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Turning a sphere

  • Thread starter Thread starter mkart
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mkart

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Anyone know where I can find an article for turning a sphere. I would like to turn a few locust spheres that end up the same, or similar, but need help in shaping and chucking. I am going to cut out a template and compare as I turn for now. I just can not seem to get a ball that is remotely round. A 5" sphere ends up a 1" oval by the time I'm done.
Thanks
mkart
 
There are several articles on turning a ball in my different magazines and books. I'll have to dig them up to give you references. Basically turn a ball shape with a tenon on each end. Just get it as close as you can. Then make what they call cup chucks. One for the headstock and one for the tailstock. These are wooden shapes that have a concave area to be pushed against the ball shape and hold it while it spins.
You rotate the ball 90 degrees and turn away the shadow. Then rotate it 90 degrees in a different axis and do it again. Keep doing this until it's perfectly round. Of course you may start with a 6" ball and end up with a 1" but it will be round.
Another way is the Brian Simmons showed me. You have to turn the ball as close to round as you can. Then you use a scraper to get rid of the high spots. To find these you take a flat ring and move it around the ball. You will very quickly see the low spots when light passes under the ring. Scrape off the high spots and check again. Another friend took the lens out of a flashight and slides it around the ball. The light leaks under the low spots.
The best method I've seen which I think is in one of Mike Darlow's books and is often demonstrated by Mark StLeger is to use a rotating scraper. It is a fairly simple device that you attach to the bed of the lathe. You rotate it around the ball and cut a little off. Then slide the cutter forward and do this again. You still have to use a cup chuck or vacuum chuck to turn off the little tenons left on either end but this method gives you balls that are exactly the same size.
when I get home tonight I'll check here and if no one has posted a web site that shows how to make a ball I'll dig up some of the articles.
 
Ball cutting jig

Mr. Lucas, I am familiar with the jig you mentioned. I made one for my metal lathe, which is not usable with a wood lathe. One of my current projects is to design and build a jig that can be attached to the bed of a wood lathe. It will be adjustable for a range of sizes.

Unfortunately, I have to complete work on a couple other projects. One is the spindle and parts for a Rose Engine. Another is a cutting frame for ornamental cutting. Until I complete my retirement these will go kind of slow. I can only work on them on Saturday mornings.
 
I use geometry

I have some notes I used in an Intermediate woodturning course. Using this method you can get within an 1/8 inch or so of a specific diameter fairly easily.

http://www.hockenbery-woodturnings.com/SphereDescription.pdf

You may find them useful. The idea is turn an cylinder the diameter of the ball you want. Then part in at the ends the cylinder the length of the diameter. In cross section you have a square. cut off the corners and in cross section you have an octagon. cut off thes corners and you have a sphere with lots of flats. At this point all you have done is cut straigt lines. Round the flats and you almost have a sphere except for the nubs at the centers.

The neat hing about this method is that you can turn a spherical section on something.

Also one of the Springett books has a Sphere cutting jig. It works sort of like a duplicator. it is a cutting bit mounted in a block of wood that is set to pivot on the ways of the lathe. By swinging it back and forth you get a sphere of a diameter determined by the pivot point. Maybe some one has this book an can relate the specific title.

-Al
 
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thanks

Thanks to everyone for the info. I printed the article and may pick up the book you mentioned. I hope to try this weekend. If I succeed I will post some photos.
mkart
 
MKart
I watched Christian Burchard turn a ball this weekend. He does it basically the same as the article. What He did that I thought made a lot of sense, was when you have rotated the ball and are turning away the shadow, don't ever turn so that you get a complete shaving all the way around. Take little cuts and stop and check and when you have remove all but 1/2" or so of the old wood stop and rotate the ball to the next axis. He draws a line on each axis so that when you rotate the ball you can see the line.
If you make a cut that goes all the way around you have to reduce the size of the ball and you will keep getting the shadow of the old shape that must be removed and the ball gets smaller and smaller. Been there done that so I know he's right.
I think He's the one who wrote the article in a past issue of American Woodturner.
 
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