Fiberglass horse bow
Submitted by Matt W.
The first step in building a laminate bow is the construction of the form. A good form will ensure even bending of a bow’s limbs, and can make the glue up process fairly simple and straightforward. To build my form, I purchased a 2X6 from home depot and cut it to 48 inches in length with a chop saw. This cost me $4.00.
After cutting the board to 48 inches, I drew out a pattern with a marker. A good way to achieve a nice smooth pattern is to use a piece of poster board to initially create and draw your pattern on. Then, cut this pattern out with scissors and use it as a stencil to draw it on to your 2X6.
Here is a scale diagram of the pattern I used for my form. In the photo, 1 square represents 2 inches. The height difference between the highest and lowest point in this form is 2.5 inches.
Using a hand held jigsaw equipped with the longest blade I could find, I cut along the lines of my pattern. I would really have preferred to use a band saw for this step because ban saws make square cuts. However, I do not have access to a band saw so I just did the best I could with the jigsaw.
The next step in building the form was to drill holes in it. This is to allow the stretch clamps to wrap easily around the form. I made the big holes with a 1.25 inch drill bit and the small holes with a 3/8 inch drill bit. I made the slots with the jigsaw. These holes are also visible in the above picture.
Since the form was cut out with the jig saw, the cut was very un-square. I used a rasp and a file to square up the top surface of the form as best as I could. The reason it is very important to have this surface be square is so that there is no twist set into the limbs during the glue-up. Here is what the surface looked like after the sanding.
The shiny look of the wood is due to the fact it is covered with packaging tape. This prevents the epoxy from sticking to the form during glue up. Many people also use saran wrap for this step.
Now that the form is complete, its time to turn our attention to the handle. The handle for my bow is going to be 1.5 inches thick. To practice I drew the pattern on the back of a 2X6.
After achieving a pattern I was satisfied with, I proceeded to cut out the shape. Of course I didn’t use pine for my handle. In my personal opinion, this wood is too soft to make a reliable handle. (I happened to choose white oak.) I laminate two .75 inch pieces together using Titebond 3 to get the desired thickness of 1.5 inches. Since I had to use the jigsaw to make the cuts, I had to laborer for a long time squaring them up the same way I did with the form. Since some wood will be lost during the process of squaring up the cuts, it may be a good idea to cut slightly outside the lines. Again, using a band saw for cutting would be better because they make a square cut the first time, and thus, they don’t require any additional sanding.
This was the result. It is important to have the tips be almost paper thin for the last inch or so to help prevent de-lamination of the bow.
(By the way the middle part of the handle stands .75 inches tall in this photo. I forgot to include this measurement in the previous diagram.)
Here is a picture of the tip.
Here are the materials I used for the limbs. I purchased them all from bowstick. Pictured from top to bottom are as follows: One 72 inch long 1 1/2 inch wide 1/16 inch thick parallel lamination of hard maple. Below that are two 36 inch long, 1 1/2 inch wide, 1/6 inch thick tapered laminations of hard maple. Then below that are two .050 inch thick 1 1/2 inch wide 72 inch long pieces of Prepreg fiberglass.
For the glue-up I cut the materials to obtain pieces of the following lengths. Two 21.5 inch pieces of fiberglass. Two 21.5 inch tapered lams. One 72 inch parallel maple lamination. One 72 inch piece of fiberglass. (I simple left the parallel maple lam and the remaining piece of fiberglass 72 inches in length. I will trim them after the glue-up).
Since the curve of my handle did not perfectly match the curve of my form, I had to do the glue-up in two different steps to ensure good glue joints. First I glued the 72 inch long pieces of fiberglass and the 72 inch parallel maple lamination to the back side of the handle. I used using West Systems epoxy for the gluing.
only glued the fiberglass and maple together where the maple was glued to the handle. Because of this, I will need to be sure to spread glue in-between the rest of the un-glued portions of maple and fiberglass when do the second glue-up. Be sure that the rough side of the fiberglass is the side that the glue goes on and that the smooth side is covered with masking tape to prevent glue from getting on it.
Here is a picture of the handle and laminations clamped up. Notice how I put a couple pencils in-between the maple and fiberglass laminations on either side of the handle. (The one on the right is barely visible behind the black and orange clamp.) The pencils were there was to ensure that the laminations did not become accidentally glued together in any place that I didn’t want them to. (In other words, the two laminations were glued together in-between the pencils, however I did not put glue outside of where the pencils are.)
Here's a better picture of the pencil between the wood and fiberglass.
This is the order the materials get glued up in on the form from Bottom to top. 72 inch fiberglass, 72 inch parallel maple lam, Handle, the 21.5 inch tapered maple lams (one on either side of handle) then finally, the 21.5 inch fiberglass pieces on top of the tapered maple lams.
The black fiberglass is covered with masking tape so these pieces look brown in the picture.
Here are the materials glued up on the form. I used the stretch clamp system for my glue up. Many people use bicycle tire tubing for this step, however I used 3/8 inch surgical latex tubing available at any hardware store. I used 4 feet of it on each side. The process I used for the glue up was as follows:
1. Place saran wrap on the bottom on the form
2. Put the epoxy in-between the bottom lams of maple and fiberglass that were just glued to the handle. (We till need to put glue both sides of the handle, remember!)
3. Spread epoxy on top surface of 72 inch fiberglass lam.
4. Spread epoxy on bottom surface of 21.5 inch tapered maple lam.
5. Put tapered maple lam onto the parallel maple lam making sure it runs up the side of the handle.
6. Put epoxy on top of 21.5 inch tapered maple lam.
7. Put epoxy on bottom of 21.5 inch fiberglass lam.
8. Place fiberglass lam onto tapered maple lam.
9. Repeat steps 2-7 for the other side.
10. Wrap saran wrap over top of bow so clamps don’t get glued to the bow.
11. Stretch rubber clamps over the form and laminations. I had just enough to go down and back twice.