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A Bowl From A Board

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From: book: The Art of Segmented Turning

Page 1 of 1

You might be thinking that segmented turning uses a lot less wood compared to conventional turning because there is very little hollowing involved. You would be wrong. In conventional segmented ring construction, many board feet of good wood goes into the trash. Many years ago at an AAW symposium, Mike Shuler, a well- known woodturner from Santa Cruz, California, demonstrated making a bowl with very little waste. He had advanced a technique based on construction methods used in the salad bowl industry. Shuler also credits Dale Nish, in his classic book Creative Woodturning, for describing the technique of stacking angled rings band-sawn from boards to create a bowl shape. This is a great example of how sharing ideas leads to innovation and the whole field of woodturning advances one more step. That is not to say that we should all copy each other’s ideas, there is a big difference between plagiarism and what Shuler describes as, "spring-boarding from an existing concept." With Mike Shuler’s encouragement, I will describe the basics of this ingenious technique. I offer it so you can use the basic technique and possibly take another step in a new direction.

Instead of cutting, gluing, and stacking individual rings, I will glue together two large half-rings and then band-saw angled rings that will be stacked into a bowl shape. I chose a board of straight-grained purpleheart about 5-1/2 inches wide by 30 inches long. Using my miter saw, I cut 40 segments with a 4.5° angle on each side (8o times 4.5° equals 360°). I cut the pointed ends of the segments less than 1/4 inch wide. Before cutting the segments, I laminated pieces of maple veneer and thin ebony together in order to create 20 splines that I will glue between every other segment. For the other 20 seams, I cut the same size spline from solid holly. These unglued segments and splines are shown in photo 11-42.

Sanding segments of this size presents a challenge because of the length of the glue lines and the short length of the wood grain. Just a little bit of sanding heat will warp the surface. Actually, just releasing wood tension by cutting such short, wide segments can result in some warping. It is certainly tempting to glue without sanding, but I know I can improve the glue lines, so I sand. First, I changed the paper on my disc sander. Sharp, fresh sandpaper will reduce time on the disc and therefore reduce heat build-up. A dry-fit of the segments confirmed that my cuts were right on and that very little sanding would be necessary. I decided to freehand-sand half of the seams and then glue those 20 pairs together with a laminated spline in between (photo 11 -43). To minimize warping, I sanded the segments in stages, just a little sanding followed by cooling time while I sanded the next. After a couple of very light sandings, the joints were ready for glue. I performed the bright light check on each seam and waited for any sanding heat to dissipate before gluing each of the 20 pairs. Never attempt to glue warm segments, the glue will set too quickly and you won’t have enough alignment time. Perfect glue joints are vital, one bad joint and the whole project is a loss. Unlike other ring-construction where there is an opportunity to replace a bad ring, with this technique replacing a single defective ring is not an option.

This article by Malcolm Tibbetts is excerpted from The Art of Segmented Woodturning.

I continued to assemble the large ring by joining pairs to form groups of four and then groups of eight, with two groups of four left alone. The sections of eight required a gluing caul to apply perpendicular clamping pressure. I attached triangular pieces of MDF with a bead of hot-melt glue, as shown in photo 11-44. With smaller segments rubber bands provide adequate clamping pressure, but with segments this large, I chose small bar clamps. In photo 11-44, I am gluing the center seam, the other seams were previously glued. Before each gluing stage I performed a dry-fit and made minor disc sanding adjustments to ensure that the ring stayed round. It is critical that the final ring shape be perfectly round, not oval. If any minor adjustments are necessary I want to spread them across many seams, I do not want to make a major adjustment near the end of the construction..

Each half-ring now consisted of two sections of eight and one section of four. Another dry-fit followed by a few minor disc sanding adjustments resulted in two matching halves. To glue these (photo 11-45), I used the half-ring method as described in Chapter 7. I only had to deal with three sections and two splines per side, which made the job relatively easy. After this step, unlike conventional segment ring building, I did not join the two halves into a solid ring. I smoothed the surfaces using the disc sander and drum sander, placed the last holly splines in between the halves, and dry- clamped them together with a hose clamp..

This article by Malcolm Tibbetts is excerpted from The Art of Segmented Woodturning.
To create a bowl shape from this large flat ring required cutting angled rings whose top and bottom diameters matched the diameters of adjacent rings. There are choices: how narrow and at what angle should the rings be cut? Narrow cuts will result in more rings and a taller bowl, but if the rings are too narrow the walls may be too thin, resulting in disaster. The size and shape of the angled rings will determine and limit your bowl shape options. Using the actual dimensions of my ring, I have drawn the layout I used for this bowl in photo 11-46. To be on the safe side, I allowed almost 1/8 inch for saw-kerf loss. To achieve a slight curve I drew the rings a little wider, with a slightly steeper angle than necessary toward the inside (the bottom of the bowl). This layout resulted in less height because fewer rings could be cut — not a big deal, the bowl is tall enough. If your goal is maximum vessel height with minimum waste, then you must lay out cuts that are steeper and closer together. In any layout, make sure your diameters line up to provide you with adequate wall thickness. It’s tempting to cut very thin rings and thus create a taller vessel, but for me the risk is not worth the extra height. In addition, if you cut very thin rings you eliminate room for error and you limit the bowl profile to almost a straight line. Straight lines are not necessarily bad, but I wanted a slight curve.

After deciding on my layout I used a compass to draw concentric circles on the two half-rings that were still clamped together. I separated the two halves and, using a 1/2-inch fine-toothed blade, proceeded to band-saw the cuts. As I made successive cuts, I adjusted the blade angle to achieve the results as drawn. In photo 11-47, I am carefully making a cut; a lack of focus here and the whole project is lost. The half-rings are shown in photo 11-48.

The remainder of the project was straightforward. I glued the half-rings together with a small piece of holly in between, built ebony and holly rings for the top and bottom, stacked the layers together one at a time, and turned the bowl shape, titled BLACKBERRY SWIRL, that you can see in photo 11-49.

The technique of using band-sawn angled rings has been around for many years, but as far as I know, with the exception of Mike Shuler, whose turnings are much more complex than this example, few turners have experimented with it or tried to take it to a new level. As I write these words, images of combining other lamination tricks in combination with this technique enter my head. I hope your own brain is spinning with ideas.

This article by Malcolm Tibbetts is excerpted from The Art of Segmented Woodturning ©2005 Linden Publishing .