mugs with inserts.

Shouldn't the livecenter/ cone being tight to the mug/insert being tight to the chuck/headstock prevent the cone from unscrewing? If so, what is moving or slipping? Is the mug insert moving deeper into the mug recess as you start to take away the wall thickness or wall strength which would shorten the mug/insert overall length? Or, is your tailstock slipping during the process?

The distance between the head and tailstock has to increase or one of the components in the middle has to shrink in length to allow a fully threaded cone to unthread itself, right?

[Ricc Havens]

John J - It is the optional cone you can buy that screws onto 3/4-10tpi threads of the live center. Unfortunately it's not unscrewing as the lathe is decelerating it's doing it as I am turning. I thought about adding a set screw but there is no good place for the set screw to lock against the live center without damaging the threads of the live center.

George H. _ I will give the plumbers tape a try. thanks for the suggestion.

Leo - It's not the Oneway. It's made by powermatic/jet and looks like a oneway. there doesn't seem to be any slop in the threads. I use the rod to tighten it in place and use as much force as I can but it still comes loose while turning. I just re-tighten and continue turning and repeat as it comes loose again. It's just annoying. I've tried calling powermatic but the techs I have been able to talk to seem to no clue about using their wood lathes. they just want to sell me a replacement.

Bill B. The center point is still in place. BUT - it's not bottoming out as it goes into the hollow opening of the mug blank so the point doesn't touch anything.

Bruce S. - I will consider the loctite idea but if it's difficult to remove I'm not sure I want to go that route as I switch back and forth between center cones/points frequently.

Hal T - I do use the rod that came with the live center to seat it as tight as it will go but no matter how tight I try it still comes loose.


If anyone else have any other ideas please keep them coming!

thanks
Ricc

[Ricc Havens]

Dick S. - No dumb questions. Yes everything is lined up and tight including tailstock to the bed, cone being fully engaged to the mug blank, and the screw handle on the tailstock are all tight before turning. Nothing seems to be slipping or moving. It's just that the cone comes loose and as it does it will jam so hard into the mug )becasue the tailstock is tight in place and not moving) that it will either crack the mug blank or when I loosen the tailstock clamp handle I have to pull hard as the cone has unscrewed enough without the tail stock moving that it's jammed hard into the mug opening.

Ricc

[Jed Hefley]

Is it possible the live center is not perfectly aligned with the headstock? I use a wooden cone on mine, and if its not centered, it vibrates like crazy. Have you tried turning the outside without the aid of the live center? I’ve done 5 so far without it, and haven’t had any issues, other than the high pitched noise when wall thickness gets thin. All of mine were either segmented or staved, if that matters. Would parasitic drag in the bearing stack be the culprit?

[Dick Strauss]

Try to put a really fine sharpie marker on the bed at the base of the tailstock handle end. If the tailstock is creeping away from the headstock, the line will disappear as you turn. It seems as though some folks had a tailstock movement issue with Jet lathes a while back but I could be completely off base!

[Kyle Iwamoto]

Since you seemed to try everything, are the threads on both parts clean of any debris? Mine get all full of trash when I use the cup center. If you got junk on the threads, it will never seat correctly.

[Paul Williams]

I'm having trouble understanding this. If it is truly a right hand thread it should tighten with the lathe running, and the only way it can loosen is for the live center to turn faster than the lathe. That only happens when the lathe is slowing down. There is a lot of discussion about things that would keep it from centering accurately, but that isn't what I understood to be the question. Why would it unscrew while the lathe is running?

[Kyle Iwamoto]

Why would it unscrew while the lathe is running?

I often wonder about it myself. It happens to me every once in a while........ Usually when I tighten the cone with the small rod, it doesn't happen.

[Ricc Havens]

Jeff, I did check that and they are aligned properly. Thanks for the idea though. I have tried turing without a cone but I have had some success and some failures.

Ricc


Is it possible the live center is not perfectly aligned with the headstock? I use a wooden cone on mine, and if its not centered, it vibrates like crazy. Have you tried turning the outside without the aid of the live center? I’ve done 5 so far without it, and haven’t had any issues, other than the high pitched noise when wall thickness gets thin. All of mine were either segmented or staved, if that matters. Would parasitic drag in the bearing stack be the culprit?

[Ricc Havens]

Kyle, I do use the rod that came with it to tighten but still have the problem.

Ricc


I often wonder about it myself. It happens to me every once in a while........ Usually when I tighten the cone with the small rod, it doesn't happen.

[Ricc Havens]

Since you seemed to try everything, are the threads on both parts clean of any debris? Mine get all full of trash when I use the cup center. If you got junk on the threads, it will never seat correctly.

I did check the threads when I tried teh plumbers tape as suggested in an earlier reply above. But, still had the issue today.

Ricc


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[Ricc Havens]

I'm having trouble understanding this. If it is truly a right hand thread it should tighten with the lathe running, and the only way it can loosen is for the live center to turn faster than the lathe. That only happens when the lathe is slowing down. There is a lot of discussion about things that would keep it from centering accurately, but that isn't what I understood to be the question. Why would it unscrew while the lathe is running?

Paul, i don't understand it either. It is right hand thread. But it happens when the lathe is running and I am turning the mug - not when the lathe is slowing down.

The only thing I can think of is when I have it snug in the mug opening and apply pressure to the turning wood with a tool (either a parting tool, spindle gouge, or roughing gouge) that they cause enough pressure on the wood which slightly slows the cone down slower than what the live center is spinning causing it to unscrew. If that's the case, then why have a cone accessory like that available? No matter how tight I make it on the live center it will end up coming loose jamming into the mug.

I have checked the live center and large cone adapters from Oneway and Robust online and none of them have a set screw designed into their cone. And trying to add a set screw after market isn't feasible since neither manufacturer makes a place on the live center for the set screw to lock against. In the large cone there is only enough threaded depth for the threads of the live center. So a set screw would damage the threads.

This afternoon I borrowed a Robust live center and large cone from a local turner friend. It is a similar design with out a set screw for the cone. Right hand thread and tighten with a rod through the live center. It did the same thing but not as bad or as often.

Thanks
Ricc

[John K Jordan]

I thought about adding a set screw but there is no good place for the set screw to lock against the live center without damaging the threads of the live center.


You can use a set screw and not damage the threads. Set screws with soft tips are available. For example, search for set screw with nylon tip.

Also, some mfgrs use a tough fiber disk/plug to drop into the hole under the set screw to keep from marring the threads or shaft. You could make one from a bit of nylon, delrin, etc. Teflon or HDPE might be too soft. Carve a piece from some high impact plastic that everything from kitchen handles to lawnmower parts are made from today. Or make a tiny plug from lignum vitae, I think it would be tough enough.

How it can unscrew while turning is a mystery to me too. I'd like to see that. If it doesn't loosen when the lathe is simply spinning smoothly but does loosen when turning, I'd imagine some flexing of the hollow cylinder could be causing a backwards force in exactly the wrong place, a tiny bit each time, perhaps possible since the cone is only contacting the rim of the mug in a tiny ring.

This would be an effect similar to what I see when fencing with T-posts - if I need to remove a post by hand I might push it back and forth to widen the hole some then rotate in around in a circle to widen the hole even more - guess what, if I rotate the post in a wide clockwise direction the post itself always rotates in a counter-clockwise direction.

Perhaps another way to hold...
Regardless, in general I don't use cones since they can easily and accidentally apply too much force outwards and split the work. I almost always make something from wood with a diameter such that it slides snugly or jams into the hole for steadying, whether the hole is 1/4" or 3" in diameter. This "plug" is often a short cylinder (1/2" or so) and always has a shoulder so the rim of the work can press directly into the shoulder with as much force as I want with no danger of splitting the piece. I sometimes turn a short plug to fit then simply hold the plug with the live center. Sometimes I'll turn or drill a tight hole that I force or twist over the threads of the live center, then use the live center as a drive center to turn the plug/jam concentric and to the needed size (put a piece of wire into the small hole on the live center to keep it from spinning).

I now have a 3/4"x10 bottom tap so I generally drill and tap a block of wood and thread this onto the live center. Again, I'll use the live center as a drive center to turn the jam piece so it is guaranteed to be perfectly concentric.

I've made a bunch of these for special purposes and I keep them all for reuse, turning to a new diameter as needed.

Another way I hold things with a open hole on one end is turn a "jam" piece between centers (again with a shoulder) and turn a short #2 morse taper on the end. I fit this into the short morse taper of a Nova live center. I have a bunch of pieces now with a short taper that I adapt as needed. (Since the center has a #2MT hole the lathe spindle MT can drive the block for turning to size.) The Nova center is the most flexible center I've seen, so useful I just had to get two.
https://www.amazon.com/NOVA-5015-Center-System-Stepped/dp/B0064JIZGC

JKJ

[Kyle Iwamoto]

Perhaps you can try using a tennis ball, handball, doggie toy ball or similar to stabilize the end. I used them in the past to stabilize and turn goblets. Use the cup center with the balls.

[robert baccus]

Do you want the number for Madam LeDouche in New Orleans maybe yeah.

[Bill Blasic]

Ricc I was talking about the point in the live center that is there before the cone is attached not the point of the cone itself.

[Dick Strauss]

Stop the lathe every once in a while and tighten the cone/tailstock to the mug using the tail ram. This should prevent the problem while you figure out the cause.

Try drawing sharpie lines at the base of the handwheel ends of the headstock and tailstock on the bed to eliminate those two sources of movement.

You may also want to try a steady rest to help prevent off-axis motion.

Your mug insert is either pushing deeper into the recess, the tailstock is moving, the base of your mug is pushing deeper into the chuck, or the headstock is moving. A distance has to change at some point in the system for the screw to unscrew if everything is tight to begin your turning session! Screws only unscrew due to vibration when there is very little to no load against them. Think about a how a second nut on the same bolt will prevent the first one from loosening.

[Dick Strauss]

Another thought I just had....

What size tenon is left on the headstock side? I'm not asking about the part mounted in the chuck. In one of your pics it looks like you had undercut where the bottom of the finished mug will be. The area that was undercut looked to be about 1/2" towards the tailstock side along the turning axis from the chuck jaws. What diameter of material is remaining there? If it is a small area, those fibers can get deformed and compressed off-axis during turning if lots of force is applied.

[John King]

All remedies above aside, there is something very wrong here. If the lathe direction of rotation is correct for spindle turning, there is no way that the cone unscrews while the lathe is running. Proper lathe rotation will tighten the cone, not loosen it. It's designed that way so that the cone remains firmly attached to the live center while spindle turning. - John

[Ted Reischl]

My guess is that he has a draggy bearing in the live center. As he puts the tool to the work he slows the work, a draggy bearing in the live center would cause it to ever so slightly try to loosen up.

I see the hole for a rod, where does one place a wrench or another rod to allow it to be tightened?

I use a livecenter that does not have the built in point, a really, REALLY cheap one. It has machined flats so a wrench (that came with it) can be used to tighten items threaded on. Heck, I have mounted a chuck on and it never loosened up.

Guess it pays to be cheap?

[John King]

My guess is that he has a draggy bearing in the live center. As he puts the tool to the work he slows the work, a draggy bearing in the live center would cause it to ever so slightly try to loosen up.

Can't happen. As long as the lathe direction of rotation is correct for spindle turning, no way the cone loosens up because of a "draggy bearing." Even if the live center freezes/locks up solid, the lathe rotation will be such that the cone is tightened on the live center - not loosened. There must be something missing from the problem statement. - John

[Leo Van Der Loo]

Ricc I was talking about the point in the live center that is there before the cone is attached not the point of the cone itself.

It would appear that you do not have that live center, there is no point on the large cone, it is wide open on both ends and can be installed either way on the centers threaded nose.

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[Leo Van Der Loo]

Rick, what you are telling us, is something that actually is impossible to happen, taking the way things do fit together, however in a case like this, maybe you would be better off to build a tapered cone on your live center.

Take a good piece of hardwood and drill an opening the right size to tap tight fitting threads in it, fitting the centers threaded nose.

Stick a pin through the hole blocking the rotation of the center and install it in the headstock spindle, turn a taper on the wood that will fit you workpieces.

Install the center in your tailstock again and start turning, that wood should stay on and not loosen up IMO.

[Kyle Iwamoto]

Rick, what you are telling us, is something that actually is impossible to happen, taking the way things do fit together,

It happens. It's not impossible. I have the same center on mt Jet and it happens to me. This is extremely interesting to me too.

[Leo Van Der Loo]

It happens. It's not impossible. I have the same center on mt Jet and it happens to me. This is extremely interesting to me too.

No Kyle, only if the live center is turning faster than the workpiece it is supporting, would this be possible, and how would that happen ??, as I say, in the way these pieces are put together and the direction the pieces are threaded and the direction the lathe turns it is not possible, or could not happen.

The live center is not going to start turning faster just by itself, so in order to happen something else is going on, elasticity of the wood that after it was under tool pressure goes back and forth rotationally, and backs the cone off of the center ???, I don’t know, but a tighter fitting cone should make this less likely to happen I believe.

Not much to loose but some wood and time turning a new cone.

[Ted Reischl]

Mr. King, you are definitely right, my thinking was going backwards.

Here is a thought, and someone else sort of wrote about this. The only way it can come unthreaded is for the center to be turning faster than the workpiece. This might happen when the part gets thinner, pressure is relieved reducing friction between the center and the piece. Then when the tool is applying force the center has enough momentum to start creeping. I would not bet the farm on this idea.

All that said, I would not use a cone on a thin walled workpiece to start with. The cone is like a wedge trying to drive the piece apart. Instead, I would turn up a boss with a shoulder so the force is applied in line with the spindle when tightened. That is why I bought a live center with a threaded end, no cones. I have made up my own cones out of wood but rarely use them. Oh, and edit. . . I turned my cones with a 120 included angle so they apply more force in line with the spindle than outwards.

This is definitely a nasty problem. I am thinking that the aluminum cones are being applied to situations that they were not intended to be used for.

[Dan Hunkele]

From a mechanical view there is a possibility there is a crack in the threaded section. If a cracked nut is tightened onto a bolt the crack will spread and continue to turn on top of the threads until the threads are aligned again and then snap back into the thread grooves. At this very moment the nut will be loose again. Inspect the threaded section of the cone for cracks. Logistics say it can't possibly come loose in it's normal operational mode but stranger things have happened.

[Clint Bach]

It is possible with a real technical reason. There were telescopes with a hypercyclonic drive reduction. Incredible reductions in the order of 1000 to 1 or more. That reduction would put amazing pressure on the mug.

Just a very slight misalignment could cause this. As an example of the basic principle... spin a coin on a surface and watch as it slows down. The coin will rotate slower and slower the flatter the coin is to the surface.

The reduction ratio can be calculated by comparing the circumference of the coin's edge to the the circumference of the circle the edge of the coin takes on the surface. Very high reductions for the last few rotations of the coin.

How's that for a strange explanation... So... The cone is obviously not co-planar with the lathe spindle or chuck.

Solution... Make the tailstock rotate in the same plane as the spindle. Perhaps an accurate faceplate on the spindle and a faceplate on the tailstock. If there is any misalignment at all fix it. The smaller the misalignment the greater the reduction ratio.

See... math to the rescue.

clint

[Dale Miner]

It is caused by a misalignment between the two rotating axis. As the cone rotates the slight clearance in the threads allows the cone to slowly walk as the misalignment applies an uneven loading to the cone as it rotates.. In this case it just happens to walk towards the headstock. If you run the lathe backwards, it will likely cause the cone to screw onto the center.

A possible solution would be to turn a plug with a shoulder that fits snug into the open end of the cup, and use the lathe center to hold the plug in the cup and provide support for the turning. ( no cone needed)

Another possible workaround would be to put the cone in the open end of the cup and apply a slight bit of pressure with the hand wheel. Then with the lathe running about 150-200 rpm, reduce the clamping pressure that holds the tailstock to the bed until you can crank the hand wheel and move the tailstock backwards about 1/4 inch with the lathe spinning. Sometimes this will allow the sideways misalignment to correct itself when the tailstock is moved. If you have a sliding headstock, try the same method to slide the headstock. I have done metal spinning demos where the misalignment was enough to cause a piece of metal to walk even though the clamping force between head and tail stocks was very strong. Allowing both head and tail stocks to 'self align' this way corrected the problem.

If the piece was put between a center in the headstock and the cone in the opening, it is doubtful you would see the cone unscrew. The misalignment would be absorbed at the ends of the drive center and there would be very little force left to cause the cone to unscrew.

[John K Jordan]

As mentioned earlier, I'm an advocate of using a wooden support piece (with a shoulder) to hold such a piece.

However, you bring up a good point about the alignment - even if it's not the problem here the centers on a lathe should be aligned. This is usually a simple process and only takes a moment. For those who haven't checked the alignment, simply put centers with central points into both the headstock and tailstock and slide the tailstock close to the headstock. The points should be touching. Typically, if out of alignment one point will be closer to you than the other. The fix is to adjust one leg of the lathe by cranking up on the leg leveler, or by adding a shim if there is no leveler. I usually raise one of the front legs since they are easier to reach - if the tailstock point is closer towards me I raise the front right leg until the points align. (It might seem odd but cast iron lathe beds are flexible and will easily twist.)

I check the alignment EVERY time I move a lathe, even if moved only a few inches since even then it can be forced out of alignment unless the floor is dead flat. When Mark StLeger came to the Knoxville turning club last year the club Jet 1642 was terribly out of alignment and caused a problem for him. When we took a break I checked the alignment and fixed it with a slight turn on one leg leveler.

If the misalignment is in the vertical plane, that's a different problem. I've never seen that.

JKJ



It is caused by a misalignment between the two rotating axis. As the cone rotates the slight clearance in the threads allows the cone to slowly walk as the misalignment applies an uneven loading to the cone as it rotates.. In this case it just happens to walk towards the headstock. If you run the lathe backwards, it will likely cause the cone to screw onto the center.
...

[Leo Van Der Loo]

As the OP says, the centers are aligned and there is no slop in the thread of the cone and center, then the previous reasons are not logical.

But as I mentioned before chatter could cause this, where the wood is flexing and rotational going back and forth, grabbing the cone in the forward direction just so slightly, thereby rotating the cone and loosening it off.

A tight wooden cone could help in preventing this I do expect.

[Michael Mills]

Ok, time for my stupid question.
If you are using carbide they MAY cut so... are you turning in reverse?
Told you it was stupid but no one else asked.

[daryl moses]

Ok, time for my stupid question.
If you are using carbide they MAY cut so... are you turning in reverse?
Told you it was stupid but no one else asked.
LOL, I was going to ask the same question but was afraid I would offend the OP. I even wondered if he was standing on the wrong side of the lathe.:rolleyes:
I suppose the live center could come loose but for the life of me I just can't see how.

[Michael Mills]

Well I thought of it because I have done it a couple of times when I forgot to switch back after sanding. The first time I even re-sharpened my gouge because all I could get was little chips.
But I did remember that here (or a different form) recently two folks posting that their lathes came with the switch reversed... or if it read forward it was really reverse and...

[Clint Bach]

Aligning the tips point to point does not definitely mean the axes ( plural of axis?) are aligned. If the axes of rotation are not aligned they are out of alignment even if the tips of the centers are exactly touching. An extreme example is if the tailstock and the headstock were at ninety degrees to each other the tips could touch perfectly. Would they then be aligned? Absolutely not! Assuming the axes could be even slightly misaligned on their axes of rotation (not just point to point) the above reasons can hold true. I don't know how to test for that...

Another solution to the cones unscrewing could be to put less pressure from the tailstock therefore allowing a slight bit of wiggle. Using just enough pressure to make the spindle run true may solve this problem.

if you try that report back.

Clint

[Leo Van Der Loo]

Aligning the tips point to point does not definitely mean the axes ( plural of axis?) are aligned. If the axes of rotation are not aligned they are out of alignment even if the tips of the centers are exactly touching. An extreme example is if the tailstock and the headstock were at ninety degrees to each other the tips could touch perfectly. Would they then be aligned? Absolutely not! Assuming the axes could be even slightly misaligned on their axes of rotation (not just point to point) the above reasons can hold true. I don't know how to test for that...

Another solution to the cones unscrewing could be to put less pressure from the tailstock therefore allowing a slight bit of wiggle. Using just enough pressure to make the spindle run true may solve this problem.

if you try that report back.

Clint

You have a point Clint in the alignment, I was assuming a normal straight lathe bed would be good for alignment, but then again some china stuff isn’t always so precise ;-)

[Kyle Iwamoto]

Aligning the tips point to point does not definitely mean the axes ( plural of axis?) are aligned. If the axes of rotation are not aligned they are out of alignment even if the tips of the centers are exactly touching. An extreme example is if the tailstock and the headstock were at ninety degrees to each other the tips could touch perfectly. Would they then be aligned? Absolutely not! Assuming the axes could be even slightly misaligned on their axes of rotation (not just point to point) the above reasons can hold true. I don't know how to test for that...


I'm sorry. This is absurd. The way a lathe is built, there is absolutely no way for the axes to be other than in line. 90 degrees off? I don't think so. I see what you are saying, but it does not apply. It the points line up they SHOULD be colinear. I think, in my opinion they must be, but I could be wrong. A very simple test.
Well, I guess that if your lathe bed was WAY crooked, you may have a point.

[Mick Fagan]

I think Clint Bach has a valid point. Alignment of the tips does not mean the head stock spindle and tail stock quill, are running in an exact straight line.

If you check your alignment with the tail stock quill fully retracted, then move the tail stock rearwards to allow you to fully extend the quill, it is reasonably probable a slight discrepancy may show up when the quill is fully extended. If it isn't exactly the same when fully extended compared to when fully retracted, then the head stock and tail stock are more than likely not parallel.

My turning club has an issue with one of our lathes, sometimes when doing spindle work one can get a vibration, a quick check as above will sometimes show a minute misalignment which we can shim out. Mainly due to having a swivel head and the fact that the lathe has been used up to six days a week by every dog and his body over the last 10-12 years.

Also, page 36 of the Laguna Revo 24/36 manual, mentions exactly this and how it is best to re-align the head stock to match the tail stock and why. They have a facility, built in, to allow accurate centre point alignment either by adjusting the head stock, or tail stock.

The Laguna 24/36 manual, is available online for those who would like to peruse that document.

Mick.

[John K Jordan]

Aligning the tips point to point does not definitely mean the axes ( plural of axis?) are aligned. ...

This is true. Unfortunately we have little choice but to accept that the ways of the bed are straight and the headstock and tailstock are machined within tolerance. If well machined, removing any twist in the bed will align the entire lathe. If this is not true, get a better quality lathe. (I think alignment is important when one end of the work is held firmly, say, in a chuck, as opposed to a spindle is held between centers.) If holding the free end of a piece with the point of a live center you can assure the point is aligned at that specific distance: with the piece mounted firmly in the chuck spin the wood and mark the center at the end, then bring up the point and see if it is aligned with that mark.

I do wonder about lathes like the Nova which allow pivoting the headstock away from alignment with the bed. I've never used one so I don't know how easily alignment can be compromised. Since Nova offers a double-ended MT alignment tool "to check and correct the alignment" I'm assuming perfect alignment is not assured without it.

I've considered ways to check the alignment of the headstock and tailstock of any lathe. I have a laser center finder I use with my milling machine: https://littlemachineshop.com/products/product_view.php?ProductID=2604 If I mount this in a collet in the wood lathe headstock, the beam will be directly down the lathe bed. If the finder and mount are perfect the red dot will stay at one point when the lathe is rotated by hand. If slightly out, the rotation will describe a circle, the center of which will be the axis of the headstock. The alignment of the headstock with the bed could be checked with precision by moving a target on the tailstock to different positions. Mounting the same center finder in the tailstock could check to see if the axis of the tailstock was properly aligned with the bed. (All bets are off if the headstock spindle or quill machining or the are off or the headstock/tailstock themselves are poorly made.)

BTW, something which can throw off the alignment of a lathe is a bit of dust or other material in the MT sockets or on the mating surfaces between the chuck and spindle. Chris Ramsey (who turns cowboy hats) said he always cleans the dust spindle and chuck before mounting and especially when remounting a chuck. I try to remember to regularly clean the MT sockets with one of these https://www.woodturnerscatalog.com/p/90/3651/TaperMate-Morse-Taper-Cleaner Perhaps the worst thing for the lathe spindle is if the inside is scratched or galled leaving a burr. This can happen if something allows a taper to spin when mounted, especially if the spindle is not hardened as in some lathes. Fortunately you can feel this if your finger is small enough and fix it - I had to do that on one lathe.

Regardless of the type of axial misalignment Clint describes, I still think the OP's problem can be eliminated by replacing the cone with a short snug cylinder with a shoulder, a "plug" as someone well described it. Bring up the tailstock while the piece is spinning to support this plug. If the point of the live center is aligned with the center of rotation at that point, all should be well, even if the overall alignment off.

JKJ

[Dale Miner]

Even IF (big if) the bearing bores are perfectly in line with the guides on the bottom of the headstock, and IF the quill bore is bored perfectly in line with the guides on the bottom of the tailstock, and IF the bore in the quill is perfectly in line with the OD of the quill, and IF the axis of the quill and the axis of the head and tailstock are at exactly the same distance above the bedways and IF the axis are on exactly the same horizontal plane, there is still some clearance between the guides on the bottom of the headstock and tailstock and the bedways.

If that clearance is only .002" and the distance between the guides is 6", then it is is possible to have a .002" parallel offset if both guides are against the same side of the bedways. The situation is much worse if one guide block is against one side and the other block is against the opposite side. This could lead to an angular misalignment of as much as .0007"/inch.

At the end of a 6" long cup that yields over .004" misalignment. And, the big IFs mentioned above are very likely to not be perfect.

Regardless the amount, be it .004" or more likely as much as .04", the loading on the cone will not be uniform. There will be a greater force at some position of rotation. That position will remain in a fixed phase of rotation.

The pitch diameter of the male threads of the center and the pitch diameter of the female threads in the cone are not exatcly the same. There must be some clearance for the two to easily assemble. If the clearance is only .002", then the difference in the two pitch diameters is .002"x pi, or about .0066"

The uneven loading causes the smaller male thread to turn ever so slightly faster that the larger female thread. Each revolution requires the smaller male thread to make up that extra .0066" by advancing a few degrees.

Imagine putting a 12" diameter wheel inside of a 13" diameter hoop with the wheel setting on the bottom of the hoop.

If you turned the 13" diameter hoop one revolution, the wheel would turn 1.125 revolutions.

This is what is happening between the male thread on the center and the female thread of the cone. I have seen it happen often on my and other lathes.

[Dale Miner]

Aligning the tips point to point does not definitely mean the axes ( plural of axis?) are aligned. If the axes of rotation are not aligned they are out of alignment even if the tips of the centers are exactly touching. An extreme example is if the tailstock and the headstock were at ninety degrees to each other the tips could touch perfectly. Would they then be aligned? Absolutely not! Assuming the axes could be even slightly misaligned on their axes of rotation (not just point to point) the above reasons can hold true. I don't know how to test for that...

Another solution to the cones unscrewing could be to put less pressure from the tailstock therefore allowing a slight bit of wiggle. Using just enough pressure to make the spindle run true may solve this problem.

if you try that report back.

Clint

Clint,

You could "test for that" by using a double reverse indicator method (after allowing for indicator sag), or by using some relatively expensive laser alignment equipment. I have used both methods, the laser is far and away the more accurate.

[Kyle Iwamoto]

Imagine putting a 12" diameter wheel inside of a 13" diameter hoop with the wheel setting on the bottom of the hoop.

If you turned the 13" diameter hoop one revolution, the wheel would turn 1.125 revolutions.

This is what is happening between the male thread on the center and the female thread of the cone. I have seen it happen often on my and other lathes.

An interesting and awesome explanation! Thanks! And I thought it was only me that seen this..... I was in denial, HUH? Am I seeing things? This can't be happening, did I tighten that down? Kept happening......

[Hayes Rutherford]

What Dale said.

[Bill Boehme]

Is there any vibration while turning the wood? Vibration combined with Dale's thoughts, and a tailstock that creeps can be enough for the cone to work loose. My first lathe had a Reeves drive and the vibration that it created was sufficient to cause everything to rattle loose ... tailstock, banjo, toolpost lock, headstock. I apologize if this idea has already been kicked around.

[Len Mullin]

Ricc,is the live center and cone both, made by the same company? if not, that could lead to your issues. Or another possibility, is the cone and live center the same thread? Could one be metric, and the other be imperial? I have a hard time believing this could happen, but you've stated that it's happened with your buddy's live center as well as your own. So, it's obviously happening, but I be darned if I can envision how with the threads being as they are.
Len

[Ricc Havens]

Ricc,is the live center and cone both, made by the same company? if not, that could lead to your issues. Or another possibility, is the cone and live center the same thread? Could one be metric, and the other be imperial? I have a hard time believing this could happen, but you've stated that it's happened with your buddy's live center as well as your own. So, it's obviously happening, but I be darned if I can envision how with the threads being as they are.
Len

Same Manufacturer and same thread. No tailstock creep. No vibration as I am turning. The bearings in the live center are good and not dragging. A lot of good thoughts have been shared and I thank you all for your input. I ahve tried a couple of the suggestions (like the plumbers tape, checking alignment, etc). I can't afford a Nova live center as John K.J recommended as I'm on disability. But, I will try a couple of the other suggestions like turning a wood cone that Leo suggested, and maybe trying to find someone to drill and tap the aluminum cone for a set screw.

Keep ideas coming if you think of anything else.

Thanks
Ricc

[Joe Kaufman]

Try checking the run-out of the aluminum cone and live center. Put a short dowel, wood or metal, in the live center to lock it. Install the cone and place the assembly in the spindle taper. Run the lathe to check the run-out of the cone surface. This process can be used to true up the surface if required. Use a cutoff tool or a round nose scraper that will limit the width of the cut.

If you make a wood cone, use this process for the final true-up of the cone.

Note : You should verify that the center point of the live center runs true in the lathe spindle before checking the cone run out.

[Ricc Havens]

Try checking the run-out of the aluminum cone and live center. Put a short dowel, wood or metal, in the live center to lock it. Install the cone and place the assembly in the spindle taper. Run the lathe to check the run-out of the cone surface. This process can be used to true up the surface if required. Use a cutoff tool or a round nose scraper that will limit the width of the cut.

If you make a wood cone, use this process for the final true-up of the cone.

Note : You should verify that the center point of the live center runs true in the lathe spindle before checking the cone run out.

I will give it a try Joe. Thanks for the suggestion!

Ricc

[Phil Anderson]

I know this is an older thread but because I'm experiencing the same thing, I went a googling and found this conversation. I DO have a Oneway. I'm not using the larger cone, just the smaller cone that came with it. I've inserted the rod and use hand tightening, with a non-slip glove on. After awhile, the cone begins to screw itself off the threads. It is usually preceded by a noise, grinding, maybe a little squealing. I'm mostly a bowl turner but it has happened with spindles as well. I might get 6-7 pieces done before it happens, maybe more, but it happens. I don't get it! I will be contacting Oneway, but just wanted to toss this into the mix. Ricc Havens, any solution found?

[Bert Delisle]

Have you tried making a wooden cone/jamchuck support that can be threaded onto the live center. It could be sized to just fit the mug bore for support with little pressure.

[Ricc Havens]

Phil, I still have the problem.

[Karl Loeblein]

I wonder if a flat ribbed or a copper crush lockwashers (not a split washer) might keep the cone from backing off without resorting to Loctite.

[Marvin Hasenak]

I made these a different way, I first drilled and cleaned out the inside as above. I made a plug that fit the inside of the hole that was threaded on to the lathe spindle. The blank was slid on the plug and then turned, I used a regular live center to keep the blank from sliding off the plug.

Basically the wood plug worked as a jam chuck to hold the blank. Drill and tap a 3x3x10 blank and screw it on the spindle, turn to inside diameters of the cup blank. The only parts of the plug that were critical were the bottom diameter and the top diameter. I also cut a 1/4" wide groove top to bottom to prevent any vacuum suction problems.