I decided that I needed a Longworth Chuck so I decided I'd document the process for those who might want to make one.
First I started out with two pices of Flat playwood one 3/4" and the other is 1/2" thick. I cut them into 10" squares
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After finding the center on each one I made 3 circles. the first one is the diameter of the face plate that I intended to use to mount it to the lathe. In this care it's 2 inch diameter. The outer circle is 3/4" from the outside. The center circle is half the distance between the inner and outer circles.
Attachment 38431
Then I made them round using my bandsaw and circle jig.
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Next I drilled a center whole through both face plates and fastened them together using a 1/4-20 bolt and self locking nut.
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The next step is to cut 4 arc. The center of the arcs is the point where the center circle intersect the line the were used to find the center. The arc reached from the inner circle to the outer circle.
Attachment 38434