SEGMENTED TURNING

What is it? Segmented turning is the creation of a bowl, vase or similar object by the assembly of small wooden segments. The segments are assembled into rings and the number of segments required for a ring will determine the angle of each of the segments. A number rings are assembled on top of each other to create the bowl or vase. This computer software described in this document facilitates the calculation of the segment length of each ring.

Terminology? Before more detail is given on creating a design and performing the calculations certain terms must be defined to provide the necessary language.

The Segment:

The segment is fully defined by four properties. The width defines how broad the segment is and is also the width of the strip of timber the segment is cut from. The thickness defines the height or how thick the segment is. The length of the segment determines how many segments make up a ring. Knowing the length, which we calculate by using some basic trigonometry and the angle, the segment is fully determined. The angle indicated in the figure above is often referred as the mitre angle or the cutting angle. This angle is half the actual wedge angle of which the segment is part of. See figure below. To determine the length of the segment you must first establish the number of segments you wish for a ring. For example, for a 12 segment ring the wedge angle will be 360 divided by 12 or 30 degrees. The mitre angle is half the wedge angle and is therefore 15 degrees. By trigonometry, the length is; 2 x radius x TAN(mitre angle) By applying this simple formula to every ring in the object we wish to build we obtain all the necessary segment lengths. The computer software described in the following pages does all the calculation of lengths and prints a clear table of values for all rings in a project.

Read on…

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The Project: Plan Drawing - A Bowl Before attempting a project it is necessary to draw a plan. 2mm graph paper is a good choice. Draw the profile or shape of the bowl or vase you wish to make. Draw only the right hand side making the left side of the graph paper correspond to the centre of the object. See the plan below for a simple bowl containing twelve rings and three types of timbers, cypress, meranti and redgum. Begin by drawing the base. The base for this bowl will be 160 mm in diameter and have a thickness of 30mm. Number the rings 1 to 12 from the bottom to the top. Draw the bowl’s shape making the thickness of each ring 10mm, except for rings 5 and 9, which will have a thickness of 3mm. In addition, you need to determine the number of segments for each ring. For our sample bowl below we will have each ring made from the same number of segments. We will choose 12 segments, making the mitre angle of the segment 15 degrees (180/12). For each ring, draw the thickness of the ring and width of timber required as a rectangle around the outline of the bowl. Allow 5mm excess on the inside and outside of the bowl. Also measure the radius of each ring from the plan (the distance from the centre to the outer edge of the ring). See plan drawing below.

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We are now ready to use the Segmented Turning Helper software to enter the necessary data from our plan and use the software to calculate the segment length for each ring. Given the input data, timber, number of rings, mitre angle, thickness, width and radius, obtained from the plan drawing, the Segmented Turning Helper software will calculate the length of the segments for each ring. In addition the software will calculate the vernier length, stock length for each ring and a complete stock list. The software will also provide a 2 dimensional sketch of the object and also render a 3 dimensional image of the object. The 3D image can be rotated and zoomed to see high level of detail. A related image of the project may also be specified and printed with the data table. See the following documentation for a full description on how to use the software.

Using the Segmented Turning Helper Assuming the software has been installed on your computer and ready to run, double click the Segmented Turning Helper icon on your computer desktop. The program will open and appear as shown below.

Click the New Project icon to initialize a new project. In the New Project box enter the number of rings in your project and the diameter and thickness of the base. Also, enter the timber name for the base. The filename is initially set to ‘Untitled’. You can change it to a more meaningful name but if you don’t you can assign a better project name later when you save your project or exit Segmented Turning Helper. Click the OK button to create a new project with the designated number of rings and specified base. Note the base is not considered a ring as it is prepared from solid timber. The screen is refreshed to display an empty data table containing a set of rows equal to the number of rings in the project. The information for the base is shown below the table. The computer screen should now look something like the figure below.

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For each ring, enter the timber and number of segments. The mitre angle is automatically calculated by the software as you enter the number of segments. Now enter the segment thickness, width and radius values for each ring. All dimensions are in millimeters. These values are all obtained from the plan drawing. The computer screen should now be similar to the image below and the software has all the data required for calculating the segment lengths.

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Click the Calculate button to calculate the segment lengths. The last three columns in the table are filled by the calculations performed when you click the Calculation button. The table is updated as shown above in the peach colored columns on the right. The segment length column gives the length of the segments for each ring. The vernier length values are a little smaller than the segment length values and represent the perpendicular distance from the table saw blade to the stop block. The values in the Vernier Length column are used to measure the distance from the table saw blade to the stop to give the correct segment length. The stop I have contrived is a digital depth gauge easily adjusted to measure the vernier length. See the section ‘Cutting Accurate Segments’ for clarification of the vernier length.

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Project Drawing

2D Drawing

Once all the project data has been entered, the project drawing can be displayed by clicking the Draw button in the Project Drawing box. You can scale the drawing to fit the screen by changing the scale value. If the displayed drawing is too large enter a value less than 2 and click the Draw button again. If the drawing is too small increase the scale value. Check the Black Pen check box to draw the project with a black pen otherwise wood colors will be used.

The Draw Ring # (Ring Number) check box, if checked, will attach a ring number adjacent to every ring. See the diagram below.

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3D Model

Clicking the 3D Model button will render the project in 3D and you can observe the object you wish to construct in full 3D splendor. The various radio buttons provides a different rendering method. Below are three examples.

Example 1 Wireframe Model

The wireframe model provides a detailed line drawing of all rings and segments and may sometimes, depending on the object, appear very complicated as the rings overlap.

Example 2 Simple Model This model renders the object with a single color and draws the segment edges with a black pen. The base is dawn with a different color.

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Example 3 Wood Texture Model

The Wood Texture model will try to render the object with natural wood textures or colors corresponding to the timbers specified in each ring of the data table. Of course, there are hundreds of timbers available to wood turners and not all timbers are recognized by the software. Only a small set of timbers are internally defined in the software. These are listed in the adjacent table. If the designated timber in a ring is not recognized the Cypress timber texture/color will be used.

User Defined Wood Textures If you use timbers not in the supplied set you can still render your object with realistic wood textures/colors by supplying your own small image of the required texture. The image you supply should be approximately 100 pixels wide and 100 pixels high and should be saved to the Textures folder, generally; C:\Program Files (x86)\Segmented Turning Helper\Projects\Textures In fact, I have already supplied some textures for you. You will find these wood texture files in the Textures folder. The texture images are Cedar, CeleryTopPine, Fir, HuonPine, Mahogany, Teak and Wenge. The texture images can be either a .jpg (JPEG) or .png (PNG) image file.

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Printing Your Project Click the Print Preview button to print the table data, timber stock list and 2D diagram of the project. The output is sent to the screen and from there you can left click the printer icon to send the output to the printer. The figure below shows the full output of the project developed in the previous sections.

Page 1

Page 2

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Click the printer button at the top left of the screen to send the printout to the printer.

Note: You may be wondering where the photo of the project comes from? I have built the bowl project described above previously and have taken a photo of the completed bowl and saved the image to the computer. See the documentation (Select Project Image) below that describes how to include an image of your project, if you have one.

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MenuBar Commands

Icon Segmented Turning Helper icon.

New New Project. Click this icon to initialize a new project. This allows you to declare the number of rings required for your new project and the size and thickness of the solid base and set up a new project table for data entry.

Open Project Open existing project. Clicking this icon will open a Windows File Open dialog when you can find all your existing projects. Select the required file and click the open button.

Save Project Click this icon to save your project at any time. Saving your project for the first time requires you to supply a file name. Choose a good, descriptive file name which identifies the project as this will help find and identify your project later. You will be asked to save your project when you exit Segmented Turning Helper.

Calculate Segment Lengths After you have entered Timber, Number of Segments, Mitre Angle, Segment Thickness, Segment Width and Radius for each ring, click the Calculate button to calculate the segment lengths.

The initial data that is entered in the data table is obtained from your project plan drawing as described earlier in this document.

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Geometry Tools

This command exposes three useful utilities not directly associated with the calculation of segment lengths. Select the required tool by clicking the tab on the left.

Draw Grid This option will draw a grid to any required size. When planning a segmented turning project graph paper is required to draw the object to be constructed. The draw grid option will reproduce purchased graph paper. Below is an example of 10mm size grid with highlighted lines every 20mm. Grid color can also be chosen. Click the print button to print.

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Draw Regular Figure This utility will draw regular figure like triangles, squares, pentagons, hexagons and many other figures. You may draw these figures in three standard sizes (large, medium or small) or alternatively specify the side length of the figure. In the example below a hexagon has been drawn with sides of 50mm length.

In the next example we use the counter control to set the number of sides to 12 and set the side length to 40mm to draw a 12 sided figure. The figures may be printed by mouse clicking the print button.

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Draw index Wheel Most lathes have some indexing capability, which may or may not be adequate for your needs. If you wish to construct your own indexing wheel this utility will print for you an indexing wheel template which may be pasted on appropriate MDF or PLY stock to assist you to manufacture your own indexing wheel. The options on the left side of the screen will draw wheels with different divisions. Select the number of segments required and then click the print button to send to the printer.

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Print Preview

The Print preview button will output the data table, stock list and 2D drawing of you project to the screen. You may print the preview by clicking the Printer Button on the preview screen.

Settings Command

Click the settings icon to open the settings window.

Linking number of segments and mitre angle Click the check box to link number of segments and mitre angle. This is generally true for closed segmented projects. In open segmented projects it may be desirable to not link these two values. If you link the number of segments and mitre angle the software will automatically generate the mitre angle when you enter number of segments and vice versa.

Stock Calculations This setting influences the calculation of stock lengths by grouping timber widths within the given value. For example, if one ring is to be cut from 40mm wide stock and another ring from 42mm wide stock it is most likely that you will use the 42mm wide stock for both rings – assuming both rings are to be made from the same timber and from the same thickness. Specify a value, like 5mm to allow the software to group similar timber widths of the same timber and timber thickness in determining the stock list.

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Draw 3D Model Axis When rendering the 3D model you can choose to draw or not draw the 3D axis. The model below is draw with the X, Y and Z axis present.

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Use Tan or Sin ?

Basic trigonometry is used to calculate the length of a segment for any given ring. In most circumstances the Tan trigonometric ratio is used. It may be useful at times to use the Sin ratio. The diagram will assist in demonstrating the difference. The length AB is half the segment length. Length oA is the radius of the ring and angle a is the mitre angle. Therefore, the segment length L (twice the length AB) can be expressed by the formula; 푳 = ퟐ ∗ 푹풂풅풊풖풔 ∗ 푻풂풏(풂) Using the Sin ratio we employ the slightly smaller triangle oA'c. By the inscribed arc, representing the segment ring, you will notice that the length oc is the same length as oA which we have determined to be the radius of the ring. Hence, the slightly shorter segment length L’ (twice the length A’c) can be calculated by the formula; 푳′ = ퟐ ∗ 푹풂풅풊풖풔 ∗ 푺풊풏(풂) In practical terms, the difference between L and L’ is in most cases of the order of a few millimetres, creating a slightly smaller ring when using the Sin ratio. If segments of a different length are used in the same ring, it is better (more accurate) to use the Sin ratio for all the segments in the project rather than the Tan ratio. If the segments are of different length or if different timbers are used in the same ring, they must be shown as separate rows/lines on the Segmented Helper grid.

Working in stages One of the advantages of segmented turning is that the work can be done in stages. For example, a deep hollowed urn is much easier to turn if the top and bottom parts are turned in two stages. A sacrificial piece of MDF or scrap timber can be glued to the top to enable the top section to be attached to the chuck. After the top and bottom section have been turned and sanded, the two sections can be joined and any irregularity in the joint can be sanded and merged. The sacrificial piece at the top can then be removed.

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The TOOLS menu command The Tools command of the menu bar at the top of the Segmented Turning Helper software exposes various useful features. These are explained below.

Set Column Values In many projects the timber name/color, mitre angle, number of segments, timber thickness may be the same for all rings in a project. In these situations you may set the value for every row in the table (corresponding to every ring in the project) to the desired value.

Timber/Color Click Tools, Mouse over Set Column Value, then click Timber/Wood Color. This displays the window below where you enter the timber name color in the value box. Click the OK button. The Timber/Color column in the data table is filled with the specified value.

Number of Segments

In a similar way you can fill the number of segments column. Click Tools and then click Number of Segments menu item. Enter the number of segments value. Click OK. The number of segments column of the data table is filled with the given value. Similarly, for Mitre Angle and Segment Thickness

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Set Number of Rings The Tools/Set Number of Rings menu item will allow you to change the number of rings in an existing project. Enter the new value and press OK. If the current project has more rings than the new value rings at the bottom of the table will be removed and if any data was present for those rings it will be lost. For example, if the current project contains 20 rings and you modify the project to contain 18 rings, the bottom two rings, ring 19 and 20 will be discarded.

Select Project Image Click Tools/Select Project Image to select an existing image to associate with your project. Note: In the absence of your own image a default image of a segmented bowl is displayed, as shown below.

You may use the Select Project Image menu item in Tools, or as suggested by the prompt at the bottom of the default image, click the right mouse button on the image to display a context menu, as follows;

The two context menu commands allow you to remove the existing image or add a new image. Images of your projects or related images should reside in the Projects\Images folder. Usually, the full path to the images folder will be; C:\Program Files (x86)\Segmented Turning Helper\Projects\Images

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Please note: The installation software can be downloaded from my personal website; www.johndistefano.com.au Once you have download the installation module, run it to install Segmented Turning Helper to your Windows computer.

The software is free of charge and should be employed for private use only, and not for commercial profit.

This completes the software documentation. The following pages discuss some general features of segmented turning and table saw use.

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Cutting Segments For readers who are new to segmented turning please continue to read the rest of this document as it provides information and tips for cutting your segments. The description below employs a table saw and assumes that you are capable of using your table saw effectively and safely.

Cutting Accurate Angles The most crucial part of segmented turning is getting your rings to fit accurately without gaps between the segments. You can make perfect rings only if you cut very accurate angles and lengths. Segments can be cut on a band saw, with a drop saw or most accurately with a table saw. Using a table saw is the preferred method as it provides most accuracy. You can use a high quality mitre gauge to help get the angles right or you can construct a sliding table for various commonly used angles, such as 15, 10 and 7.5 degrees. Using a high quality saw blade will also reduce burrs and tears. Photo 1 shows the sliding table on the left specially constructed to cut 15 degree mitre angles and a second Photo 1 Depth Gauge to Measure Vernier Length sliding table on the right to which a depth gauge has been affixed to act as a stop whose position can quickly be adjusted. Because of the geometry of the situation, the vernier length is slightly shorter than the segment length. The vernier length corresponds to the height of the superimposed triangle (the perpendicular distance between the table saw and the stop). The segment length corresponds to the hypotenuse of the triangle. The mathematics relating these two values is; Photo 2 The Vernier Length VernierLength = SegmentLength * Cos(Mitre Angle) Initially, the depth gauge is extended to meet the blade and the readout set to zero. For each ring set the depth gauge to the calculated vernier length. The Segmented Turning Helper software calculates both segment length and vernier length values. You should use the vernier length value in setting the cutting distance for the segment. This distance could be measured off with a ruler and your own stop clamped in position. Other arrangements are also possible but some simple to use device should be built to enable the vernier measurement to be set quickly and accurately. The photographs above show what I built.

Gluing Rings If you are cutting your segments accurately you can glue the whole ring at once. Otherwise glue half ring sections together. When dry, check the matching ends of the half circles and square the ends on a disk sander, using 120 grit disk, if necessary. PVA, polyvinyl acetate glues are very common and very good for gluing wood. You could also use Titebond II which sets relatively quickly. Apply the glue to the face being glued preferably with a small brush. Bring the corresponding segments together, slide the two segments being glued, once or twice, and fix into position by bringing the two points of the segments together accurately. Completed rings or half ring should be left to dry for 4 to 6 hours before being handled. When gluing segments I use non-stick baking paper allowing the paper to be easily peeled off when the assembly of segments is dry. The underside of the ring, that is the side which will be glued onto the base or a previously assembled ring should be inspected and cleaned of any excess glue or

Segmented Turning Helper Page | 21 unevenness. Sanding of the bottom of the ring may be required if the ring is uneven. I use a belt sander to do this. The two surfaces being glued as you begin to stack your rings should be perfectly clean and flat. Depending on the overall height of the object it may be possible to glue and stack all rings to completion before you start to turn the object. For a tall object, like an urn or vase, it may be preferable to stack some rings and turn the partial object before stacking more rings.

Turning the Bowl Turn your bowl or vase progressively as you stack the rings. My preference is to glue three or four rings at a time and then turn both the inside and outside of the object, as shown in photo 3.

Photo 3 Partially Turned Bowl

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References: Woodworking For further information about cutting segments refer to Alan Mc Naught’s article, Cutting Segments on a Table Saw, Australian Woodworker, July/Aug 2013, Issue No 170.

Software The camera controller, in the 3D modelling component of the software, which provides for rotation and zooming of the model, both with mouse and keyboard, was provided from Rod Stephens book WPF 3d. Thanks Rod for an excellent piece of code.

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