Kevin's Woodturnings
  
OPEN SEGMENT BOWL CONSTRUCTION

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 TexasGadgets.com had just perfected their Open Segment Jig but now they appear to be out of business.  George has made quite a few open segment bowls and used his expertise to fine tune the Jig.  I used the Jig 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 lathe. 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 thicknesses 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 segments were accurately thicknessed.   I used my bandsaw to rough resaw the lumber, then I used my thickness planer to finish thickness.  

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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 on another page on this website (click 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 zinging 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 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 drying 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 really worked.

I use a very light coat of Titebond II glue on each open segment.  You can see through the glue coat.  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 opne segments is being glued on.  Note 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 while the glue sets up using my mechanical pencil.  

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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 thickness sanded my segment boards, there isn't much to sand.   

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The eighth row of open segments and the central ring has been glued on.  I have removed the Open Segment Jig.  I want to lathe the inside of the vase now, while I don't have very far to reach inside.  Since I'm unsure how strong the vase is, I decided to lathe smooth the central ring and install my steady rest so there will be little stress on the vase when I lathe the inside.  To lathe the outside of the central ring I used a very sharp skew as a scraper.  Skews used like this, on the outside of segmented bowls, are very good because the grain direction is all the same and they leave a very fine surface finish.

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I have installed my steady rest and the vase inside is ready for lathing.

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I used my Sorby RS2000 with a sharp teardrop-shaped scraper to cut the inside of the vase.

 

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The vase inside has been lathed smooth.

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The tenth row of open segments has been glued on.

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The twelfth row of open segments is being glued on

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The final row of open segments has been glued on.

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I have remove the Open Segment Jig, including the indexing ring, and installed the vase's lip section.

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The steady rest was reinstalled the for the remainder of the vase lathing.  The next part to lathe is the remaining vase interior.

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I used a small Sorby crookneck scraping tool with a sharp teardrop scraper to cut the interior.  This tool is really only adequate for cutting a few inches beyond the tool rest, but that's all I have to do.  It does a nice job with no sanding necessary.

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With the inside of vase complete, I used a sharp skew, held horizontally like a scraper, to cut the outside of the vase.  Since the skew is cutting thin shavings there is no problem with shavings going under the steady rest rollers.  

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A small skew and small spindle gouge were used to shape the vase's lip and base.  

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This small screwdriver and an even smaller one was used remove the remove the shavings from between the open segments.  Compressed air did a pretty good job of getting out most of the shavings.

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The vase was sanded up to 320-grit sandpaper followed with a sanding using a maroon scotch brite pad.  Scotch brite is color-coded for abrasiveness.  I think maroon is "medium".

The next step was to part the vase off the faceplate.  I used the above Sorby parting tool.

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I parted the base until I had a 1/2" ligament, which is shown in the photograph.  With the lathe off, I hand sawed through the ligament.  Then, I reverse turned the remaining stub off the vase base.

 

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