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Turning
an Open Segmented Bowl
This
article was reprinted with the permission of Kevin Neelley. For
more information about him and this technique you can visit his
website.
Open segment bowl construction is one of the several different
types of segmented bowl construction. The vase below is my first
try at open segmented construction. Since I first saw photos of
Bill Smith's incredible open segmented bowls on Yahoo's
Creative Woodturners Club, I wanted to give them a try. Particularly,
I wanted give one of Bill Smith's designs a try, so my first open
segment bowl is very similar to one his designs.
George Kattawar and Chuck Hale of Texas
Gadgets had just perfected their Open Segment Jig, one of which
they sent me for my appraisal. George has made quite a few open
segment bowls and used his expertise to fine tune the jig. I used
it in the construction of my vase. The jig comes with good setup
instructions, which is pretty easy anyway. George Kattawar includes
great open segment bowl design instructions and an MS Excel spreadsheet
for creating a segment cutting list. I used my miter
angle software for the vase's solid central ring but I used
George's software for the open segment portion.
Click on any photo for an enlargement.
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This is the completed open segment vase.
It has 495 pieces and took about a week total to assemble and
turn. The open segment rings are composed of 24 segments. The
closed segment rings were made 12-sided. I used Titebond II
wood glue. The outside was finished using Behlen's Jet Spray
lacquer.
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A top and inside view of the vase. It was
completely finished on the inside using a rag, moistened with
tung oil, on a stick.
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There are a number of different ring thickness' on this
vase: 3/8", 5/16", 1/4" and 1/8". I thought that
the vase would be much easier to assemble if the thickness of the
segments were accurately machined. I used my bandsaw to rough resaw
the lumber, then I used my thickness planer to finish the task.
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This is the frame-miter table saw sled I used to cut
all the segments for this bowl. The sled plans are found here.
Before making any saw cuts I made sure that my table saw blade was
perfectly vertical, which is very important. The open segments were
all cut at 5 degrees. The closed segments were all cut at 15 degrees.
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The open segments for this vase are extremely small,
some are less that 1/4" wide, which are difficult and maybe even
dangerous to clamp when cutting off. For cutting all of the open segments
I used a two-part stop board. The right-hand section of stop is clamped
into place after the segment cutting distance has been set. Then the
left-hand stop section is removed (see next photo).
Note that during a cut, there is a tendency for the saw blade to
push the segment board to the left, making a wavy cut. The segment
board can be clamped to prevent its movement during the cut. Gluing
a strip of fine sandpaper to the fence edge will help hold the segment
board in place if clamps are not used.
Always make sure there's no chips or sawdust between the segment
board and the stop board or fence.
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The left-hand stop section has been removed, creating
a gap between the segment board and the right-hand stop section.
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The segment has been cut off. Because the segment is
not against the stop, the wind from the blade blows the segment away
from the blade. If I did not use a two-part stop board, the cutoff
segment is so light that it would bounce around and probably bounce
into the spinning blade, damaging the cutoff segment and maybe throwing
it back into the operator.
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The base for the vase has been made and glued onto a
faceplate with waste block. When the vase is complete, I will part
off the vase from the waste block.
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I have installed the Open Segment Jig. The index wheel
was screwed onto my headstock threads and the faceplate was then screwed
on. The jig consists of two stands. The rear stand is used to set
the index wheel at the appropriate angle. The front stand provides
a platform and a stop for gluing on the segments at the correct diameter.
The spring plunger attached to the front stand is designed to hold
each segment tight for 10 to15 seconds while the glue sets up. I
found that the spring plunger wasn't very useful on my tiny segments,
so I didn't use it. It would probably work just fine on a bowl using
larger segments. Instead, I just held the segments in place using
the end of a mechanical pencil.
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The first row of open segments has been glued on.. After
letting it dry for about an hour, I lightly sanded flat the face of
the segment ring with the lathe off using a sanding block and 80-grit
sandpaper.. While I waited for the segment's glue to dry, I cut the
next row of segments.
It took longer to cut and sand the segments than to glue them onto
the faceplate. The jig worked really well..
I used a very light coat of Titebond II glue on each open segment.
The coat is so light that you can see through the glue coat and
almost no glue squeezes out between the segments. I got a bit overzealous
in gluing a few segments, so I used a pipe cleaner to remove the
excess glue. Titebond II glue dries clear and shiny so all visible
glue, as long as it wasn't a big gob, was invisible after I lacquered
the vase.
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The second row of open segments is being glued on. I
think I removed the spring plunger at this point to get it out of
the way.
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The third row of open segments is being glued on. Note
that the stop positions the segment at the correct diameter. Chuck
Hale has imbedded a ruler in the platform surface to make positioning
the stop very quick. I am holding the segment with my mechanical pencil
while the glue sets up.
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The fifth row of open segments is being glued on. The
design is starting to take form.
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The seventh row of open segments has been glued on.
Note how I'm using my sanding block to make sure that the top of the
ring is flat. Because I used my thickness planer on my segment boards,
there isn't much to sand. |
