 Manufacturing a Synthetic BowEditor’s Note Mehmet Gölhan has been practising modern archery with a olympic recurve for years now. He has built us a spine tester in the past and recently he has excelled himself and built a Turkish traditional bow replica from synthetic materials. A Turkish bow is a composite of organic materials. It usually takes 1 to 3 years to build one due to the long drying times of organic glues. By using modern synthetic materials, replicas are built faster and they appear on the archery market more often then ever. These bows are inexpensive, are not sensitive to atmospheric conditions, are more consistent and user friendly. The design of Gölhan’s bow is based on museum studies on original pieces and many photographs. He experimented with various materials and techniques for a year and in January of 2009 he built his first synthetic Turkish bow replica with the basic morphologic features of the Ottoman-Turkish bow. Below you will read how Gölhan has built this excellent replica.
The first synthetic Turkish Bow Replica Written by: Mehmet Gölhan Preparing the mould The first stage was to prepare a model of the bow I was planning to built. From this model I would obtain the mould. I used wood and polyester resin to build the model. The model was just half a bow consisted of one limb and the exact half of the handle. This way I would save time and guarantee a perfect symmetry on the whole bow. I screwed the model on to a 3 mm thick aluminium plate that I had bent previously into the shape of a bow. Before obtaining a mould from a model, I would like to underline some important points: 1- The bow model should be very close to the desired final product in shape. 2- To be able to remove the final product from the mould, the cross section of the model should be conical and there should be no bulges or alike that could prevent the product from being removed. 3- A thin layer of epoxy resin should be applied over the surface of the model, using a sponge. Obtaining the mould from the model 1- To prevent the model from sticking to the mould material, the surface of the model is polished and waxed. And then a commercially available seperator agent, known as “PVA” is applied on the whole surface of the model. 2 A polyester and fiberglass layer of 3-4 mm thickness is then applied on to the treated surface. 3-After waiting for 1-2 days for the polyesther to set, the mould and the model are seperated by using triangular wooden wedges. 4-The surface of the model is checked for residual PVA and wax, and the surface smoothness is checked. If needed, the model surface is washed and cleaned with warm water. Now the model is ready to be used in moulding the other half of the bow. 5-Now the two seperate limb moulds are fixed together using two connection pieces. The materal that is going to form the limbs will be poured into this two piece mould. The connecting pieces also help the seperation of the set material from the mould.
Back: The bow model Front: The mould of a single limb
The bow model (left) and two limb moulds (right) Manufacturing the bow For safety reasons the following procedures should be done using rubber gloves and a protective mask. Also a venting device would be helpful to eliminate fiber dust from the working environement. 1- The two pieces of mould are fixed together to form one bigger mould and the inner surface of the mould is insulated by applying wax and PVA on the whole contact surface. 2- Ideally, one should inline the mould with a single piece of fiber and apply polyester over it. But due to the physical properties of fibers, it would be a very laborious and precision task. For practical reasons it is advised to lay out the fibers inside the mould from the tip to the handle, overlapping half the handle. 3- The fiber is laid out starting from the middle to the sides and then polyesther is applied. The material should be applied with vertical brush strokes to avoid bubble formations. The fiber should be one piece, otherwise the finished bow may not withstand the tensions applied during functioning. 4- This procedure is repeated until the fiber-polyester layer builds upto a thickness of 5-6 mm. This thick synthetic material should provide a draw weight of 40-45 lbs at 28 inches of draw. 5- Once both limbs are done, one must for the material to set. It is essential to follow the instructions to be found on the material packaging in order to determine the setting time. Make sure that the two moulded limbs are completely set. Then seperate the mould by removing the connection pieces, and free the limbs from the mould.
Above-Two moulds connected to form one mould and connection pieces
The bow removed from the mould Finishing the Bow The bow removed from the mould has an extremely irregular surface. First the surface of the bow is sanded with coarse and medium grit sand papers. The surface shape is given by a concave scraping tool. This tool is prepared by carving a piece of wood to the desired concavity and glueing a sand paper on it. During finishing, extreme attention should be given to shape the two limbs exactly the same. The amount of sanding should be even and symmetry must be achieved. The tips and the string nocks are prepared during this phase. Heat-treating to Complete the Polimersation Heating is necessary to ensure the complete polymerisation of the fiber-polyester composite. The heater is a wooden box with a lid , large enough to hold the bow and contains 4 light bulbs, each 35-40Watts. The bow is heated for 5 to 6 hours and after the process the bow gets even stiffer.
The heater designed to complete the polymerisation of the synthetic material.
Tillering Procedure A well functioning bow is only possible if both limbs are symmetrically shaped and bend symmetrically during functioning. At this stage the bow is drawn on a tillering tree and tuning begins. Here, one reaps the benefits of having paid attention to symmetry at the shaping and finishing stages. With the help of the notches on the tillering tree, one can observe the symmetry as the bow is gradually drawn. If there is no symmetry, the belly of the bending section (sal) is sanded with the concave sanding tool. This continues until the 28 inches of draw is achieved. The bending of the limbs should be checked from all directions. If the tips are twisted to one side, the opposite side of the belly should be sanded. The twist indicates that one side of the limb is weaker than the other side.While the bow is gradually drawn to 28 inches, the tips and bending sections are checked and sanded. This check-and-sand procedure should be continued until the two limbs are symmetrical and the bow bends symmetricaly, without twisting.
The bow drawn gradually on the tillering tree and the limbs are tuned
Covering the bow Before covering the bow I have shot the bow a few times and checked the tips and bending sections. In order to keep the string safely inside notches while shooting, the surface where the string loop and the end of the bending section meets must be flat. The curvature should end where the bending section ends. After making sure that the string notches hold the string in place, I have covered the back of the bow with leather and the belly with synthetic sponge and leather.
Covering the back and belly of the bow. tirendaz bow in action:
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