Windsurf Board Fins, 2-Sided Machining

In this project Michael Wazenski of, Annapolis MD machines 8 windsurf board fins in two setups (top and bottom). These are not just any fins – Michael’s world class fins are machined at and sold by Tectonics Maui, a confirmed leader in windsurfing boards and gear.

Read the full case study here.

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The stock material is G-10, a fiberglass epoxy composite, the same material used to manufacture printed circuit boards. In this example each fin measures 187 x 177 x 11.12 millimeters. Each fin component consists of the fin foil – this is the portion that extends out of the board and makes contact with the water. Extending below the fin foil is the insert block, referred to as a US Box. This is the portion that is mounted within the board proper and is fixed in place with mounting screws. Both the fin foil and the US Box block are machined together from the same stock as a single component. The fin foil component is shown here and is dimensioned below.

On the left we see the completed fin foil component with some basic dimensions. The fin foil is the portion that extends below the windsurf board and the US Box block is the portion that is insert-mounted into the board. The component is 187.13 x 177.00 x 9.40 millimeters. 

Part and Setup

The RhinoCAM Machining Job tree for Side A shown below on the right. It consists of the Machine, Post, Stock and Fixture definitions as well as each machining operation (MOp). The Machine Coordinate System origin is located at the X,Y,Z center of the stock block. Three 2 Axis Facing operations appear first under Steup 1. These are followed by one Machining Operation Set (MOp Set) that contains each of the eight 3 Axis Parallel Finishing operations. The remaining 2 Axis Profiling operations cut the perimeter of the US Box block and the receding edge of each fin. All operations are cut using a ¼” (6.35mm) diameter Corner Radius Mill with a corner radius of 0.762mm. See Sequence of Operations below for Side B.
(A) The physical CAD geometry setup contains 8 fins arranged within a stock perimeter of 464 x 560 x 12.8 millimeters. Each fin is a 3D solid model.
(B) The Machining Job tree shows Setup 1 for Side A containing 2 and 3 Axis machining operations. The MOp Set contains the 8 3 Axis finishing operations.

Sequence of Operations

This part is machined (top and bottom) with the same setup. The Machining Job and Setup 1 shown above will machine Side A of the stock. 2 Axis Facing will cut the tops of the US Box blocks, followed with 3 Axis Parallel Finishing that cuts side A of the fins. A 2 Axis Profiling operation is then used to cut the perimeter of the blocks down to the mid plane. 

At this point the stock is flipped over and realigned with the stock mounting screws on the CNC router. For Side B, the top facing of the US Box blocks and side B of the fins are then machined from g-code posted from the same Setup 1. To complete the process a 2 Axis Profiling operation will clear the perimeter of the fins while a final Profiling operation cuts the remaining perimeter of the US Box blocks, thus releasing the 8 fins from the stock. Note that for Side B, the control geometry remains the same and more importantly, Catch Surface B (see Control Geometry below) remains at -0.762 below the mid plane. 

Control Geometry

The two images below illustrate the positioning of the part and related control geometry. Make note of the location and elevation of Catch Surfaces A and B. Catch Surface A is positioned at the Z 0.000 mid plane of the part and controls the elevation of the cut start point. Catch Surface B is positioned at -0.762 below the mid plane.

Catch Surface B allows the cutting tool to drop below the mid plane by 0.762mm which is the same value as the corner radius of the cutter. This means that the full cutting diameter (6.35mm) of the tool is located at the mid plane. The width of Catch Surface A and the extension of Catch Surface B past the fin need only be a minimum width equal to ½ x the tool diameter. In our illustrations they are shown at a width of 6.35, the full cutter width.

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(C) The CAD geometry includes the fin and US Box block (grey) , catch surface A (green), catch surface B (brown) and 2D planar curves (red).
(D) Here you see an elevation view with catch surface A located at the midplane (Z0.000) and Catch Surface B positioned at (Z-0.762) which equals the radius of the cutter.

2 Axis Facing

As mentioned above the machining operations in this setup include both 2 Axis and 3 Axis strategies. The 2 Axis Facing operations (shown in image E below) are controlled by the perimeters of the US Box block geometry defined as Part Regions and with the perimeters of the catch surfaces defined as Avoid Regions. For Facing the spindle speed is 6,300 RPMs with a cut feed rate of 2,000 mm/minute. With a linear cut pattern and mixed cut direction the tool steps over 1.58mm per pass, at one level, with a 10 degree ramp entry.

3 Axis Parallel Finishing

All 3 Axis operations in RhinoCAM are gouge-free. This means that the cutting tool will not violate any surface as long as it is visible at the time the operation is generated. A 3 Axis Parallel Finishing operation is used to cut each side of the eight fins. The selected control geometry for this operation are the perimeter edges of Catch Surface B. Catch Surface B is a planar surface that extends out past the perimeter of the fin by 6.35mm. The cutting tool will follow the fin surfaces and then drop onto Catch Surface B and stop at its perimeter. This is best illustrated in the elevation Image (D) above.

The spindle speed for this operation is 6,300 RPM and a cut feed rate of 5,500 mm/minute. A mixed cur direction, a cut angle of zero degrees (along the X Axis) and a stepover of 0.5 is applied. The cut time for each fin is approximately 3 minutes. You can refer to the Machining Information section below.
(E) 2½ Axis Facing operations are used to planar cut the up-facing sides of the US Box blocks. The US Box blocks and fins are one 3D solid.
(F) 3 Axis Parallel Finishing operations (one for each fin) are used to finish cut the fins on one side. This toolpath extends past the fin surfaces to the perimeter of catch surface B.

2 Axis Profiling

The final cuts in this setup include two 2 Axis Profiling operations illustrated in Image G below. One for the US Box blocks perimeter and another for the trailing edge of the fin surfaces. The control geometry for these operations are open and connected merged curves. The spindle speed for these operations is 6,300 RPM at a cut feed rate of 600 mm/min with a stock allowance of zero. 

A 10 degree ramp entry is used with a mixed cut direction. The US Box block perimeters use two cut levels, the second level being at 4.5mm below the mid plane. The fin trailing edge perimeters are cut at 1,000 mm/min with a stock allowance of 0.1 and one cut level that stops at the midplane. You can see the cut material simulation of all operations in Image H below.

(G) 2 Axis Profiling operations cut the perimeter of the US Box blocks and the receding edge of each fin. Note the 10 degree ramp entry and two cut levels.
(H) Here we see the final cut material simulation of Side A showing the 3 Axis Parallel Finishing, 2 Axis Facing and 2 Axis Profiling operations.

Machining Information

The machining information for this setup is shown in the RhinoCAM dialog below. Note the Cut Feed, Spindle Speed and the # of GOTO motions for each operation, the largest being Fin 4A at 62,400 motions. The total machining time is estimated to be 1 hr and 26 minutes. This is based on the accumulated cut feed rates for each operation plus the transfer feed rate which is set to 200% (2x) the cut feed rate.
(I) The machining information for this setup is shown in this RhinoCAM dialog. Note the Cut Feed, Spindle Speed and the # of GOTO motions for each operation, the largest being Fin 4A at 62,400 motions. The total machining time is estimated to be 1 hr and 26 minutes.
(J) Here we see a view of Michael’s RhinoCAM tool library in an Excel spreadsheet format. This same tool library is programmed into his Centroid controller. While he does not have an automatic Tool Changer, his Centroid controller let’s him know prior to each program run, exactly what tool to load to minimize confusion.

Machining & Assembly

The images below show Michael’s custom wave fins being machined on his Centroid controlled CNC 3 Axis router on the left (watch this short cutting video here). On the right we see a set of 4 custom wave fins assembled on a multi-fin windsurf board. A mini-tuttle block, an alternate fin base standard is insert mounted within the board proper and fastened using screws fed from the top side and through the board.
(K) Here we see Michael’s Centroid-driven CNC router cutting a set of prototype wave fins from G-10 composite stock material.
(L) Here we see a set of 4 wave fins assembled on a typical windsurf board. The inserted mini-tuttle blocks are mounted into the board and fastened with screws.

— Cool project, Michael! Thank you for allowing us to showcase your work!–

More about CNCFins

Michael Wazenski is a Systems Engineer with Northrop Grumman in Annapolis MD, overseeing systems integration projects on some of the most advanced satellite systems in the world including the JWST (James Webb Space Telescope). By night Michael, and his business partner Keith McCulloch operate where he designs the CAD and CAM data to manufacture his custom windsurfing board wave and weed fins. These are not just any fins – Michael’s world class fins are machined at and sold by Tectonics Maui, a confirmed leader in windsurfing boards and gear. You can purchase Michael’s wave fins at Tectonics Maui (see below).

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More About Tectonics Maui

Dennis Parton, Owner/Operator of Tectonics Maui has over 25 years of experience, designing world title winning windsurf fins for many of the top professional windsurfers on the PWA World Tour. This heritage has led him to the development of the finest G-10 fin production facility on the planet! Their machines and software are state of the art and Tectonics only uses the finest, hand selected panels of G-10 composites available on the market.

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Don LaCourse

Don LaCourse

Don LaCourse is an Application Engineer with MecSoft Corporation. Don brings over 20 years of experience in CAD/CAM operations in both automotive and mold design applications. Don also has extensive experience in documenting CAD/CAM products and is actively involved with writing the on-line help as well as creating training tutorials for MecSoft's products.
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