Introduction: How to Make a Custom Bow Grip Using a Balloon and Some Flour

About: Maker, engineer and researcher at the National Research Council of Italy. Generally I'm interested in the topics of Indoor Environmental Quality and its interaction with energy efficiency, 3D printing, open ha…

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Recently I followed the archery course at the "Arcieri Minerva" company. During the course we learned to distinguish the bow grips in three different types: low, medium, high. Many archers customize the bow grip with the adhesive tapes such as those that surround baseball bats or rackets. Some others use different type of resins. I also have felt the need to change the grip which is mounted on my bow and below I explain first why this change was necessary, and then how I realized the new grip using a balloon and flour (Yes , you got it right!).

Step 1: Grip: Default Vs Custom

The grip below is the one mounted by default on my riser, a Win & Win Pro Accent Carbon. It does not suit my style at all because it was too low and narrow. Most important thing is that the rounded parts do not allow me to hold the bow in the same way: I have no point of reference within the palm of the hand.

I would have preferred a bow grip thicker and higher, without curvature at the top.

As you can see from the photo, although I have entered the blue thickness between the original grip and the palm of the hand, the hand position is still correct: it is tilted about 45 ° with respect to a hypothetical vertical plane and the center of the "V "determined by the hypothetical lines represented by thumb and index finger is positioned on the center of the grip (corresponding roughly to the center of the bow) and the pressure is exerted on the muscle that extends from the base of the thumb to the wrist.

The blue thickness, adaptable because it made with a balloon filled with flour (alternatively you can use the plasticine) allows me to have a more natural position with further reference points on the remaining part of the palm that is not directly involved in the shooting phase and that is not affected by the pressure exercised. It contributes to challenge the arc always in the same way.

Step 2: All That Is Necessary

Below I explain how you can realize your personal grip using some flour, a balloon and Additive Manufacturing (AM) and 3D scanning techniques. Through this method you can create a customized grip that is able to "fill in" perfectly the palm of the hand: you can take inspiration from the details below. As you have already seen, in all the photos is shown my twitter account: @frank984. You can use it to contact me for any further information.

Before proceeding, it is worth pointing the material that you must have:

· A photocamera (a smartphone could be useful);

· A ballon and some flour (alternatively the plasticine);

· A 3D printer (optional).

The software that are necessary are:

· 3D meshes generator (ReMake for example) ;

· 3D CAD software (Rhino for example);

· G-code generator software for 3D printers (Slic3r for example).

The procedure that leads to the creation of the personalized grip is splitted in the following steps:

1. creation of the mold;

2. realization of the photos;

3. creation of the mesh or polysurface;

4. creation of the 3D model;

5. .gcode creation and 3D printing;

6. installation on the riser.

Step 3: 1. Creation of the Mold

You have to fill the balloon with flour (if you do not know how to do it you can watch this video) and then shape it by creating a real cast of the palm of your hand.

Step 4: 2. Realization of the Photos

Once you have done the cast, we proceed to 3D scan using the technique of Structure-from-Motion (SFM) that allows you to automatically reconstruct a three-dimensional model from a series of two-dimensional digital images (I assumed you have not a 3D scanner). You need to take pictures all around the imprint. you must not take pictures in high resolution, the important thing is that the object is well illuminated without shadows. For the purpose I used a rotating plate and my Nikon placed on a tripod as in the picture.

It should be noted that an expert modeler could bypass the SFM method: it is not suitable for impatient people. He can directly reconstruct the polysurface considering only two photos.

Step 5: 3. Creation of the Mesh or Polysurface

Once you realized the photos you need to use a specific software. There are different sw available also completely free. I used Remake that in the free version allows you to upload up to 50 photos. Because the object to be scanned is small , 50 photos are enough. Once loaded the images, Remake creates the mesh, and then you can sculpt and smooth it, reduce the number of triangulations (I reduced them of 70%) and export the file in .stl format.

Step 6: 4. Creation of the 3D Model

Once the mesh It is made, it is necessary to import it into a 3D modeling software. Even in this case there are several options. Autocad, Rhino or Sketchup (undoubtedly the latter is more simple and suitable for newbies) are just some of the available software. Once you have imported the .stl files you can work on mesh and shape it up to get the 3D model of the grip. I report some examples.

In step 2, I mentioned to the polysurface creation process considering only two photos of the mold. The modeling of the polysurface following this approach is not suitable for beginners but it allows to obtain satisfactory results. In practice, you have to take two pictures, considering a horizontal and longitudinal sections. The mold is divided in 4 parts given by the intersections of the two photos. You can draw the contour lines and then create the slices of different surfaces starting from the control lines. The same for the riser. The grip is obtained by the boolean difference between the two solids.

I have realized the 3D model of my custom bow grip with this second approach. It is high with two net cuts, one in the lower part, the other in the upper part.

Step 7: 5. Gcode Creation and 3D Printing

Once you have realized the 3D model you have to export it in the .stl format and then import it into a software for the generation of the .gcode file. I used Slic3r. The .gcode file is recognized by all the 3D printer. If you do not possess a 3D printer you can use web service like 3D Hubs or go to a neighbor FabLab.

Note that I opted for a a honeycomb fill type with filling ratio of 20% that would ensure good compressive strength and low weight: the 3D printed molded part in flexpla weighs less than 40 grams.

Step 8: 6. Installation on the Riser

Once you printed the part you can install it on a riser as any other grip.

The custom grip fits perfectly with the palm of the hand. The life line fits perfectly with the edge of the grip.

The edge of the riser borders with the upper edge of the hand and the thumb is collocated in the hollow of the grip perfectly.

Step 9: Conclusions

The advantage of using this technique is that the new custom grip guarantees absolute repeatability with no margin of error because every time you hold the bow you have 3 reference points. In addition you can also consider the psychological factor due to the realization of this improvement.

To think of it the manufacturers of bows could make available a customization service, providing printing and installation of the custom grip after sending the 3D model file.

Finally, you have to note that these instructions are released under the CC-BY license so you are free to: copy and redistribute the material in any medium or format, transform, and build upon the material for any purpose, even commercially. You must only give appropriate credit.

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