The original PDF may or may not be easily available on Ocana's website. It is also hosted at: http://www.caseyconnor.org/images/cajon/cajon2.pdf. It contains vital images that are not shown in this text-only version.
Page 1
Amongst all the tasks floating around along with the everyday routines in my office, one that takes a lot of hours of my attention is to answer mails about how to place the strings in a cajón project, or how to make strings already placed in an instrument work better. I have always thought of this facet of cajón making as the most mediocre and sad one, as you have to face the straight-forward and cruel reality that this part gets too much attention and pampering in the consumer society. To the extent, that there is an increasing number of builders that concentrate on the strings only, and let professional woodworkers put together and varnish the cajon (Twice as sad in my opinion). The stringsetter has won the hearts, ears and purses of the people who are looking for this nice (and why not beautiful) timbre in a cajón, without paying attention to the very rewarding aspects that the owner of this workshop has made immortal in these days. Anyway, some make the big mistake of forgetting that they need a manual, guidance and a contact able to give advice, to rely on in their work.
Again, having a public workshop for years open for curious people, I'm the one who has been using my brain to help people and myself with this, I now hope that I won't have to answer so many mails in the future and can have a little more time off. I really hope this will not be seen as a reprimand, I do this gladly knowing that being generous makes me more professional and results in thankful people. Having said this, it's time to end the foreword.
Keeping the same pace as in education, we first start with understanding the basics, that is, the most known structure of a box, simply the back and front of it. We will not look at the daring models I bring to life, this manual will only cover the conventional cajón, with a rectangular structure consisting of the face, called the tapa, that we beat, and the back where the sound hole is.
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The methods we will study and that you will use are two of the most known and used by some of the most prestigious companies. It is possible that some of them may have patents, irregardless, these methods have been used for many centuries in other roles and activities, but in the modern world the person who registers a product is triumphant, not the one that creates it. So, to lessen problems we will recall that we are only providing information that will help understand the mechanism of these methods so that owner will know how to make the most of the product and solve problems with adjustment and repair. A very important detail, that can cause you to have no use of what you will learn here to regulate a cajón you bought at a store, is this:
The tapa does not need to be glued to the box, it should be screwed.
This is a very important factor when we subject ourselves to all of the various cajones available in a store. The sharp, bright sound of the strings deteriorates easily and you will need to take off the tapa sooner or later. As a buyer, there is another important factor to consider. Like we have seen in the previous pictures, the cajon is nothing more than a closed box with one of its parts (the tapa, the thinnest one) must move after being hit by all of the air in the cajon. The elegance of the resulting sound depends on how the parts of the cajon react to the hit. The moving air hits the internal faces of the cajon in waves, which should return to their place of origin with minimal degradation. The sound should not be absorbed by the material. This results in a sustainable tone with a agreeable equal oscillations. A cajon of high quality is made with a highly springy material, that, in the case of plywood and laminates, is of many layers. Try to find these cajones of many layered wood, observing the corners of the cajon is a good exercise, you will learn which ones lose less sound during the execution of a hit. Don't forget to also check the composition of the tapa; although it is thin it should be like a very strong paper that is able to vibrate with force and response.
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Ok, now, if you have made the mistake of acquiring a cajon that doesn't not respond well, can you make it better by solving these short comings? The answer is yes. However, not with miracle results, varnishing the inside of a cajón helps the air to return off the walls, and with better results you can impregnate the inside of the box with white glue (Elmers) that is lightly diluted in water. This will harden the material making it less penetrable.
These phenomenons of reflection also applies to the tapa. The sound wave that comes from the tapa is like a tidal wave and which bounce off the corners of the box. Another advice is to make sure that the sides are reinforced, this is good for the vibrations.
Picture of a cajon with a wooden frame reinforcing the walls.
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Where you play the cajon is important. Bricks and hard wood walls are the best for reflecting the sound back. Pine walls and plaster are not good.
Page 6
[I am going to translate the meaning from here out and not verbatim.]
Through the past various strings have been used, but acoustical an electric guitar strings work best. Then he just describes the strings of stringed instruments and how they are made. Nothing important.
[Ok, below the picture.] You can find strings with a flat core to them, but they are not suited for us. The best strings are 0.36 or 0.38 mm thick. Also, you don't have to know what note the strings would play in the guitar, but with the above numbers the shopkeeper should be able to provide you with the strings. Now we are going to learn the first method.
Page 7
We are going to locate 4 strings parallel to the tapa, at the part of it we would hit to get the higher tones. We will do this work in a box with out reinforcements on its corners. We will need 2 small blocks of wood about 6 x 2 x 2 cm, glue (with strong glue) the blocks the high interior wall of the cajon, like the following drawing shows. Below the picture: In these blocks we have already made the holes, 4 each, that will be used to thread the strings. Because the strings pass in front of the blocks, we do not locate the blocks flush with the front corner, but we leave a small space that is equal to the thickness of the strings that we will be using. If we don't do this, when we put the tapa on the strings will be deformed and their performance with be hindered.
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Note: It is common to find, even in famous brands of cajones, thread blocks made from strips of pine like you find in do it your self kits. Not only is this a wood that can't be drilled because it cracks, but it also changes due to the climate, heat and humidity. Sometimes warping part of the cajon where it is mounted. To find blocks that are more resilient and stable you can take advantage of the scraps of plywood left over from the cajon construction. Glue 2 pieces of 12 mm plywood together to get a 24 mm thick piece.
Picture shows blocks with string thickness gap.
Now we will prepare the screws that pass from outside the box to inside the box that will be used to tension the strings. One screw per string. The hole that we make in the box should be 1 mm smaller that the diameter of the screw so that it digs into the wood the first time we screw it in. Also we make a hole in the tip of the screw for the string to pass through. First with a small drill bit to go through, then with a larger one to open up the entrance and exit. As shown in the picture on page 9.
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Note: the wood of the box by itself will not be strong enough to hold the string tensioner in place. as the picture shows, reinforce the side of the box with another piece of plywood, or something harder if available. Use the same high strength glue what was used on the blocks.
Another note: Also, it is common to use staplers in the construction to facilitate and expedite build time. Most of the glues used currently in the construction of flamenco cajons are water based, like white carpentry glue. The glue stays viscous when it has water in it and when it dries the water leaves. By pressing the joints with clamps while the glue is drying, excess water is pressed out and a stronger, more solid joint will be. The staple is not recommended for pieces that must withstand tension.
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Now we can thread the strings. With this method one string can be used for two lengths of our cajon, you just have to tie a knot in one end of the string so that it does not pull through the hole in the block. Do not tension the strings too much before the tapa in is located because the cajon will be deformed.
Page 12
Our cajon is now ready to have the tapa put on. Tighten well the screws that secure it. We make our first test! You should go ahead and swallow in case the result is not what you were expecting. It never is. Plywood is not a perfect material, and although at a quick look it seems flat, it can suffer alterations that deform it. This can result in the strings no touching the inside face of the cajon. We can use a piece of adhesive tape or paper that will make the strings lay against the inside face of the tapa of the cajon. Of course, you will have to check and see if some of the strings are not tensioned now that the tapa is in place. They don't need much tension, just enough so that they are drawn into a straight line.
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Playing the cajon will result in the sound changing. Also, aging will effect the sound. Air conditioned or heated locations will dry out the wood. When this starts to be notable, the tapa turning concave or convex and the corners raising, you have reason to cure it. Plywood is made out of wood and glue, and can be steamed into shape. Press it hard with a steam iron, that will soften the glue and align the fibers of the wood. After that, you can dry the material for instance by an infrared heater.
Stringing in the shape of a "V", vertically from the top to the bottom, is a well known method among cajón players. The strings are twice as long as in the earlier method, and therefore it's a good idea to use thicker strings. A long thin string doesn't vibrate as much as a long thick one, so we will use strings of 0.42 to 0.52 mm thickness.
First, we will glue a bar into the top inside of the cajón that the strings will pass through, the fixed bar. Remember to allow the distance needed for the strings to vibrate freely, as explained above.
The second bar is smaller, and will be located at the bottom of the cajón. It is not glued, because it will act as a tension mechanism thanks to some screws that allows us to move it closer or more far from the bottom. It is called the free bar.
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[Pictures of the two bars attached to the top and bottom]
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[More pictures of the two bars attached to the top and bottom]
Making this bar is no harder than it looks. The screws rotate freely in the bottom of the cajón and grab the ends of the bar, in which we have drilled holes and put in threaded nuts made for wood. (In English, they are often called wood insert nuts or T-nuts, translator's note.)
[Photo of a screw with a nut on it]
These nuts fit precisely in the holes and stay fixed thanks to their wood grabbing teeth. You might also find other products at your hardware store, it's simply a matter of choosing something that will do the job.
[Photo of the free bar with two screws]
When screwing the free bar in place, we leave a gap of about 2 cm to the base. The appropriate way to thread the string is to start from the back of the fixed bar and then go to the front. You can then make the string loop down and up again in one piece if it is long enough, or make two separate strings. In either case you fix the ends with screws or nails.
[Drawing of a string threaded in one loop like explained]
You tighten the screws of the free bar both at the same time, so it will be pulled towards the bottom of the cajón maintaining its horizontal position and won't tighten one string more than the other.
With this simple lay-out, the strings will make more unwanted noise and interfere with the bass note, so taping them will not only bring them closer to the tapa, but also correct this imbalance. If you have enough space in your bars, you can turn your "V" system into a "W". (As the letter "W" can be drawn in many ways, think of a W where there are no crossing lines, translator's note.)
[Drawings of a V lay-out with tape]
Fine-tuning a cajón means adjusting the tension of the strings in a wise and balanced manner, so that the rattle of the strings won't dominate over the tone of your cajón, so the term "tuning" is a little misleading here. When the tapa is on, different factors affect the vibration of the strings, making them sound better or worse.
For instance:
The screws have to be tightened well. In plywood they don't have anything sturdy enough to grip into, so they tend to loosen. After the cajón has been played for a time, it's a good idea to tighten the screws, but remove all of them first, and put a toothpick dipped in glue in the holes. The toothpick will fill up the too wide hole and give a tight fit.
Another important thing is the number of screws in the bright sound region of the tapa. More screws result in less movement of the strings, and fewer in more movement. In any case, it's always better to have many screws, because this gives a better low note, and to get more of the bright sound you can loosen the screws at the tops of the vertical rows.
[Drawings of a tapa vibrating. Fewer screws at the upper region - more vibrations. More screws - less vibrations]
Well, this ends this humble writing aimed at the "surfing cajón builder". I didn't write this to make anyone jealous of my knowledge. Anyone with two hands, not hindered by the passiveness that comes from the today's excess of information, would have come to the same conclusions. I hope this manual will aid current and future flamenco cajón owners, and that percussionists would restring their cajónes, just as guitarists change strings on their guitars, to get their own, personal sound.
Germán Ocaña