Carbon Fiber Recurve: Diy Guide

Carbon fibre recurve bows are highly sought-after by archers for their lightweight and durable qualities. While wooden bows have been the traditional choice for bow-making, carbon fibre has emerged as a popular alternative, offering enhanced stiffness and resilience that better suit modern strings. The process of crafting a carbon fibre recurve bow involves cutting and laminating prepreg carbon fibre, moulding it into shape, curing, sanding, and finally, engraving and assembling the bow. With its superior performance characteristics, carbon fibre has become the primary choice for many serious archers, revolutionising the sport and challenging the dominance of traditional wooden bows.

Design the bow using CAD software

Designing a bow using CAD software is a complex process that requires careful planning and execution. Here is a step-by-step guide on how to design a carbon fibre recurve bow using CAD software:

Choose the Right CAD Software

Select a suitable CAD software that offers 3D modelling capabilities and is specifically designed for creating complex shapes and structures. Examples of popular CAD software include Autodesk, Rhino, Sketchup, and Tinkercad. These software tools provide a range of features and functionalities to help you design your bow accurately.

Define the Bow Specifications

Before starting the design process, clearly define the specifications of your carbon fibre recurve bow. This includes determining the desired length, width, thickness, and curvature of the bow. Consider factors such as the intended use of the bow, the user's preferences, and any specific requirements or constraints.

Create a Digital Model

Using the chosen CAD software, begin creating a digital model of the bow. Start by setting up the dimensions and overall shape of the bow, including the riser (the central part of the bow), the limbs (the upper and lower curved sections), and the string. Ensure that you input accurate measurements and adjust the model accordingly to meet your specifications.

Add Details and Features

Once the basic structure is in place, start adding the finer details and features to the bow design. This includes elements such as the grip, arrow rest, sight, and any stabilizers or accessories you plan to incorporate. Pay close attention to the placement and positioning of these components to ensure optimal performance and comfort during use.

Perform Structural Analysis

Utilize the CAD software's analysis tools to perform structural analysis on your bow design. This will help you assess the strength, durability, and flexibility of the bow. Make adjustments as necessary to ensure that the design can withstand the stresses and forces exerted during use, especially at the joints and connection points.

Finalize the Design

After making any necessary adjustments and refinements, finalize your carbon fibre recurve bow design. Ensure that all dimensions, angles, and features are accurately represented in the digital model. Save your work and export the design in a suitable file format, such as .STL or .OBJ, which can be used for further prototyping, manufacturing, or 3D printing.

By following these steps and utilizing the capabilities of CAD software, you can design a carbon fibre recurve bow that is tailored to your specific requirements, ensuring both functionality and aesthetics.

Cut and laminate prepreg carbon fibre

To cut and laminate prepreg carbon fibre, you'll need to follow these steps:

Creating Cutting Templates

Start by making temporary paper or masking tape templates of the different shapes needed to laminate the part. Transfer these temporary templates to the prepreg and cut them out using a sharp knife. Prepreg can be cut with scissors, but the resin tends to build up on the scissors, so cutting with a knife is preferred.

Laminating the Surface Ply

Apply a release agent to the mould before placing the pre-preg. Work from the centre lowest point outwards, ensuring that the material is properly laid into the mould. Laminating tools called "dibbers" can be used to press the pre-preg into the mould. Take care not to bridge over any corners or details. For tight corners, make small cuts in the material using composite snips to allow it to lap and conform to the mould.

Surface Ply Debulk

Apply a layer of perforated release film and a layer of breather cloth to the mould. Place the mould into a vacuum bag and pull a vacuum for at least 10 minutes to complete the debulk process.

Laminate the Backing Ply

The backing ply is thicker and harder to laminate, but the process is the same as for the surface ply. Ensure there is no bridging over the mould detail and corners. For this part, only one backing ply is needed, but for bigger and thicker parts, you may need extra plies.

Vacuum Bagging and Curing

Apply a non-perforated release film to the pre-preg, pressing it carefully onto the mould surface. Use flash release tape if necessary to hold the film in place. Drape the breather cloth over the underside and edge of the part to provide an air path. Place the mould into the vacuum bag, pulling only a partial vacuum at first to position and reposition the bag. Once you are happy with the positioning, pull a full vacuum.

Oven Curing

Place the vacuum bag carefully into the oven, ensuring it doesn't snag or catch on any edges. Connect the vacuum line inside the oven and run the pump to maintain full vacuum throughout the cure. Program the desired cycle on the oven.

Demould the Finished Part

Allow the part to cool to room temperature before attempting to demould. Remove the bagging film and breather, then use demoulding wedges or pointed items to carefully prise the edges of the part away from the mould. Trim and finish the edges of the carbon fibre part with a suitable rotary cutting tool.

Cure, cool and sand the raw stick

To cure, cool, and sand the raw stick when making a carbon fiber recurve bow, follow these steps:

Curing the Bow:

Firstly, it is important to understand the curing process. Curing carbon fiber involves using heat to activate the resin that binds the fibers together, resulting in a strong and rigid material. The curing process typically involves placing the carbon fiber in a mold and applying heat and pressure. The specific temperature and duration of the curing process will depend on the type of resin used and the recommendations of the manufacturer. This information should be available on the resin's datasheet or the manufacturer's website.

Cooling the Bow:

After the curing process is complete, allow the bow to cool down gradually. Rapid cooling can cause thermal shock, leading to cracks or other defects in the carbon fiber. Place the bow in a well-ventilated area and avoid using a fan or other cooling methods that could cause rapid temperature changes.

Sanding the Bow:

Once the bow has cooled to room temperature, you can begin the sanding process. Sanding carbon fiber can be hazardous due to the creation of carbon fiber dust, so it is important to take the necessary precautions. Wear a respirator, safety goggles, and protective clothing to avoid inhaling or coming into contact with the dust.

Wet sanding is recommended to minimize dust. Use a fine-grit sandpaper, such as 400-grit, and sand the bow gently in the direction of the fibers. Avoid using too much pressure, as this can damage the carbon fiber. Continue sanding until you achieve the desired smoothness.

After sanding, wipe down the bow with acetone and rubbing alcohol to remove any remaining dust or residue. Inspect the bow for any structural damage, such as cracks or deep chips. If any damage is found, repair it using a premium epoxy resin, following the manufacturer's instructions.

Finally, apply a clear coat to protect the carbon fiber and give it a glossy finish. Choose a high-quality clear coat with UV protection to prevent oxidation and degradation over time. Follow the manufacturer's instructions for mixing and applying the clear coat. Allow the bow to cure completely before use.

Check the stick's curve, weight, strength and resonance

Checking the curve, weight, strength and resonance of the sticks is a crucial step in crafting a carbon fibre recurve bow. Here's a detailed guide:

Curve:

The curve of the limbs is a defining feature of a recurve bow. When unstrung, the limbs curve away from the archer. This design allows the bow to store and deliver more energy, resulting in greater speed for the arrow. However, it also puts greater stress on the materials. When checking the curve, ensure that it follows this recurved design and that the limbs are shaped symmetrically to ensure balanced performance.

Weight:

The weight of the sticks, or the draw weight, is a critical factor in the performance and ease of use of the bow. A heavier draw weight provides more power and speed, but it also requires more strength to pull. When crafting the sticks, consider the intended user's physical attributes, such as height, build, wingspan, and muscle strength. For children, a draw weight of 10-15 pounds is suitable, while large-framed men can handle up to 45-60 pounds.

Strength:

The strength of the sticks is essential to ensure the bow can withstand the stresses of drawing and releasing the arrow without breaking or warping. Carbon fibre is known for its excellent strength-to-weight ratio, and interlocking hollow carbon tubes can provide incredible stiffness and reduce noise. When checking the strength, consider the quality of the carbon fibre used and the construction technique. Ensure there are no weak points or imperfections in the material that could compromise the overall strength.

Resonance:

Resonance refers to the vibration and noise produced by the bow when fired. A well-crafted bow should minimise resonance, as excessive vibration can affect accuracy and cause discomfort for the archer. Carbon fibre, due to its stiffness and vibration damping properties, can help reduce resonance. When checking resonance, pay attention to any vibrations felt through the bow after firing, as well as the noise produced. A well-crafted carbon fibre bow should feel stable and quiet in the hand.

Engrave the model name, hair thickness and serial number

Engraving the model name, hair thickness, and serial number is an important step in the process of making a carbon fibre bow. This step ensures that each bow is properly identified and can be tracked if needed. Here are some detailed instructions on how to complete this step:

Before starting the engraving process, gather the necessary tools and equipment. You will need an engraving machine or tool, such as a laser engraver or a hand-held engraving tool. Make sure you have the correct settings and attachments for engraving on carbon fibre or a similar composite material.

Clean and prepare the surface of the bow where the engraving will be done. It is important to remove any dust, debris, or residue that may interfere with the engraving process. Use a soft cloth and a mild solvent to gently wipe the surface. Allow the area to dry completely before proceeding.

Determine the location and layout of the engraving. Choose an area on the bow that is easily visible and accessible. Decide on the size and placement of the text, ensuring that it is legible and aesthetically pleasing. Create a template or guide if needed to ensure accuracy.

Set up your engraving machine or tool according to the manufacturer's instructions. Adjust the settings to the appropriate speed and depth for engraving on carbon fibre. Test the engraver on a scrap piece of similar material to ensure that the settings are correct and produce the desired results.

Carefully and slowly engrave the model name, hair thickness, and serial number onto the bow. Follow your predetermined layout and template, if applicable. Take your time and work with precision to ensure that the engraving is accurate and consistent.

Once the engraving is complete, inspect the work to ensure that all the information is correct and clearly legible. Run your finger over the engraved area to feel for any sharp edges or imperfections. If necessary, use a fine-grit sandpaper or polishing compound to smooth out any rough areas, being careful not to distort the engraving.

By following these steps, you will be able to successfully engrave the model name, hair thickness, and serial number on your carbon fibre recurve bow, adding a professional and personalised touch to your creation.

Frequently asked questions