Kevin's Woodturnings
  
DESIGNING A BASIC SEGMENTED BOWL USING A NO MATH METHOD

This webpage is intended for the beginning segmented bowl maker. This is basically a "no math" or "graphical" maybe a "very little math" approach to segmented bowl design. I have made three design sheets that will help the beginner through the design phase. Using these three design sheets, I have designed a 9-layered bowl using 12-sided frame-mitered rings. This webpage will walk you through the design steps.

To go to the webpage showing the bowl being constructed, click here. To go to the webpage that has plans for a frame-miter table saw sled that makes perfect ring segments, click here.

If you make a similar bowl and follow these steps, your bowl will turn out fine. Don't worry about the details of segmented bowl construction. Instead, spend your time thinking of an original design that you like. I'm sure that experienced segmented bowlmakers don't make bowls using all the steps on this webpage. I don't make segmented bowls this way either, but I think it's a good learning approach. Experience will tell you how to modify the steps. Until you are experienced, you shouldn't modify the steps until you understand how the changes will affect the segmented bowl construction. 

Click on any photo to enlarge it.

Fig0-1Bowl Design.gif (20083 bytes) Segmented Bowl Design Sheet

This first blank sheet is contains the instructions for using my three design sheets in designing a segmented bowl or vase. This sheet also has a grid for recording design measurements taken from the other two bowl design sheets. The filled-out grid will have all the dimensions necessary for cutting the segments in each of the ring layers. 

Fig1-1.gif (11428 bytes) Figure 1

This second blank sheet is used for drawing the outline of your bowl. This design sheet is big enough to design a bowl 12" diameter by 12 ring levels tall. Each row, 1 through 12, corresponds with a ring level of your bowl design. The grids on the sheet are intended to be 1" wide by 3/4" tall to make it easy to measure bowl ring dimensions directly from the sheet. But, I found that every printer seems to print the grids at different sizes. So, I suggest printing out one sheet then using a photocopy machine to enlarge the sheet to full 1" grid width.

Fig2-1.gif (10624 bytes) Figure 2

This third blank sheet is used for drawing one of the segments used in each ring level of your bowl. The dimensions taken off this sheet will be used to accurately cut the segment to size. You will need one of these sheets for each ring of your bowl because the segments are different sizes. This sheet is ONLY for 12-sided rings. The angle between the angled lines is 15 degrees, which is the setting angle for your table saw's miter gauge or sled fence. You will need to make a different angled sheet for rings with other than 12 sides. The horizontal and vertical lines on the sheet aren't drawn to any scale and are for reference only. Draw your segment full-size on this sheet.

Fig1-2.gif (13807 bytes) Step #1 (from Segmented Bowl Design sheet)

I have drawn the right-hand half outline of the new bowl on the Figure 1 sheet. This is the first step in the design process. If you want to see what the whole outline looks like, hold the left side of the sheet against a mirror so you can see the reflection of the sheet. The entire outline can then be viewed. This design has 9 rings. The bottom ring will be a solid disk. The other 8 rings will be segmented. I have decided to make the top, middle, and bottom rings from purpleheart and the rest of the rings from maple. The bowl will be made from 3/4" thick kiln-dried lumber, purchased from a local lumberyard.

Fig1-3.gif (20190 bytes) Step #2 (from Segmented Bowl Design sheet)

I have drawn the inner surface outline of the new bowl on the Figure 1 sheet using 1/2" wall thickness. The 1/2" wall thickness does not mean I'm going to turn the bowl to 1/2" thickness. The 1/2" is just a reasonably safe design thickness. You can turn your bowl thinner. On the other hand, if you don't make your segmented rings very accurately and they end up egg-shaped or the wrong diameter, then 1/2" might not be big enough. We'll take our chances on this one because I'm using a really accurate mitering sled (the one I designed on another webpage).

Fig1-4.gif (24239 bytes) Step #3 (from Segmented Bowl Design sheet)

I have drawn the inner and outer ring boundaries for each ring on the Figure 1 sheet. If we made our bowl from actual rings instead of segments, the ring boundaries would be the inner radius and outer radius of each ring. We need to transfer the inner and outer ring boundaries of each ring to Figure 2 sheet to find all of the segment cutting dimensions.

Fig2-2.gif (13851 bytes) Step #4 (from Segmented Bowl Design sheet)

As an example, I have decided to find the segment dimensions for ring #6. A compass is used to transfer the inner and outer ring boundaries of ring #6 onto the Figure 2 sheet, drawing an arc between the angled lines.

Fig2-3.gif (13483 bytes) Step #5 (from Segmented Bowl Design sheet)

The next step is to draw a horizontal line across the top of the outer boundary arc on Figure 2 sheet. This is the outer segment width line for the segments in ring #6. Then, draw a horizontal line across the point that the inner ring boundary arc crosses the angled lines. This is the inner segment width line for the segments in ring #6.

Note that the segment thickness is larger (and will always be larger) than the ring thickness. You might be able to ignore this thickness difference between segment and ring on small bowls, but on large bowls this could cause a wall thickness disaster. I designed the bowl for 1/2" wall thickness, but if I would mistakenly cut the segments to ring thickness, then I might end up with a bowl having 3/8" wall thickness, which could be chancy if the segmented ring is not perfectly round or exactly the right diameter.

Fig2-4.gif (13230 bytes) Step #6 (from Segmented Bowl Design sheet)

I measured the distance between the outer and inner segment width lines for the ring #6 segment. The distance was recorded in the "Measured Board Width" column of the Segmented Bowl Design sheet. This distance is the width of the board that the segments will be cut from.

Here's some food for thought. The board can be wider than this, i.e., the segments for most of your rings could all be cut from the same 1" x 2" nominal width board. Using the bowl design method introduced on this webpage, using wider boards would mean the excess segment wood would have to be removed from the interior of the bowl. This is not a problem with an open bowl but would be more difficult on a tall bowl, like the one designed here.

Fig2-5.gif (13230 bytes) Step #7 (from Segmented Bowl Design sheet)

I measured the length of the inner and outer segment width lines for the ring #6 segments on Figure 2. I recorded the lengths in the "Inner Segment Width" and "Outer Segment Width" columns of the Segmented Bowl Design sheet.

The inner segment width measurement is only used for calculating the board length. So, if you are using nominal width boards and not cutting your boards to width, then you do not need to measure and record the "Inner Segment Width" measurement. Also, you will not need (or be able to) calculate board length.

Fig0-2BowlDesign.gif (26982 bytes) Step #8 (from Segmented Bowl Design sheet)

I calculated the board length for cutting ring #6 segments using the formula from the Segmented Bowl Design sheet. The distance is recorded in the "Board Length" column of the Segmented Bowl Design sheet. 12 segments can be cut from a board of this length, although I always add an inch or so extra to the cut board length.

On this example sheet, I have shown all the cutting dimensions for all the rings in the new bowl.

   

Now I have all the dimensions necessary to cut the segments for all the rings for this bowl.  I'll use the dimensions to cut the boards to length and width, and then cut segments from the boards.

Using the Segmented Bowl Design sheet, it looks like I need about 40" of 1"x6" kiln dried maple and about 14" of 1"x4" purpleheart to make this bowl.

The next thing to do is to start cutting segments and constructing the bowl. You can get started by viewing my "Making a Basic Segmented Bowl Using a No Math Method" webpage (click here).

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