--Photo by vivek
Once you have the space, equipment and necessary safety measures in place, the next step is to begin hollowing it out. Again, DON’T do this if you aren’t experienced with a chainsaw. It’s far too dangerous. In fact, I’m not going to write in too much detail to avoid tempting any inexperienced chainsaw users to try it out. I’m just going to offer precautions and tips. If you really want to hollow a base, make sure you are an experienced user, or have an expert by your side to mentor you.
Hollowing a base is particularly dangerous because you aren’t just slicing pieces. You’re sticking the chainsaw blade head-first into a solid piece of wood. There is an extremely dangerous, and very likely possibility of a kickback when you do this. A kickback occurs when the blade gets caught up in the wood, and results in the blade shooting upwards in the direction of your head. I shouldn’t have to explain why that’s bad. The need for a helmet is pretty obvious. There is a technique that is necessary to reduce the chance of a kickback. If you haven’t practiced doing this before, or if you don’t have someone with you who has, just don’t do it.
For those of you who know what you’re doing with a chainsaw, the first thing to do is to shave off the bark and any shallow rots. Leave more wood near the center, and take off more wood towards the ends to roughly achieve a barrel like shape. The flat ends of the log should look roughly circular. Keep in the mind the proportions that you calculated in the beginning, but leave plenty of extra wood at this point because we’ll be coming back to more fine-tune shaping in a later step (plus you want to leave room for error).
Next, using a leveling tool and a chainsaw, slice off the two ends of the log so that they are parallel to each other. In other words, if you stand up the log on one end, the other end should be perfectly parallel to the ground. The vertical sides of the log should be roughly perpendicular to the ground. Ideally, you want to slice down to the desired height of your eventual drum. However, I would leave 1-2cm of extra length on each side in case a mistake is made later.
You should now have two flat and parallel ends on the log. You now want to draw circles on each of these surfaces. These circles will represent the rim of your eventual drum. The part inside of the circle is the part you’ll be hollowing out. But this isn’t as easy as it sounds, because the circles on either end have to match each other. In other words, the center of the circle on one side has to be on the same vertical axis as the other. If this isn’t the case, you’ll be hollowing out a drum at a slant.
1. Mark the center of one of the surfaces. You can take some basic measurements to do this, or you can just do it by eye. It’s kind of arbitrary at this point but it’s OK. Using that mark as the center, draw two circles. One circle should be about 5cm bigger in radius than the other. The bigger circle represents the outer rim of the head, and the smaller circle is the inner rim. The space between the two circles is the wall of the drum. Everything outside of these two lines, you’ll eventually be shaving off or hollowing out. There should be a distance of at least 3-5cm between the bigger circle and the outer edge of the log.
2. The next step is to calculate the center on the other side. The next few steps are very confusing- I personally had a tough time with it. You might have to read it through a couple times over, but bear with me. First, place the log vertically on a piece of plywood. The side that you drew circles on should be at the top. Your goal is to draw a big circle on the plywood using the same center point as the smaller circles you drew on the top surface. The problem is, the plywood is on the ground, and the smaller circles are up above on the drum. See the problem?
You’re going to need some string, a weight, a flat stick and some thinking to figure out how to do this. Basically, you want to pivot the flat stick on the center mark on the top surface. From the end of the stick, dangle a string with a weight on the end of it. The weight should go straight down to the plywood below. Now, if you rotate the stick on its pivot, you’ll be forming the shape of a circle on the plywood below. Use a pencil or chalk to draw this circle onto the plywood.
You should now have a big circle drawn on the plywood. The center of this new circle is on the same axis as the one you marked earlier.
3. Don’t move the log yet! First, trace the outline of the log surface that is touching the plywood. Make some reference marks on the outline and the log itself, so that if you were to move the log off of the plywood, you can easily put it back on in the exact same position.
4. Move the log aside. On the plywood you should now one big circle, and a smaller outline of the log inside of it. Using a ruler or string, find the widest part of the circle. This is the diameter of the circle. Calculate the middle of the diameter, and voila, you’ve found the center of the circle.
5. You’re almost there! Let's go back to the reference marks that you drew on the plywood. Measure the distances between the reference marks and the new center that you found. Using these measurements, you should now be able to calculate the corresponding center on the second surface of the log. On this second surface, draw two circles as you did before (with the same radius), and you’ve done it!
Or not, if these instructions are as confusing to you as they are to me! Unfortunately, this is near impossible to describe with clarity in words. If I can find some photos, I’ll be sure to post them. But for now, if you read it over a couple times and use a model of a log (like a small cylindrical cut of wood) and actually try it out, you should be able to make some sense of it. If it still doesn’t make sense, post comments and I’ll try to answer it.
How to Make a Taiko Base (1. Choosing a Tree)
How to Make a Taiko Base (2. Equipment and Workspace)
How to Make a Taiko Base (3. Cuts and Measurements)
How to Make a Taiko Base (4. Chainsaw and Hollow)