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Mark chats with George Geissler before the demo.
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Mark highlights the grain on this block of wood and discusses the importance of cutting down hill.
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This jig is used to help students understand the concept of cutting down hill.
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Mark holds the two halves which will become the sphere.
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The first half is held in a Stronghold chuck.
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The surface is made flat.
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The diameter of the piece is measured using an electronic caliper.
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Mark used a diagram to show how the finished half should look.
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MARK KRICK DEMONSTRATION DECEMBER 2001
by Lee Buck
Mark Krick demonstrated
his method for turning perfect hollow spheres with an internal center stem. Mark has been making these
spheres as the basis for his carved sculptural pieces. The technique is also used for his bagel boxes.
Mark suggested a session should begin with waxing the lathe bed, and filing and dressing the tool rest.
He then used a glued up cherry piece to demonstrate the concept of cutting uphill and downhill. To
turn downhill a bowl should be turned from large diameter to small on the inside and from small diameter
to large on the outside.
The demonstration piece was a mahogany sphere turned bowl orientation.
Mark bandsaws a blank, mounts it between centers and makes a partial parting tool cut at the center
then continues the cut with a bandsaw. He mounts one half in a chuck, trues the piece, then measures
the diameter with a digital caliper. Using a compass he draws a circle on a whiteboard the same diameter
as the piece and draws another circle inside the outer circle to represent the wall thickness. Draw
a diameter, and from both points where the line intersects the circle, use the compass, still set at
the diameter, to strike intersecting arcs. A line drawn from the point of intersection of the arcs to
the center point of the circle will be at a right angle to the first diameter. Draw a straw along
a diameter to the center (where the diameters intersect) the thickness desired for the center stem.
Draw a circle at the center representing the thickness of the stem and drill a small hole through the
center. Hollow the cylinder between the outer wall and the circle representing the stem. Marks
uses a paper pattern derived from his drawing to gauge the wall thickness. Clean up the inside.
Mount the other half and turn to exactly the same diameter as the other piece. Repeat the
process from the first piece. Remove from the chuck and sand the edges of each piece on a flat surface.
Apply glue and use the drill bit as a locating pin through the center hole and glue the pieces together.
Mount the piece between centers using a cup center and true the cylinder. Mark the
center and measure the diameter precisely. Mark end points of the cylinder using the diameter measurement.
Face off the ends to the mark. Calculate the length of the sides of an octagon of that diameter.
Mark uses a computer program and provided print outs of the lengths for various diameters. Set calipers
to the calculated distance and mark at the center, 1/2 the length on either side of center line. Mark
the ends to the octagon length, 1/2 on either side of center. Mark used these lines as a guide to turn
a sphere. Unfortunately there was something wrong with the calculations and frankly the writer didn't
catch or understand the correction. We hope George will explain it when he is up to it. The point
is to create a line half way between the centerline and the end and another between that line and the
end and turn away between the lines at about 45 degreed.
Hold something ring shaped against the piece
to locate high or low spots and carefully improve the shape. Turn the piece 90 degrees and remove the
stubs.
At this point Mark carves his freeform designs.
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