Bowl scooper

[Bombarde16]

 

Here's my take on the bowl scooping jig from David Marks's sculpted bowl table.  Mr. Marks used a router whereas I did mine with a circular saw.  The overall concept, however, is the same.  The tool is mounted on a circle sized to spin nicely within a circular opening.  By plunging the saw a smidge at a time, you can rotate through 360 degrees.  (Hey look, a circular saw going in a circle!)  Plunge a smidge more, spin...Plunge a smidge more, spin...

 

I used a circular saw first and foremost because it's a simpler jig to build.  Simply tack some scraps onto the base and clamp whereas the router needs to be cradled within a set of curved rails.  Moreover, the circular saw can cut a wider variety of shapes:  Mr. Marks admitted during the show that the precise dimensions of his router rails were arrived at "by trial and error...a lot of trial and error."  That said, his jig cuts bowls that have a fixed relationship between depth and width.  i.e. If you arrive at your target depth and the bowl isn't wide enough, you have to cut deeper (potentially breaking through) in order to get a wider bowl.

 

The circular saw can be scooted and clamped forward or backwards on the base, meaning that you can cut down to your target depth and then widen the bowl as desired without going deeper.  The resulting bowl isn't a perfect spherical cap, but it's close enough to fool the eye.

 

This was a quickie build and it did a decent enough job for a prototype.  For future iterations, I'd make a few changes:

• The base circle should be larger to allow for cutting wider bowls.
• I should have spent more time getting the fit between the base circle and the circular opening better.
• The saw is cutting through its own kerf.  A larger channel (say, from a 1/4" router bit) would allow sawdust to escape.
• Better materials.  The circular base is an old scrap of MDF that I used to test a painting schedule for my daughter's bedroom.  The circular opening is a ratty piece of exterior plywood that spend a year outdoors.

[Dave H]

Particleboard demonstrated a jig for doing this very thing on the forum once. I like your ingenuity, what if you cut the guide circle bigger after the initial scarfing out of the bowl shape, than add a scrap to the front of the circle that holds the circ saw, the scrap tightens it inside the bigger circle. This would make a more exact extended circle (I'm just spit balling I sure whatever you do will turn out perfect) I like this jig I will mentally file this idea away. You should send it into one of the woodworking magazines they have a helpful tips section sometimes they have some pretty nice prizes.

[Dave H]

Don did something similar to this but, it seems to me he had an overhead pin and a pivot hole

http://www.youtube.com/watch?feature=player_detailpage&v=LVlW73do-qo but this was  effectively what he achieved.

[duckkisser]

I would have use a lathe   a very very large lathe similar to this http://www.youtube.com/watch?v=2EysRz5FiKg