--Photo by Alec Dy-Liacco
Now that the mind-boggling measurement step is over, you can finally hollow out the log. Again, don’t do this step unless you are experienced with chainsaws (please read why you shouldn't in the previous post).
Hollowing with a Chainsaw
Basically, in this step you’re hollowing out the circles that you drew on the two ends. The way I did it was to divide the circle into four parts (like a pizza pie in four slices), and cut out one section at a time. To cut out the sections, you want to insert your chainsaw blade directly into the wood and push it through as far as it goes. You want the blade to go in as straight as possible (you want to avoid cutting into the eventual walls of the drum). If you're log is longer than your chainsaw, then you'll have to insert the blade from the other side as well. If the incisions on the two sides match, you should be able to look into the cut and see through to the other side. Keep making cuts like these until you've cut out each section.
Again, I can't stress this enough, but inserting a chainsaw head-first into a piece of wood is very, very, dangerous. A kickback is almost inevitable, and almost any manual will tell you that this is exactly what you're not supposed to do. Please, please, please don't do this step unless you're well-trained with a chainsaw or have a chainsaw expert with you.
Other Hollowing Options
There are other options other than using a chainsaw to hollow it out. One is to use a heavy-duty power drill with a big bit to carve it out. This would take a little longer than a chainsaw, but it's far safer. Another option would be to look for a heavy-duty lathe. Places that work with large pieces of wood, like lumberyards and shipyards may have a heavy-duty lathe, or know of a place that does. You'll likely have to pay some money for them to do this for you, but it's probably the quickest way to hollow out a log. I would definitely try calling around to see if this is possible. Here's a Japanese website with a small pic of a lathe.
Finishing the Base
Once the log is hollowed out, you want to smooth out the inside surface of the drum. Using a chainsaw and/or an angle grinder, remove any bumps, splinters or crevices by evenly smoothing the entire inside surface. You’re going for a barrel-like shape, so the inside should also curve as it approaches the middle. (Note: Angle grinders are also dangerous tools. Study the manual careful and take all necessary safety measures. They also come in a variety of grinding discs, so find one that is made for grinding wood. A disc with a rougher grain is probably best for this step. Discs and grinders can be bought/rented at almost any hardware or DIY stores.)
Shave and smooth the outside as you did the inside. Shave it down to proportions that you calculated earlier. As a reminder, the widest part is about 1.15 times the diameter of the rim, and the wall thickness is about 5cm for an mid-sized nagado. You’ll need to go back and forth between the inside and outside of the drum in order to achieve an equivalent thickness throughout.
If you haven't made any significant mistakes up to this point, the rims of the drum should be parallel to each other and perfectly flat (as they were after the preliminary cuts). Use a leveling tool again to check that they are. If, however, a mistake was made at some point and there's a bit of a slant, you can still re-adjust the rims. If it's a big slant, then slice it off again with the chainsaw. If it's a smaller slant, you can use a jig-saw or a belt-sander to flatten it out.
When you’re happy with the shape of the drum, finish it using a belt-sander and sand-paper. Start off with a rougher grain of sand-paper, and gradually use finer ones as you finish off the sanding process.
You should now have a smoothly finished taiko base! I kept the explanations pretty simple here, so I'm sure there will be questions. Feel free to ask, I'll do my best to answer.
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)