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Adjustable jam chuck for spheres

R

robo hippy

Joined
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Eugene, OR
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
 
robo hippy said:
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
Click to expand...
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
 
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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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

Ball in a Ball

A ball in a ball is great fun. People try to figure out how? In the demo video I show how to turn a ball, hollow it to receive the smaller ball and then pop the smaller ball through the hole. There are also links to handouts I use in demos. dogwood large ball about 3” I got the idea for...
www.aawforum.org www.aawforum.org
 

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Bill Alston said:
That’s a neat idea Richard. What sort of stock sizes of O rings do you keep, and any cheap sources of supply?
Click to expand...
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
 
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
 
robo hippy said:
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.
Click to expand...
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.


Rusty Nesmith said:
Rubber Chucky has the cups for head and tail in rubber. I would think the smaller set would turn any size.
Click to expand...
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
 
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.
 
Doug Rasmussen said:
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.
Click to expand...
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!
 
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
 
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.
 
robo hippy said:
have been watching a number of videos on sphere turning, and there are a lot of variations....
Click to expand...
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.
 
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
 
robo hippy said:
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
Click to expand...
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.
 
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.
 
robo hippy said:
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
Click to expand...
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.
 
robo hippy said:
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
Click to expand...
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.
 
@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.
 
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..
 
Well, not there yet, but getting closer.... Just turned a sphere that I was able to sand out starting at 180 grit. Some 'conclusions' for now. ANY type of padding on the headstock chuck reduces your accuracy of remounting the sphere when you rotate on the 3 axis ideal. I had tried some thicker cork, way off. I tried some felt, still pretty far off. I may go back and try an O ring again, but maybe not. I did make one big change to my drive cup chuck, and made it about 1/3 the diameter of the sphere I was turning. That made a huge difference, and that was the sphere that I was able to sand out starting at 180. Not sure if making it even bigger would be much of a help or not. That would mean making the tailstock cup chuck much smaller, which would end up being almost a jamb chuck. This has made me wonder about a vacuum chuck, which I don't have. I would need an O ring for a good seal, at least for the first couple of series of 3 axis rotations, and as I have said, any type of 'padding' on the drive chuck seems to mean less accuracy for remounting to get to 'perfectly' round spheres. The quest goes on!

robo hippy
 
robo hippy said:
... I have been trying to figure out how to make a 45 degree angle jig to check the first 2 sections of the octagon....
Click to expand...
I’ve just found this thread so forgive me if my response to this challenge is something you’re way past. To test the 45° sides of the turning I use a combination square with the angled portion held against the side of the turning. If the ruler comes out perpendicular to the lathe bed/axis of rotation, I’ve hit the 45° angle. With the ruler extended all the way out, it’s easy to see if you are spot on or not.1709509861888.jpeg
 
robo hippy said:
ANY type of padding on the headstock chuck reduces your accuracy of remounting the sphere when you rotate on the 3 axis ideal. I had tried some thicker cork, way off.
Click to expand...
Glad tour getting better results.

I’ve been using a plain wood with great success since my class with Christian Burchard in 1998 or so.
Soft maple or mahogany are softer than most balls I turn.
When I do camphor balls i notice the cup leaves light compression lines during sanding.
These disappears with 320.

I’ve used this same set up in lots of classes and club workshops. A few students have burned a ring. Usually - tailstock too loose or tool rest too close.

Plain mahogany cups no padding. I use leather glued on the 1/2” diameter tail center.
The one on the right still has the nubs from to turn off the fuzzy Pat to get the sphere
IMG_1251.jpeg……………IMG_1250.jpeg
 
I did try a mini tri square to check for that first 45 degree cut, and it kind of worked. I would make sure the tool rest was pretty parallel to the lathe bed, and put the square on the tool rest. It was okay. Finally last night, I cut a piece of 1/8 inch plywood to 45, and 90. It ran a bit long, so I put the bevel side on the face, and measured how far off it was by how it went across the top of the sphere.

Another thing I tried yesterday was remembering an old trick I had tried but forgot about. You need 3 axis rotation for turning your sphere on. The old trick was to put an equator on, rotate, then turn down to that pencil line, but DO NOT remove that line. That got things much closer.... Ongoing!

robo hippy
 
I tried my hand at spheres a few years back to no avail. At the time I started turning a cup and using that to hold the sphere. At some point, after tripping over my son's skateboard it hit me to use the skate wheels as a jam chuck. The poly is soft, so no marks and uniform. I suspect you could turn the wheels on the lathe to adjust the size, but I didn't try it. Then again, maybe using the wheels is why I didn't have much luck turning spheres. 🫤image_50398721.JPGimage_50398721.JPG
 
In "theory" you should be able to get a "perfect" sphere in one set of rotations. Yesterday, I got one that was close to billiard ball round after rotating through the 3 axis pencil lines maybe 10 times. It seems that it takes a couple of revolutions of the different rotations before I get to the point where I don't take out any of the pencil lines.

The skate board wheel idea seems pretty good. May try it some day, but haven't been on anything like them in 30 years. I am too old and brittle....

robo hippy
 
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