Now it is time for the most important part of building a bow; the part where more bows bite the dust than at any other phase of construction. It is known as "tillering". Tillering is the cutting and scraping of the bow limbs to their final thickness and the balancing of the limbs so that they bend evenly when the bow is drawn. It's tricky, but if you follow a few basic rules and don't get in a hurry, you will end up with a good bow. Pictured below: Front profile of bow cut out.
You already have the back of your bow laid out and trimmed to shape. Now it is time to turn the bow on its side and draw in the side profile. For the plains style bows that I prefer to make, I do not draw in a distinct handle. I prefer to just make the handle area the thickest part of the bow (about 3/4" thick) and then taper down gradually into the limbs. You may wish to make a thicker and narrower handle. This is perfectly fine. It's just a matter of what suits you. It is usually best to use a ruler and measure the thickness of the handle first, then move to each end and make a mark to indicate the thickness of the tips (about 3/16" to 1/4" thick). Now you can go back and lay a straight edge from the mark at the end of the handle to the marks at the tip and draw in a straight line the tapers evenly from handle to tip. Please note that this will only work if your bow stave is perfectly straight, and they never are. You will probably have to draw in a very light straight line and then go back and make free hand corrections where the stave has slight bends in it. The idea is to keep the taper uniform. Any thin spots will bend too much and weaken the bow. I generally lay out my side profile on both sides of the bow due to the irregularities of any natural wood stave. Pictured below: Side profile laid out.
Now that you have the sides laid out, it is time to start removing wood. If you have a lot of wood to remove you can start with a hatchet, but be careful!! Keep turning the bow constantly and looking at both sides to make sure that you don't take off too much. When you start getting close to your lines, it's time to get out the ol' wood rasp. Work the limbs down carefully until you reach your lines. Pictured below: Side profile cut out.
At this point you will want to cut your nocks so that a string can be attached. I usually use a small rat-tail file for this and cut a nock on each side of each end. Some plains style bows have two nocks at the end where the string is permanently attached and only one nock at the end of the bow where the string slips on and off. Do it however you like. Pictured below: One style of nock.
If we lived in a perfect world you could now slip a string onto your bow and with the exception of a little sanding, it would be ready to shoot. But alas, the world ain't perfect, so rub a good coat of vegetable oil into your bow and let it soak in overnight before you string the bow for the first time.
When you do string the bow for the first time you want to be very gentle. Make sure that the bow is warm. Don't hold it over a fire or anything, just make sure that it isn't cold. Rub it briskly with your hand and flex it gently over your knee to loosen up the wood fibers a little. You will need to string the bow very carefully with a heavy string to prepare it for the final tillering, or balancing of the limbs. Don't pull the bow yet. Just string it so that there is about 5" distance between the handle and the string and then take a good long look at it.
Unless you are very lucky, one limb of the bow will probably be bending more than the other limb. In some cases it may be bending a lot more. The straighter of the two limbs is not bending as much because it is thicker than the limb that is more flexed. Obviously you can't add wood to the more bent of the limbs, so the only alternative is to remove wood from the limb that is thicker. Study the curve of the two limbs. Look at the straighter limb. Where does it need to bend a little more in order to look like the more flexed limb? Mark that spot with a pencil. I usually shade the whole width of the belly at the point that needs to have wood removed. Remember that the belly is the part that is facing you when you shoot the bow, and that this is the only side of the bow that we ever remove wood from. Picture below: Untillered bow. This one came out pretty close on the first stringing, but you can still see that the upper limb is not bending quiet as much as the lower limb.
Now take a sharp knife and, holding the blade perpendicular to the surface of the wood, begin scraping on your pencil mark. Scrape a fairly wide area. Don't dig a hole. When the pencil mark is gone, the limb will not have moved at all, but you must resist the urge to remove more wood. The actual results of your scraping will not become apparent until the bow has been drawn several times. Absolutely do not pull the bow back to full draw. Just flex it gently pulling the string back six or eight inches. Flex the bow at least ten times then stop and take a look at it. The straight limb should now be bent a little more, maybe not as much as it needs to be, but it is better. Now repeat the whole process; looking, marking, scraping, and flexing. Don't get in a hurry or you may wind up in the yo-yo syndrome. This is where you remove too much wood and now the limb
that was too straight is bent more than the limb that was too curved. So you have to work on the other limb and thin it down. If you're not careful you can end up with a bow that has a 10 lb. Draw weight. Pictured below: Laying the bow on a tile floor makes it easier to see where it is out of tiller.
Just take your time and do a lot of looking and a lot of flexing. As the bow approaches balance you can begin flexing it a little more with each pull, but you may want to stop and rub in a little more oil before pulling it too far. When you have the bow well tillered it is time to finish it out, which we will talk about in the next post. Pictured below: The bow is now tillered and ready to finish out.