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Adjustable jam chuck for spheres

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I have turned 30 or more spheres in the last couple of weeks for a coat rack, and just to turn them and use up some scraps. I keep thinking back to Allan Batty and him commenting about turning billiard balls out of elephant ivory. It was a couple of years project, but final turning was with a jam chuck. In trying to get a 'nearly perfect' off the tool sphere, I am coming close. I did discover that live centers can be highly variable for any kind of accuracy, and ended up using an old Nova Center where you could knock the tip out and use a new one. I was able to chuck it up in my chuck, and rough turn a cup chuck for it, but that was still off a bit. I put the head of a cordless drill on the live center, while it was in the tailstock, to spin it while I trued up the cup with a NRS. That got me very close, but not quite to the point where I couldn't feel ridges that would have to be sanded off. So, I need to find some sort of 'adjustable' jam chuck to finish off all of my spheres, and maybe get a tooled final cut where I can find no ridges. Anyone have any suggestions? I am thinking extended chuck jaws with a softer plastic that will flex for a secure grip that won't leave marks. I don't particularly want to have 50 different jam chucks, and none of my spheres are the same size, even if I start out with the same sized blanks.... Maybe some of the white plastic and turn it true? There has to be some sort of solution. Maybe one of the chucks they use for bowls that are actually round, and you screw/twist it till you get a secure grip? Is that a Longworth chuck?

robo hippy
 
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I have turned 30 or more spheres in the last couple of weeks for a coat rack, and just to turn them and use up some scraps. I keep thinking back to Allan Batty and him commenting about turning billiard balls out of elephant ivory. It was a couple of years project, but final turning was with a jamb chuck. In trying to get a 'nearly perfect' off the tool sphere, I am coming close. I did discover that live centers can be highly variable for any kind of accuracy, and ended up using an old Nova Center where you could knock the tip out and use a new one. I was able to chuck it up in my chuck, and rough turn a cup chuck for it, but that was still off a bit. I put the head of a cordless drill on the live center, while it was in the tailstock, to spin it while I trued up the cup with a NRS. That got me very close, but not quite to the point where I couldn't feel ridges that would have to be sanded off. So, I need to find some sort of 'adjustable' jamb chuck to finish off all of my spheres, and maybe get a tooled final cut where I can find no ridges. Anyone have any suggestions? I am thinking extended chuck jaws with a softer plastic that will flex for a secure grip that won't leave marks. I don't particularly want to have 50 different jamb chucks, and none of my spheres are the same size, even if I start out with the same sized blanks.... Maybe some of the white plastic and turn it true? There has to be some sort of solution. Maybe one of the chucks they use for bowls that are actually round, and you screw/twist it till you get a secure grip? Is that a Longworth chuck?

robo hippy
I always use a pair of wooden cups lined with O-rings, this allows me to hold the sphere in any orientation for sanding to achieve a perfect ball.

Hope that helps

Richard IMG_4039.jpeg
 

hockenbery

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I use a cup on the headstock and a 1/2” leather covered flat on the tail stock. I learned this from Christian Burchard
Rotating the spheres through the 3 as is while turning and sanding will get you a near perfect sphere

Sometimes the turning requires going through the 3 axis twice.
In a demo at SWAT I messed up. Put the ball in to turn and it was totally round from 2 axis.It happened every once in a while but never in a demo. Had to apologize for overachieving.

A ring on the spheres will show any out of round by not laying flat
 
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hockenbery

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Reed, The drive cup should be about a 1/3 the diameter of the sphere. A little less is better than a little more.
It’s a trade off between holding power and working room on the sphere.
A 1/3 lets you work an area round to sit in the cup.

The pdf shows the ball in the cup process.

You can see the process
 

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That’s a neat idea Richard. What sort of stock sizes of O rings do you keep, and any cheap sources of supply?
I think I got a mixed box from Screwfix and for the bigger ones I went to my local bearings supplier who have them in all sorts of sizes. I have a set of blocks with 25mm and 40mm O-rings for different sized balls. I’ve done up to 8” balls on the 40mm set
 
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Well, I did try some neoprene O rings, and the problem I had with them was that they would not seat the sphere well, and could move once I started turning. I also tried some 3/16 thick cork, and again problems with not seating true. I may need to do my morris taper cup over to get a better fit. It seems to need to be trued up a tiny bit every time I use it.... I am hoping to get billiard ball round. Not sure that is possible with cup chucks. More experimenting ahead.... My cups are in that 1/3 diameter range, so that is good. I have been thinking about a piece of felt or some thing similar as 'padding' and some thing to drive the sphere, and hopefully not burnish the spot where it seats. I did find that when seating the sphere, if I use finger pressure to seat it against the headstock cup, that can center it almost perfectly. I kept ending up with 3 sides equally spaced from the tool rest, but the 4th side was way off, like 1/16 inch on a 1 1/2 inch sphere. That lead me to making a new tailstock cup. I got one the other day that had maybe 1/32 ridges on it, and that was the best by far. Much better than the 1/16 or so I was getting, I just want better.... I think that is the advantage of the jamb chuck that Allan was talking about. For billiard balls which had to be exactly the same size, you could have several which would take you through the different turn downs. Well, more experimenting ahead!

Oh, I do go through the rotations several times. In theory, 3 times should work, but I am not that good yet. Had a piece of Mountain Mahogany on and went through the rotations maybe 10 times. It kept getting closer and closer, but not there, yet....

robo hippy
 

hockenbery

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Well, I did try some neoprene O rings, and the problem I had with them was that they would not seat the sphere well, and could move once I started turning. I also tried some 3/16 thick cork, and again problems with not seating true.
I have found bare wood works about the best. I do my cups in mahogany or soft maple. Woods that are softer than most of the balls I turn. I have used some of my vacuum chucks with fairly stiff fun foam to turn large diameter balls 10”.
I want to avoid a spongy drive cup.


Rubber Chucky has the cups for head and tail in rubber. I would think the smaller set would turn any size.
The rubber chucky cups are great. I was one Don Doyle’s guinea pigs. Don was in our club when he was just starting the rubber chucky. He’s a master at mixing the materials to get the hardness soft enough to grip and not mark and hard enough not to be spongy. Sort of like mahogony is.
I tested about 4 cups before Don got the mixture right.
The first was so soft I didn’t even put it on the lathe. One was too hard, then a tiny bit spongy, then perfect.

I use the cup sometimes but use a soft point on the tailstock. I had to modify one of Don’s points.
IMG_1086.jpeg

This is a mahogany cup on a hard maple Morse taper
IMG_1089.jpeg
 
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I did use Ipe for the headstock cup, and turned a Morris taper on it. It is starting to split out, so I have to make another one. I did have one for my small chuck, and that worked pretty good as well, but the MT one is easier to put on and take off. Will look up Rubber Chucky. I did mark the chuck one with the #1 jaw so it should go on exactly the same way every time. I looked at one of the sphere cutting set ups, and just thought no, I can do it fine without the jig. Not difficult if you do enough of them. I remember Soren Berger had a jig set up for kind of turning an octagon then rounding the edges over. It worked, but I don't want no jig.... I have been trying to figure out how to make a 45 degree angle jig to check the first 2 sections of the octagon.... New challenges!

robo hippy
 
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Urethane O-rings might be better than rubber.

We use the stickiness of urethane to advantage when press forming metals. Pretty amazing stuff. I've never done anything with wood and urethane but with metals it works magic.
 
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Urethane O-rings might be better than rubber.

We use the stickiness of urethane to advantage when press forming metals. Pretty amazing stuff. I've never done anything with wood and urethane but with metals it works magic.
While not exactly the same, I 3D print vacuum chuck rings in thermoplastic polyurethane (TPU). I can use different shore hardness and printing parameters to achieve different levels of squish, such as slightly softer for vacuum applications or harder if I am just using it as a jam chuck. Unlike silicone, it doesn't leave any markings on the wood, and unlike setting urethane in molds, it is very easy to use!
 
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I have been watching a number of videos on sphere turning, and there are a lot of variations.... The one that cracks me up are those who start off turning a sphere by just eyeballing it. You have to have some experience to get that close. Not for the average beginner....

Kevin, that stuff looks interesting. May have to try some, but I do need to find a piece I have in the shop. Maybe 1/16 or slightly thicker material. A number of videos recommended using some felt in the cup chucks. The quest continues!

robo hippy
 
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I’ve seen some very skilled turners produce a sphere in no time at all. I happen to like making tools so I made my own sphere jig.
Takes me at least ten times as long to make a sphere but I kind of like the process.
 

hockenbery

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have been watching a number of videos on sphere turning, and there are a lot of variations....
You need to stand next to Michael Hosulak while he turns a ball with a skew with two tiny nibs left between centers which he cuts of with a pocket knife and sands smooth.
Most of the time he’s carrying on a conversation about something totally unrelated to the ball.
 
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And then Michael Hosaluk will turn it into a baseball with pyrography stitching all freehand. There a number of these in a display case at Marc Adams School of Woodworking all signed by Michael and the students in the class.
 
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Okay, I did see some one, who made a threaded jamb chuck that went onto a Oneway live center. Anyone know about thread cutting stuff for that? Also, some one I have been chatting with said that you can put a pin through the live center so it does not spin, and then I can put that into the headstock and turn a cup that should be spot on when I put it in the tailstock.... Sounds like a good idea...

robo hippy
 

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Okay, I did see some one, who made a threaded jamb chuck that went onto a Oneway live center. Anyone know about thread cutting stuff for that? Also, some one I have been chatting with said that you can put a pin through the live center so it does not spin, and then I can put that into the headstock and turn a cup that should be spot on when I put it in the tailstock.... Sounds like a good idea...

robo hippy
Putting a pin or screw thru the live center hole is one way to true up a wood live center adapter. When I've done that, I always wrap the live center in elec tape to capture the pin/screw - just in case.
More often, I will epoxy a nut in a blank to screw on the live center 3/4"-10 for the oneway and its clones). Sometimes it's not a nut but just a 3/4" hole to seat over the threads. Or you could tap it with a 3/4 tap. I use the nut when I want something more secure that should run truer. Either style needs to bottom out on the face of the live center (not the cup or tip, but the flat below the threads).
I'll screw it on, put it in the tailstock and jam it against the spindle or a chuck etc. Then I turn a small tenon on the back side next to the nut. Chuck it to turn whatever profile I want. And I can re-chuck it anytime I want to re-profile it.
 
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Years ago I bought a dozen large nuts that fit my spindle to make various fixtures. I think that is easier and cheaper than finding the right sized taps. Epoxy them into a chunk of wood and turn them true.
 
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Okay, I did see some one, who made a threaded jamb chuck that went onto a Oneway live center. Anyone know about thread cutting stuff for that?

robo hippy
I bought a 3/4” tap from Amazon (about $10). Creating various shapes for the live center is quick and easy - Tap a block of wood, then put a short end of 3/4” all thread in the chuck, screw on the tapped piece of wood and shape it to your desired configuration.
 

Tom Gall

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Okay, I did see some one, who made a threaded jamb chuck that went onto a Oneway live center. Anyone know about thread cutting stuff for that? Also, some one I have been chatting with said that you can put a pin through the live center so it does not spin, and then I can put that into the headstock and turn a cup that should be spot on when I put it in the tailstock.... Sounds like a good idea...

robo hippy
What @Dave Landers said. I bought a half-dozen or so 3/4"x10tpi nuts from Lowe's many years ago. Should be available at most big box and hardware stores. IMO, a lot easier than buying and using a tap - and reusable if necessary.
 
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Tom Gall

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@GRJensen Nice tip from Lyle ... but unrelated to the topic. We're talking about a pin through the live center mounted in the headstock (not the quill in the tailstock) so as to turn an adapter to your desired shape.
 
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FYI - the Robust cup/drive/safety center is threaded 3/4" - 10 tpi so you could use that to turn the profile you wanted for the live center. You could obviously also use this to drive the sphere as well. I really like using this cup center for spindle turning, catches are never disastrous when I use it..
 
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