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Step 11Modify sphere-cutting jig for base
The base of the chair is built similar to the body, but smaller, solid and has a concave surface the same radius of the chair. The chair sits in this concave well.
When sitting in the chair I wanted to be able to have my feet touching the ground. Any higher and your legs would dangle and pressure would be on the backs of your knees. I found a seat height of 16 inches worked well. With a 4 inch cushion and a 4 inch thick chair body this meant the concave surface had to start at 8 inches.
The concave surface is cut with a swinging cutter bar similar to the one for the half-sphere, but mounts to a swivel above the stock. The concave section needs to have the same radius as the outer surface of the half-sphere. The inner cutter used for the first section is 20 inches so it can't be reused for the base. The concave cutting arm for the base needs to be 24 inches.
The swivel point for the arm needs to be 32 inches above the turntable (24 + 8) and precisely centered. The best tool for this is a plumb bob. The wood arms holding the crossbar are 36 inch pieces of 2 x 4 with some simple bracing. Find the center of the crossbar member and drill a small hole to pass the plumb bob string through. Reposition the vertical 2 x 4s until the plumb bob aligns perfectly on the center of the turntable. This is easiest to setup when no stock is on the turntable and the center point clearly visible.
Redrill this hole for the swivel when the jig is setup and secured.
When sitting in the chair I wanted to be able to have my feet touching the ground. Any higher and your legs would dangle and pressure would be on the backs of your knees. I found a seat height of 16 inches worked well. With a 4 inch cushion and a 4 inch thick chair body this meant the concave surface had to start at 8 inches.
The concave surface is cut with a swinging cutter bar similar to the one for the half-sphere, but mounts to a swivel above the stock. The concave section needs to have the same radius as the outer surface of the half-sphere. The inner cutter used for the first section is 20 inches so it can't be reused for the base. The concave cutting arm for the base needs to be 24 inches.
The swivel point for the arm needs to be 32 inches above the turntable (24 + 8) and precisely centered. The best tool for this is a plumb bob. The wood arms holding the crossbar are 36 inch pieces of 2 x 4 with some simple bracing. Find the center of the crossbar member and drill a small hole to pass the plumb bob string through. Reposition the vertical 2 x 4s until the plumb bob aligns perfectly on the center of the turntable. This is easiest to setup when no stock is on the turntable and the center point clearly visible.
Redrill this hole for the swivel when the jig is setup and secured.
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