Replies

1. 
   JohnWW | Jan 19, 2004 07:53pm | #1

   Loren,

   The 36 inch dimension isn't a typo?  Even hollowed out that would be a very heavy piece. 

   Once you get past the diameter that can be turned from a solid block of wood, half of the  problem becomes gluing up the rough sphere.  The classic way to make the blank is to build it from blocks stacked like bricks, starting on a small base disc and building up the bricks in ever widening circles to create a bowl shape.  Make two bowls and then glue them together to make the ball.

   An elegant solution to building the sphere would be to use five and six sided blocks glued up like a geodesic dome or a soccer ball to create the blank. 

   Large balls are usually shaped with a jig swinging a router in an arc as the cutting tool, I've seen them described a few times over the years, perhaps someone can recall an article or two and post it here.

   John W.

   
   

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   Edited 1/19/2004 5:51:16 PM ET by JohnW

1. 
   Loren | Jan 19, 2004 08:14pm | #2

   Yes, I did indeed mean 36" and yes it would be heavy indeed! I get the part about glueing up, but how to make it smooth enough to roll precisely is the tricky part. Did you mean a pin router? I just cant invision a swinging arm thing with router attached...what would keep it running true? Thanks for your response.....loren

1. 
   BenM | Jan 19, 2004 09:32pm | #3

   FWW had an article a long time ago about making a globe.  It was made of two hemispheres and each hemisphere was made of about 20 "slices".  These slices looked like something you would cut from a melon.  Smoothing out the surface will be the hard part; even a small globe has several square feet of surface area.

   For small balls you can start with cubes and (I've only read about this, never actually tried it) place them on an upside down belt sander that has an open frame to contain the cubes.  The cubes randomly tumble on the moving belt and turn into balls.  IIRC you can add a wedge to the end of the frame to prevent the cubes from lining up with each other (preventing them from tumbling randomly).

2. 
   joinerswork | Jan 19, 2004 09:58pm | #4

   Loren,

   Think of suspending your sphere blank between centers 36" apart, plus some extra for waste stubs you'll cut off later.  The router is mounted on a stout arm that pivots on a bolt below the sphere blank, halfway between the centers.  The arm holds the router suspended in line with the centers, 18" away from a line going center to center.  Round nose bit in the router.  The arm swings center to center, cutting an 18"radius "kerf"; rotate the sphere a little, then make another pass with the router, repeat...I'm tired of this already!! Depending on how closely you approach a spherical shape in your initial glue up, it could take several trips around the world to mill the high spots off and get to your finished dimension. Like another poster pointed out, there's a lot of surface area on a sphere, then you get to sand it.

   Best wishes,

   Ray 

2. 
   UncleDunc | Jan 19, 2004 11:18pm | #5

   Here's a picture of a ball turning tool on a metal lathe. If you swivel it 90 degrees left or right, then you can mount the ball between centers, with the tool addressing the side of the ball. If you replace the single point cutting tool with a router, then you don't need to turn the ball at high RPM, and you can replace the lathe with any rough and ready arrangement that will hold two spindles on the same axis and allow you to turn the ball by hand.

   http://www.nucleus.com/~harlan/ball3.jpg

   Using a router also means you don't need as much rigidity as the U shaped frame provides. If you do a Google image search for "ball turning" you'll see the picture I wanted to post, from http://www.toolpost.co.uk Same principle but much simpler.

1. 
   Sphere | Jan 20, 2004 03:55am | #6

   line the inside of your dryer with sandpaper..chuck in the wood and turn it on for a week..you'll have a sphere..

   I thought I heard my name..

   Edited 1/19/2004 8:01:38 PM ET by SPHERE