Notch Construction: Secrets of the Bow Drill

friction fire by bow drill

In real estate, they say there are only three important factors; location, location, and location. When making fire by friction, there are also three important factors; materials (type), materials (condition), and materials (preparation). As a child, I once used my dad’s electric drill to make fire by friction with a pine dowel rod and a pine “fireboard”. Without any knowledge, or even a notch to catch the coal, the trial was, of course, doomed to failure. The wisdom of maturity has shown us that pine is one of the worst materials to use for a fire drill. And that the notch is a critically important feature of the fireboard.

Many authors have described the selection of natural materials. In this article, I assume the reader is acquainted with the general technique of firemaking with a hand drill or bow drill. I will focus on material preparation, a topic that is seldom considered in sufficient detail. In particular, I have found that descriptions of the fireboard notch tend to be over-simplistic, with wide variations in style. Yet I believe that notch construction is a crucial factor in converting muscle energy into a glowing coal.

To be most efficient, you must shape the notch so that it holds together the dust ground from the spindle and fireboard, yet allows easy removal of the fireboard without disturbing the coal. The size of the notch must also be in proportion to the diameter of the spindle and the thickness of the fireboard. Finally, it should be easy to make using only a sharp-edged stone tool. I describe below a system that consistently meets these goals with minimum effort.

Let us consider the topic of proportion in general. Spindles for hand drills are usually longer and thinner than spindles for bow drills. Fireboards are typically proportional to the spindles, so hand drill fireboards are thinner and narrower. One way to easily remember dimensions is to use your hands rather than memorize measurements that require a ruler. For example, a convenient size for a hand drill spindle is the diameter of your little finger and length from outstretched fingertips to elbow. If the spindle material is hollow, cut the end off flat. If the spindle is solid, make a blunt point. The fireboard thickness should be from one half to two thirds the diameter of the spindle. Its width should be about twice the diameter of the spindle. The fireboard may be any convenient length. A common size for bow drill spindles is the diameter of your thumb and the length from the tips of your fingers to the base of the palm. However, it is quite possible to make a bow drill spindle if you can only find smaller material. You can make a working spindle from a piece the diameter and length of your little finger if necessary (with a proportionately small bow). Bow drill spindles are usually solid, rather than hollow. The end that joins the fireboard should be a blunt point and the end that goes into the hand hold should be a sharper point. For the fireboard, use the same rules of thumb as for the hand drill.

I have seen fires come out of the worst materials with the crudest and most misshapen notches you can imagine. So it is hard to argue that notch geometry is critical. But it makes sense that the more precision you put into material preparation, the more efficient the fire making tool becomes, and the more success you will have with marginal materials or experience level.

With the drill and fireboard properly sized, you are ready to construct the notch:

  1. Start by placing the prepared drill end at the edge of the fireboard somewhere along its length, usually near one end. Place a mark on the other side of the drill so that the mark is one drill diameter from the edge. This mark will be the center of the hole made by the spindle as it burns into the fireboard. Note that the edge you are measuring from is whittled so the top, bottom, and side are at right angles, like a little piece of lumber.
  2. Press the spindle into the board to make an impression centered on the mark from step 1 (the fireboard wood should be soft enough to indent when pressed with your fingernail). Use your knife to dig a shallow indentation. If the spindle is solid, the indentation should be cone-shaped. If it is hollow, make the indentation disk-shaped (just deep enough to keep the spindle from slipping out during the next step).
  3. Place the drill in the impression and twirl to create the initial burn hole. If the spindle is hollow, the hole will be a ring. Burn in just enough to make a small depression the same diameter as the spindle.
  4. With your knife, scribe three parallel lines from the top of the fireboard to the bottom. One just touches one side of the burn hole, one goes through the middle of it, and the third touches the other side.
  5. Use your knife blade to measure the distance from the edge of the board to the first mark you made (in Step 1). Turn the board over and place a mark this distance from the edge along the center line. This mark is now under the center of the burn hole. Let’s call this point X.
  6. Scribe two lines from point A to the intersection of the outside lines and the bottom edge of the board (points Y and Z).
  7. From Y and Z, scribe up the side of the board to the top of the board and on to the middle line. These last two lines should intersect the middle line about one quarter the distance from the edge of the burn hole to its center.
  8. With your knife, chop out a small wedge of wood from the bottom edge of the board into the center of the diamond (just two straight v-cuts along the middle line). Make the wedge bigger until it expands to a diamond-shaped notch. The apex of the notch (on the top of the fireboard) should just break into the ring of the burn hole if you are using a hollow stem drill. The apex should extend about halfway to the center of the burn ring if using a solid core drill. You will now have a notch that flares down and out as described in some books but scaled precisely for your materials. Make sure that the final notch has smooth edges and surfaces. Any rough spots will cause gaps in the dust as the spindle burns into the fireboard. Air pockets insulate parts of the pile and retard heat buildup so that a coal may not form. Attention to detail during initial preparation may avoid your having to do it again.

Your fireboard is now ready to receive the spindle and make a coal. As the spindle rotates and burns into the fireboard, the notch will widen just enough to catch the resulting dust, compact it, and concentrate the heat. At the same time, the outward flare to the notch allows oxygen to get to the coal so that it can grow. You should be able to get at least two fires from one hole. If you are using a hollow material for a spindle, a plug of wood will form in the center of the burn hole. Before attempting the second fire, shave off the plug level with the bottom of the burn ring. This reduces unnecessary friction and binding.

The first time you try these steps, it might seem complicated. However, after just one successful outcome you will see that the procedure is quite natural and intuitive. The main advantage is that the notch is automatically scaled to the size of your particular drill and fireboard thickness. This makes your set more efficient and more likely to start a fire, even when material or environmental conditions are poor. The inverted hole created by this type of notch may have an advantage over the more conventional parallel-sided notch. This type of hole seems to keep the dust together and concentrate the heat better.

Another theoretical benefit of this type of notch may derive from the way it changes shape as it is being used. You will observe that as the drill digs down into the fireboard, the pie-shaped notch visible from the top of the fireboard widens due to the fact that the notch fans out toward the ground. This means that the pressure between the drill and the fireboard increases as you drill, because pressure equals force (ie, downward force on the drill) per unit area (ie, the area within the burn hole). The increasing pressure and decreasing area may serve to concentrate the heat of friction more (increasing your chances of getting a coal) than what you would get with a standard notch, whose area within the burn hole remains constant.

There is at least one more advantage of this notch design. Under primitive conditions, you may not have a knife or any good rock material to improvise one. However, the diamond shape of the notch allows it to be filed rather than cut. This means that all you need is a thin sandstone pebble broken in half to make a filing surface along the break edge.

One last tip: There are two ways to get the coal from the fireboard to the tinder bundle. One way is to catch the coal on a thin piece of wood placed under the notch and then transfer the coal to the tinder. The obvious problem with this is that you may drop the coal on the way to the tinder bundle. The other way is to place the tinder bundle under the notch so that once the coal is created, you simply remove the fire board and blow on the tinder. The practical problem with this is the tendency for the tinder fibers to get caught in the rotating spindle. Another problem is that the tinder may wick moisture from the ground. A simple remedy for both these problems, is to make a tinder bundle “sandwich” by placing the tinder fibers between two large, very dry leaves. The bottom leaf protects the tinder from the ground and the top leaf keep the fibers out of the notch. The coal easily burns through the top leaf and into the tinder.

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