Building a bow with some set-back in the handle is an effective way to keep string follow at a minimum. It is a rule of thumb that when comparing two identical staves — one with set-back in the handle and the other perfectly straight — the bow made from the stave with the set-back in the handle is always going to have less string follow.
In Volume I, Tim Baker explained that the level of string follow shown by a bow is — on average — the greatest single indicator of how efficient the wooden bow will be. My own performance tests — described in The Bent Stick — support this premise 100 percent. If you want good cast per pound, keep string follow to a minimum.
When a new bow has some set-back in the handle, the limb tips are farther forward than a perfectly straight new bow. And this makes it easier to keep string follow low.
There are other factors in keeping string follow to a minimum. They include: good bow design (such as making the limbs wide enough, and keeping the belly as flat as possible), good tillering and workmanship, and not subjecting the bow to excessive strain during the construction process.
How much set-back is enough? Lay the bow stave on the floor, belly up. Measure the distance from the back of handle to the floor. In theory, the set-back can measure anywhere from 1/4 of an inch to about six inches or so. But six inches is more dangerous than three inches. And three inches is more dangerous than 11/2 inches. Severe set-back places more strain on the back of the bow. A stave with six inches of setback can make a bow, but the tillering must be absolutely flawless. If one section of the limb is overstrained a tiny bit, that section of limb can easily break.
It is much safer to keep set-back at reasonable levels. I think 11/2 inches is a good rule of thumb that will produce the desired results under a broad range of circumstances.
One of the best methods ever described for steaming set-back is also one of the oldest. It is described in the 1936 book The Flat Bow, written by W. Ben Hunt and John Metz. Hunt and Metz describe steaming six-foot staves that were about 2 or 2 1/2 inches square. The stave was steamed for at least an hour, then quickly put into a press and tightened with either a vise or two nine-inch clamps. The wood was bent so each limb tip moved three inches from a straight line. The wood was left in this position until it cooled.
Even though the limb tips were moved three inches, they would tend to move toward their original position when removed from the press. So the final setback would be about 2 or 2 1/2 inches. These distances are well within reason for a six-foot bow.
Remember what you just read: A piece of wood can move back toward its original position after it is heated or steamed and bent. When steaming a crooked piece sideways, it is a good plan to bend it slightly past the straight position. Then the piece will be straight when cool.
It should be mentioned that a finished bow can sometimes be improved by steaming set-back into the handle. This can increase draw weight, decrease string follow, and improve arrow speed.
I once had a yew stave that had a natural deflex of about two inches. Since any yew is valuable in my area, I made a bow from the wood. This was an English style bow that worked slightly in the handle. It followed the string about three inches. I was frustrated because the bow was a mediocre performer, and so decided to steam a reflex into the handle and see what happened. I steamed the bow and clamped it into a press so the limb tips were in a straight line with the handle. Ultimately, the string follow fell to about two inches. The bow gained about three pounds in draw weight. Performance improved significantly. I was a happy camper.
THE LIMB TIPS
There are two kinds of recurves which can be put into the ends of a wooden bow.
The first type is the static recurve. The bow limb itself bends, but the static recurve does not. It keeps its basic shape throughout the draw. The second type is the working recurve. The working recurve does bend as the bow is drawn.
There are two ways to make a working recurve. One way is to steam a slight reflexed "kink" about three to six inches from the limb tip. The bow is tillered so this kinked spot flattens slightly as the bow is drawn. This method is not too difficult to accomplish.
The second way is to make the recurve rounded, similar to a glass-laminated recurve. This must be done carefully for best results. If the wood of the recurve is too thin, the recurve can be pulled out by bending the bow. Perhaps worse, the recurve can warp sideways. This is caused by the weakening of the wood cells described earlier. If the recurve warps sideways, it can be impossible to keep the bow strung. It is just plain difficult to make such a working recurve wooden bow. Static recurves can also have an angular or curved appearance. But with a static recurve, the wood is thick enough not to bend.
In the 1930s and 1940s, it was not uncommon for even static recurves to be pulled straight by the strain of shooting. For this reason, bowyers often laminated extra wood on the belly side, to keep the recurves froirt losing their shape.
If a recurve is bent only slightly, it can be done handily with dry heat. If any recurve is to be bent severely, steaming and boiling are usually safer methods.
It is possible to repair a bow's tiller by recurving only one limb tip. Let's say we have a good flatbow, but the lower limb bends too much. Using dry heat or steam, you can warm up the lower limb tip and bend a slight kink into it about two inches or so from the tip. Let the wood cool thoroughly and string the bow. Draw it a few times. You can expect the lower limb to bend less and the upper limb to bend more.
World History
