Segmented Bowl

or turners who have never tried segmented turning or for those F who would like a refresher on Turning Your First the basic concepts, here is a simple, easy approach to turning a segmented bowl. This quick, accurate method will acquaint you with the fundamentals SEGMENTED BOWL of segmenting, which you can then Jim Rodgers apply to more complex pieces. The bowl presented here makes use of a solid layer of wood for the foot and four progressively larger rings, each one comprising multiple segments cut at predetermined angles.

Segment-cutting sled As you would imagine, segmented projects require careful attention to creating a blank prior to turning. The table saw is my preferred tool for cutting segments, and a sled with a fence set at the correct angle is the best way to produce identical segments. Some time invested up front creating a good sled will help you far into the future. I recommend making and using a Wedgie Selecting wood Make a drawing Sled, a simple fixture designed by You will need to determine which Make a full-sized drawing of your renowned segmented turner Jerry wood species to use; I had some very bowl on graph paper with your Bennett. Plans and instructions for dry Eucalyptus cut a few years ago desired profile. This drawing will help building this sled, as well as helpful from a friend’s yard. Mill the wood you determine the ring diameters and videos, can be found at Jerry’s to the desired thickness you want thicknesses as well as the segment website, segeasy.com. Regardless of for each level, or ring. I chose ⅝" sizes required. Allowing for extra wall the sled design you choose, the goal (16mm) thickness. It is important thickness now will help you mini- is to be able to cut desired angles that you select wood that is thor- mize any problems you might have accurately and with repeatability. oughly dry, with moisture content later in aligning the rings or turning of six to twelve percent. Using the bowl. Next add horizontal lines to green, or unseasoned, wood intro- indicate the foot and ring thicknesses, JOURNAL ARCHIVE duces a greater likelihood of wood based on the thickness of the wood movement, which will cause you will be using. Add a centerline to CONNECTION Part 1: Cut Accurate Segments Jim Rodgers has written glue joints to fail. the drawing and number each level, previously in American or ring, of the bowl from the base Woodturner on segmenting. Plan your bowl upward (Figure 1). His 2005 article on cutting Unlike other kinds of wood- Note that drawings made with Segmented accurate segments (vol Turning turning, segmented projects sophisticated software or using 20, no 4, page 24) offers School require detailed planning of trigonometry functions will render

By Jim Rodgers helpful information, 24 the piece you wish to create. For American Woodturner Winter 2005 more accurate results, as a simple including an alternate this project, I decided on a small two-dimensional drawing cannot sled design and tips on gluing segments into popcorn bowl that would fit in account for the three-dimensional rings. AAW members can access all past your lap—about 3" (8cm) tall by 7" journal articles online at woodturner.org. aspect of the bowl’s curvature. This is (18cm) diameter. why allowing for extra wall thickness

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Plan your segmented bowl

Outside Radius Inside Radius

Figure 1. Start with a full-sized drawing of your desired profile, Figure 2. Measure the required width of each segment by subtracting then indicate the thickness of each segment layer, or ring, with the shortest inside radius from the longest outside radius. Note that horizontal lines. the foot layer is a solid circle of wood, not a segmented ring.

is especially important when using a ring’s circumference by twelve to get the resulting number as the width of two-dimensional drawing. the length of each segment’s long, or each strip (Figure 2). outermost edge. Determine board length Cut your stock Planning your bowl requires a few Determine segment width With all of the critical calculations simple calculations based on your You will also need to know the made and recorded, you will have a initial drawing. As you make the calcu- width of the wood strips that will cut list you can use to begin prepar- lations, record the results in a table for make up each segment. To make ing the wood, first by ripping the easy reference. First, you will need to this determination, go back to your timber to the needed width, then determine the board length needed to drawing and measure both the by cross-cutting the strips to overall cut the right number of segments for longest outside and shortest inside length. Label the strips as you rip each ring. The board length is equal to radii of each ring, using the centerline them so you can easily see which the circumference of each ring (plus as the point from which to measure. rings they are to be used for. about 4", or 10cm, for safe holding Subtract the inside measurement from Set up the table saw to cut the individ- during cutting). To find the circumfer- the outside measurement and record ual segments to the correct length ence of each ring, measure its diameter (d) on your full-sized drawing and multiply that number by 3.14 (Pi, or Cut the segments π)—since the circumference of any circle = π × d.

Determine segment length In order to cross-cut the individual segments on your sled, you will need to determine the length of each segment’s longest, or outside edge. This is found by dividing the ring’s 1 2 circumference by the number of seg- Use a 30/60/90 triangle to set the fences on Cut the individual segments. The length of ments in that ring. In my example your table saw sled to the desired angle. all segments is made identical with the use of project, each ring is made up of an adjustable stop (bottom right of photo). twelve segments, so I divided each

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18_SegmentedBowl.indd 19 9/9/15 2:04 PM Glue the segments True it to glue it Use a waste block attached to a faceplate as the A flat board with 80-grit abrasive resting on base on which to assemble your segment rings. the toolrest for support works well for flatten- A straightedge held across the face will help ing each ring prior to gluing on the next ring. you determine its flatness, which is critical to a Keep the lathe speed low, about 600 rpm, good glue joint (Photo a). during this process (Photo b).

3 Glue the segments into rings, using a band clamp to apply even pressure. a b

and at the correct angle. My setup by pivoting its two fences. The angle between the two fences. Move the fences includes a zero-clearance throat plate, a between those fences is set to the neces- until they touch the edges of the triangle, good quality finish-cut saw blade, and a sary included angle for the segments; then tighten down the fences (Photo 1). stop for cutting multiple segments at the the first half of a segment is cut using Cut all the segments for each ring, same length. You also need to set your one fence and the second half, using keeping the top surface of each strip (marked table saw sled to cut the segments at the the other fence. When you cut the seg- with a pencil line) facing up (Photo 2). I find desired angle. The included angle is deter- ments, there is no flipping the strip, as it helpful to organize the rings in labeled mined by dividing 360° (a full circle) by you would have to do with single-fence plastic bags to avoid confusion over which the number of segments. So, for example, sleds. To realign the segments with the segments are for which rings. Carefully sand any twelve-segment ring, regardless of its greatest precision during glue-up, mark each segment to clean up any frayed edges, circumference, will require 30° angles on the top face of each wood strip with a being careful not to round over corners or each individual segment. continuous line prior to cutting and also touch the face of the cut edge. Cutting segments using the Wedgie mark one edge. An easy way to set the Sled is a little different from cutting on fences for a 30° cut is to use a commonly Glue segments into rings an average table saw sled: the Wedgie available 30/60/90 triangle. Place the Dry-fit the segments of each ring can be adjusted to cut different angles triangle on the sled with the 30° angle together, keeping the top surface pencil

Simple centering methods

Faceplate

Glueblock

Foot layer First ring 4 5 6 Three methods of centering a ring when gluing it to the previous layer. Use a ruler or your fingers as a gauge, or mount the ring in large chuck jaws mounted on your tailstock.

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lines facing up and the edge lines alter- (Photos 4, 5), be sure to true the ring’s nating, with one facing inward, the diameter on the lathe before adding next outward, etc. A rubber band will the next ring to minimize “creeping Turn and finish hold the segments together while you errors” of subsequent rings. On-the- check the quality of the glue joints; lathe methods can provide more shine a light from behind the ring—no centering accuracy. If you own a light shining through indicates good tailstock live center system that has joints. When you are satisfied with the headstock threads, you can mount a fit, apply glue to the edges and use a scroll chuck with large jaws on your band clamp to apply pressure (Photo 3). tailstock (Photo 6). This will center Do this for each ring. the rings very accurately for gluing, If gaps appear during your dry fit, it and you can use the tailstock crank is possible you have allowed the strips to apply gluing pressure. to slip while cross-cutting the seg- After the glue is dry on your first ments, or frayed edges or stray sawdust ring, true up the exposed face before may remain. It may be necessary to adding the next. An easy way to do 7 clean up the edges further or recut the this is to sand the surface on the lathe A completed bowl blank built from four segment rings and a solid layer segments for that ring more carefully. using a flat board with abrasive glued for the bowl’s foot. to it (See Sidebar). Continue this process Make a bowl blank until all of your segmented rings are When all of your segment rings are glued on and you have a rough seg- glued up, the next step is to glue them mented bowl blank (Photo 7). together to make a bowl blank, start- ing with the solid foot layer on the Turn your bowl bottom, then adding the rings from Shape the exterior of your bowl first by smallest to largest as you go toward the following the drawing and ignoring the rim of the bowl. I recommend assem- “steps” between the rings. If you follow bling your bowl blank on a glueblock the shape, the steps will disappear as the attached to a faceplate. Flatten the shape is achieved. Keep the base over- glueblock, verifying its flatness with a sized for extra support until the last steps straightedge before adding the bowl’s (Photo 8). Next, work the interior from foot. Glue on the solid layer that will the rim downward one or two rings at become the foot. Now build your bowl a time. After completing the interior, blank one ring at a time. reduce the base to proper dimension As you glue on each successive ring, and cut a clearance groove at the bottom 8 The outside profile turned. Leave the rotate it by half a segment’s width of the defined foot to allow access for foot material thick for added stability to alternate the vertical glue lines sanding the bowl’s foot (Photo 9). during turning near the rim. and create a “brick-laid” pattern for I prefer to sand and finish both the strength. You may want to mark the interior and exterior while the bowl is center of one segment with a pencil still mounted on the lathe for ease of line to ensure the next ring aligns at handling. When you are satisfied with the halfway mark accurately. your finish, part off or cut the bowl Flatten one side of each ring on a from the glueblock. Sand and finish sanding disc or flat sheet of 80-grit the bottom of the foot by hand. abrasive. After flattening the foot, glue the smallest ring onto it, taking care to center the ring the best you Jim Rodgers is president of the Segmented can. Centering each ring can be Woodturners, a virtual AAW chapter (segmentedwoodturners.org). He also offers 9 done in several ways. If you do it off information on the basics of segmented Sand your segmented bowl, apply the lathe with a ruler or by gauging turning at his own website, jlrodgers.com, finish, and part or cut it off the lathe. centeredness with your thumbs and can be reached at [email protected].

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