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Segmented Turning Helper Page | 1

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…


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.


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.


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.


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.


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.


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.


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.


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


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.


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.


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.


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.


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.


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.


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.


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;

𝑳 = 𝟐 ∗ 𝑹𝒂𝒅𝒊𝒖𝒔 ∗ 𝑻𝒂𝒏(𝒂)

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;

𝑳′ = 𝟐 ∗ 𝑹𝒂𝒅𝒊𝒖𝒔 ∗ 𝑺𝒊𝒏(𝒂)

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.


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


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


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.


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

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;

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

Photo 1 Depth Gauge to Measure Vernier Length

Photo 2 The Vernier Length


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


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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