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.
Member
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.
Contributor
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?
Member
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.Originally Posted by Paul Williams
[OP]
Contributor
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
[OP]
Contributor
Kyle, I do use the rod that came with it to tighten but still have the problem.
Ricc
[OP]
Contributor
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
I
[OP]
Contributor
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
Moderator
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-Cen.../dp/B0064JIZGC
JKJ
Member
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.
Member
Do you want the number for Madam LeDouche in New Orleans maybe yeah.
Member
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.
Member
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.
Member
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.
Member
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
Contributor
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?
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