A pump-drill with too many revolutions during its cycle will run out of momentum on the rewind and not be able to tolerate much downward resistance. As we have already discussed downward resistance on the upward travel of the crosspiece is essential for maximum efficiency. Without downward resistance the drill will actually be coasting, waiting for its next power stroke. It will lack power, operate slower, and feel as if it can't keep up with you.
An ideal number of revolutions per cycle is somewhere between three and four. This will allow you to achieve a crisp, responsive drill as it is under more constant power by you. You will have sufficient time to develop maximum speed and momentum.
To adjust the revolutions per cycle on your pump-drill, wind up the crosspiece and slowly push down on it, counting the revolutions until the crosspiece reaches the bottom. It should be between 1 1/2-2 revolutions as this is only one half of a cycle. Adjust your string accordingly.
You will notice that I have been referring to string length and not spindle length. The spindle can be as long as you like as it is only the working area of the spindle that is important. That area is determined for the most part by the strings length. The spindle length only becomes a factor if you don't have sufficient length to adjust your string to the proper revolutions per cycle.
Photo 16. Abrading the rough edges.
Photo 17. Burn-drilling the holes.
Photo 18. Notching the ends of the lower pieces with a sharp rock.
Photo 19. Testing the finished, tuned drill. I got a coal in 19 seconds.
Step Two - Selecting the Flywheel Weight
The main criteria for selecting the flywheel weight is the amount of pressure you need. For drilling holes, you want to select a weight that allows for the application of sufficient pressure on the downward and upward phases to allow the bit to cut or abrade its way through the object being drilled.Too little pressure and the bit will not engage but spin idly. Too much pressure and the bit will punch or crush its way through doing little cutting. Smaller bits may even tend to shatter. For firemaking, you should have sufficient pressure to generate dark brown dust that flows freely from the notch. Too little pressure and there will be little or no dust or it will be too light in color. Too much pressure and the tip will tear apart or deform.
With this criteria in mind, test your pump-drill using different weights to determine if you are generating sufficient pressure. Starting with a 1 1/2 lb. flywheel, test your drill. Then increase the weight by 1/2 lb. and compare how each weight increase in the flywheel relates to its performance. As you get closer to your optimum weight you should increase the weight in smaller increments.
Ideally, it is nice to have an assortment of different weights to experiment with but almost any stones will do. Remember, you can make up for differences in size with buckskin or cordage. For small increases in weight, you can lash sticks along the crosspiece. Once you settle on the ideal weight, you can later replace them with nicely shaped stones of equal weight.
For our example, I found that a weight much below 1 1/2 pounds did not allow for the application of sufficient pressure to generate the color or volume of dust critical to firemaking. As I increased the weight, performance started to pick up until I reached 2 3/4 pounds. As I increased from there I started to experience more and more bit deformation and at 4 pounds had a lot of bit failure. I had a usable range between 2 pounds and 3 1/2 pounds with the ideal setting approximately 2 3/4 pounds.
Step Three - Determining the Crosspiece Length
The last factor we need to adjust is the amount of torque available as the crosspiece moves downward. The torque available on the downward phase (from here on referred to as downward torque) should match the torque the flywheel generates on the upward or rewind phase. By balancing these two forces the drill will take on a more consistent speed. Neither phase will overpower the other and the drill will operate more smoothly and fluidly.
The downward torque is a product of string angles. The more outward (closer to 90 degrees measured from the spindle) the pull of the string away from the spindle, the more downward torque the drill will have. The factor which we will be using to regulate the string angles is the length of the crosspiece. The longer the crosspiece the closer to 90 degrees the string angles will be and the more downward torque the drill will have.
We intentionally overbuilt the crosspiece in length and attached the string to the very end providing a high level of downward torque. This allowed us to select the ideal flywheel weight as a drill with insufficient torque is more limiting in its ability to handle weight. With the weight selected we now need to reposition the string on the crosspiece to the location which best balances the torque on upward and downward phases. Each time you move the string it impacts the revolutions per cycle. Therefore, you must also readjust the string length to return the revolutions per cycle to their original setting. This will ensure that you are only comparing differences in crosspiece length without any other factors influencing your comparison.
To find the ideal length move the string inward on the crosspiece in two inch increments (remember to readjust the revolutions per cycle each time). Test your drill at each interval and continue until you reach the point where the drills performance starts to drop off. At this point move the string back outward two inches, readjust the revolutions per cycle and your drill is tuned.
For our example drill, I tested each interval for about 20 seconds noting its performance. When I reached the 21 inch length the drill seemed sluggish and less responsive and it required more effort on my part to reach the same level of speed and power as before. In short the drill's performance dropped off. To complete the tuning I repositioned the string at 23 inches and readjusted the revolutions per cycle.
Keep in mind that there is a range if acceptable performance for every pump-drill and somewhere in that range is an optimum setting. The guidelines in this article will get you into that acceptable range. The optimum setting may vary from person to person and from drilling job to drilling job. You may want to increase or decrease the weight, revolutions per cycle or crosspiece length slightly to make any final fine tuning adjustments, personalizing the drills performance. Once you are satisfied with your final adjustments, you can cut off any extra length of crosspiece and/or spindle and go back over the drill cleaning up and reshaping any rough surfaces.
In testing the example drill, I was able to get a coal in under 20 seconds. From tree to completed pump-drill took under three hours using only stone tools. Using a softer wood for the crosspieces and a notch instead of a collet chuck could cut construction time down even further. Following is a breakdown of the time of construction:
Chop out section and split out crosspiece - 25 min. Shape spindle, notch and make chuck - 40 min. Abrade crosspiece, burn-drill holes, notch
crosspiece ends - 20 min.
TOTAL 175 minutes
(2 hours 55 minutes)
So, there you have it, an efficient, durable pump-drill that can be constructed in under three hours using only stone tools. Remember, this pump-drill does not require any searching for a special shape or certain type of raw material as any straight section of wood will do. The weight can be almost anything, even sections of wood from the same tree the pump-drill was cut from. The adjustability of the flywheel makes this a truly versatile design.
For those individuals who are not interested in fine tuning but want an efficient pump-drill for firemaking, simply use the following dimensions:
Fire tip 5/8 - 3/4 inches in diameter
Crosspiece 22 - 24 inches in length
Weight 2 1/2-3 pounds
String length 31 - 35 inches in length
What I have demonstrated is my approach to designing and tuning a pump-drill. It is not the only way, but I feel it is an effective one. As your experience and knowledge grows, you won't need to overbuild or adjust your drill to the degree we did in this article as you will know how to target closer to the final dimensions.
There
are a few variables that I did not cover. Their impact on good pump-drill performance is not as significant as the variables we discussed and their inclusion would make tuning much more complex. It is beyond the scope of this article to cover these variables, but perhaps a future article can, along with discussing some additional pump-drill modifications. For those interested in doing some additional experimentation, these variables include:
1. Spindle diameter and shape 3. String stretch
2. String diameter 4. Weight placement
Finished pump-drill parts disassembled.
All in all, a properly designed and tuned pump-drill is a pleasure to use. Its consistent performance is great for testing different stone bits for drilling efficiency, the effectiveness of different fireboard notch shapes, the combustion time of woods, etc. It is a great camp tool, and the mechanical advantage it offers makes firemaking and drilling easy and fun for anyone. Happy drilling.
A NOTE ON TINDER BUNDLE CONSTRUCTION
Text and Photos By Charles Worsham
* * *
One of the most exasperating things in friction firemaking is to spin out a coal and then not be able to light the tinder bundle. Perhaps the tinder was a little too damp, or maybe the coal was too small to generate enough heat, or possibly the fire-maker blew too hard: cooling the coal and adding unnecessary moisture. Feeling the need to hurry the process is also a preamble to failure, as is not giving due consideration to what constitutes a properly made tinder bundle. Indeed, there is one aspect of tinder bundle construction which is often overlooked—the COAL EXTENDER.
The coal extender is one of several different ingredients which, when added to the core of the tinder bundle, will eliminate most or all of the problems listed above. It will extend the life of the coal; it will enlarge the size of the coal; and it will allow more time for the fire-maker to carefully nurse and coax the tinder bundle to flame. Moreover, a coal extender, by increasing the life of the coal, will allow more time for residual moisture to dissipate from the bundle. Additionally, the increase in coal size and coal longevity will result in raising the core temperature of the bundle more rapidly and more substantially. And all of this can be achieved with little or no blowing on the tinder bundle.
Figure 1 - Coal extender materials.
In general, a coal extender will not break into flames itself. However, it will smolder and glow like a coal and will generate very hot temperatures which will aid in igniting the surrounding tinder material. Some of the better coal extending materials are illustrated in Figure 1 and they are as follows: 1) cracked-cap polypore (lower left and lower center); 2) rotted wood (upper left and lower center); 3) duff (lower right); 4)oak apple gall (upper right).
CRACKED-CAP POLYPORE
The cracked-cap polypore (Phellinus rimosus) is a member of the Polyporacae family whose numerous species are noted for their use in various primitive skills. Some are choice edibles; others have medicinal value; a few can be used as dyes; and still others have importance as tinder materials. Mors Kochanski in his book, Northern Bushcraft, discusses some of the uses of these polypores (pp 16 & 29). The cracked-cap polypore is found almost exclusively on living or dead black locust trees (Robina pseudoacacia). Black locust originally was native only to the Appalachian Mountains from Pennsylvania to Alabama, and part of Arkansas, eastern Oklahoma and southern Missouri but now has been planted successfully in most states. Black locust cannot tolerate shade and will begin to die out when other hardwoods compete successfully for sunlight. Where black locusts are stressed and dying, the cracked-cap polypore is most likely to appear. In areas where black locust is scarce, other species of trees may supply additional kinds of polypores which will work well too. The cracked-cap polypore is an excellent coal extender, requiring no drying time before use and working well under any weather conditions. One small cracked-cap polypore will supply enough material for years of fire-making. Simply shave off a little pile of slivers (Figure 2) and place it in the center of a pre-constructed tinder bundle. Make a slight depression in the center of the polypore slivers and add the smoldering coal. The important thing at this point is to make certain that the coal is touching as many of the polypore slivers as possible. Each sliver, in turn, will begin to smolder and glow. Coal size will expand to include all of the polypore: heat will begin to rise more rapidly and the odds of producing a flaming tinder bundle will increase tremendously.
ROTTED WOOD
Next to the cracked-cap polypore, rotted wood can make an excellent coal extender. Most tree species are a source for tinder core material especially hollow, dead, or dying trees. Rotted wood, therefore, is much more available than cracked-cap polypore, but it has the disadvantage of not working well when wet or damp. A few dry pieces crumbled up in the center of a tinder bundle is all that is needed to enhance the quality of a coal and ensure success in creating flames. The first two examples illustrated in Figure 1 (upper left) are from southern red oak (Quercus falcata) and the third is wild cherry (Prunus serotina). The samples from red oak show two different forms of rotted wood. The first was taken from inside a large hollow tree and has the appearance of sawdust. When rotted wood has reached this state, it does not enhance a coal as well as more solid slivers of punky wood. However, by wetting this sawdust form and compressing it into a more solid ball, it will work almost as well as the more firm pieces of wood. Just put it somewhere to dry out, then break it up into little chunks and place in the tinder bundle. The second example of southern red oak and the piece of wild cherry illustrate the best type of rotted wood, punky but not too soft and solid but not too hard. It can be broken up in to slivers, all of which will turn into individual glowing coals when brought into contact with the primary coal.
DUFF
When the word duff is mentioned, it usually elicits a dumbfounded expression followed by the word, "huh?" Duff (Figure 1 lower right) is the partly decayed organic matter on the forest floor. A forest fire which burns into the duff layer is a firefighter's nightmare; it is almost impossible to extinguish. A fire in this material can smolder unnoticed for days burrowing under fire lines and springing back to life with a vengeance. A duff layer fire is usually the product of long dry spells and, like rotted wood, it does not burn well when damp. Duff is hard to describe; it looks like dirt, but dirt will not burn. It is usually found on south facing slopes and seems to occur around oak trees. Duff tends to be grayish in color and, when lifted from the ground, it usually pulls up like little pieces of carpet. As a coal extender, duff generates incredible amounts of heat and will smolder for extended periods of time.
OAK APPLE GALL - The oak apple gall (Figure 1 upper left) is a growth which occurs on oak trees and is the repository for the eggs of the oak apple gall wasp (Amphibolips confluentus). The gall grows as a chemical reaction to the wasp's sting, and the dry, spongy substance within the papery shell can be used as a tinder bundle core. However, the oak apple gall is listed here with some reservation; it is clearly not as good a coal extender as those listed above. It does not seem to generate as much heat, and its fire-making properties appear to decline as it is exposed to the elements over the winter; best results occur in the fall. Even so, this growth has possibilities and is worth experimentation. Crack open and remove half the outer shell of the gall. Take out the spongy core and compress tightly. Then add the compressed centers from several other galls and place all of them back into the half shell and it is ready for use. Put the half shell with the compressed centers into a tinder bundle and drop the coal into the oak gall shell. The spongy core will smolder and the papery shell will reflect heat back to the center of the gall. It is important here to make certain that tinder material is making contact with the inside of the gall, otherwise it will not catch fire. One of the advantages of the oak gall is that the papery shell will keep the inner material dry during wet weather (up to a point). In extremely wet weather, however, the spongy core will become damp and will be totally useless for fire-making until thoroughly dry again.
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br /> Figure 2 - Cracked-cap polypore shavings.
If the tinder bundle is carefully and properly constructed to begin with, and a good coal extender is added, no blowing on the bundle will be necessary. Simply add the coal, close the bundle up (not too tightly), and walk away; in a while the tinder bundle will erupt in flame without any further coaxing. Putting it another way, this means that the fire-maker can put a coal into tinder, place the bundle within the kindling tipi, go get a drink of water, make a phone call, address a few Christmas cards, and return just in time to see the tinder bundle catch fire and ignite the kindling. In terms of clock time, a tinder bundle made of red cedar inner bark with a cracked-cap polypore coal extender can easily sit unattended for over twelve minutes before catching fire by itself (see Figures. 3 & 4). Now of course there are a number of factors which will reduce the chances of getting tinder to flame by itself: too wet; too much air; too little air; poor choice of material; too humid; too cold, etc. However, even when these factors make ignition difficult, a good coal extender can improve the tinder bundle to the point where a slight puff of breath or a gentle waving of the bundle is all that will be needed for success. Experimentation with various tinder materials and coal extenders will soon produce a list of those ingredients and combinations which will most often catch fire with little or no work after the coal has been inserted.
For a survival fire, the coal extender can give the fire-maker a larger, hotter coal, more time for drying damp tinder, and more of a chance for success under adverse conditions. For a ceremonial fire, the coal extender can give the fire-maker all of the above plus more time to patiently create a fire which can be a work of art. Graceful movement, an unhurried pace, carefully assembled equipment, and visually exciting moments from beginning to end are important aspects of a ceremonial or spiritual fire—the coal extender can help it happen.
Primitive Technology Page 10