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Copyright © 1998 Taras Plakhotnichenko
Most recent revision 3 March 2003
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How to manufacture a home-made recurve bow
(The original article appeared in FIDO.RU.WEAPON.)
This article aims to share with you my experiences in constructing a home-made bow, some more successful than others. The basis of the design is a recurved composite (laminated) bow, now in common usage, perhaps with the exception of so-called traditionalists. A recurved bow's arms incorporate a double curve, in which the ends of the arms bend away again from the main curve, resulting in the "re-curve". (In my opinion, the recurved bow is gradually replacing the compound bow in use, but that is beyond the scope of this article.) The bow described here has a draw weight of about 11kgs and a maximum draw length of 71cm. On to the construction!
The most difficult part of the project is the making of the arms. The basis of the construction are thin sheets of white ash veneer, 0,6mm thick, such as is commonly used in the Furniture or Shopfitting industries. Additionally, an epoxy resin and hardener, or catalyst, was needed, in the quantites of 0,5kg and 0,25kg respectively. These are not mixing proportions, but overall quantities I used. The mixing proportions will depend on the type of epoxy resin used. My next step was to build a heat box, of dimensions 74 x 30 x 40cm. It had a removable cover, and had installed in it two100W electrical bulbs as a heat source, which kept the box at about 60-70 degrees C without any special regulation.
Following this, I made a mould for the limbs. I used a wooden block of 66 x 10 x 4 cm, sawn into two sections to make the puncheon and matrix of a forming press. The path of the sawing track, if you take a measurement every 2 centimeters from the edge of the block are:
(Include sketch here) The next step is to make a wooden wedge as the core of the bow limbs. (The part of the limbs which will eventually attach to the riser) With the help of a steel metre ruler and a sharp blade, five sheets of 45 x 65 mm are cut from the ash veneer and then bonded together with the epoxy resin. It is important to de-grease the wood with acetone prior to bonding. Moisten the sheet surfaces thoroughly with the resin to form a stable bond. The whole lot is now pressed firmly together between two wooden boards, using G-cramps to apply the pressure. I placed the whole thing in a heatbox and kept it there for 5-6 hours at 60 degrees C. You may ask why I didn't use ash or maple in a single board? The fact is it's hard to get a decent unidirectional wood. Because of this the wedge would be rather weak when bending it.
Now we come to the most difficult part of the wedge process, which is producing a 1,5 x 3mm wedge out of our composite board. Having given it a lot of thought, I came up with the idea to make a special jig in which to plane it to shape. Imagine a wooden board 120cm long and 10cm width with two duralumin profiles (like "r" in a shape) at the edges fastened at a certain angle to the block surface on which our work is placed (the degree defines the angle of the wedge). An electric plane sliding on and guided by these profiles will remove progressively more wood as it moves along the jig. (The knives of the plane must be set as short as possible for the first runs.) In short, the result was fairly good. First you should practice on some spare wood, of course.
Now that's done, lets move to the next phase.
The question now arose : What do I use to armour the wedge? I tried in vain to get real unidirectional fibreglass, eventually coming up with an alternative - a plastic used in the electronic industry for installing electronic components (Printed Circuit Boards - fiberglass cloth moistened in epoxy and pressed), which I got at a hobby shop. Normally it is 1mm thick. Using Tinsnips I cut two strips that had the same dimensions as the strips from the previous phase. I roughened each strip with sandpaper on one side. I also cut two additional strips of veneer. I now had 5 components: a wedge, two strips of veneer, and 2 fiberglass strips. Having thoroughly covered all the surfaces with glue, I put all the elements together in the following order: in the middle the wedge, on every side of the wedge two strips of veneer, and on top, inwards and outwards - two fiberglass strips. I placed the whole thing into the mould, pressed it with G-cramps, and put the mould, in turn, into the heatbox. By the way, the inner surface of the mould should be covered with something pliable - such as strips of rubber - to allow the pressure to equalise over the whole surface. I now had an almost complete limb. The procedure is repeated for the other limb. All that remained to be done was to saw it to shape its width. The limb dimentions are:
Length (along the surface): 550 mm Width (near the handle): 33 mm Width (125 mm from the limb tip, along the surface): 23 mm Thickness (near the handle): 6 mm Thickness (near the limb tip): 3 mm
The wooden handle with a gap (for an arrow to pass through) like those handles of sport bows:
Length: 315 mm Width: the same as the limb Thickness (in its thickest part): 50 mm The gap is 35mm form the center of the handle The angle of limbs to the bow is about 10 degrees. I fastened every limb to the handle with two bolts "M6". At the end of the limbs I glued small wooden pieces for reinforcement and made grooves for the bowstring. The bowstring is made of kevlar (Taras - Not Dacron?).
In general, that was "a challenging experience" as Englishmen say. I concluded that the fibreglass substitute I used was not sufficient, as it did not provide a decent draw weight. It also started de-laminating at the inside of the limbs. Proper fibreglas s must be used. Just take care when sanding or sawing, as fibreglass dust is very hazardous to one's health. Always use a respirator. You can try to make real fiberglass yourself using fiberglass roping - a rope consisting a loosly knit glass fibers used in shipping and yacht industries. Moisten the fibers with glue, firmly remove excess glue from fibers, passing it through two rollers or something like that, and place it in the matrix (pictured above). Don't foget to add a plastisiser (debutilftalat - a transparent odourless liquid) to the glue (10-15%). The surface of the form must be wrapped with something like cellophane otherwise the fibreglass will bond to the form. Cover it with a puncheon (not very firmly - the glue must be able sqeeze out) and place the mould into a heatbox.
The end. Russian Archery Ring (c)