You may remember some time ago that I posted the first in a series of posts which talk about how I make these wonderful instruments, where I talked about shaping the flute. Today I’m going to show you something of how to make the basic body of the flute – which is actually one of the most challenging aspects of the job.
Take a look at this diagram which shows the inside construction of the flute; the dotted line down the centre shows where the two halves of the flute are joined. These two halves have to be made separately and glued together, before shaping the body to look like a flute.
This post is about what has to be done to make the body of the flute – and some of the things you have to think about. First of all you have to decide what key range you want the flute to play in: each size of bore will fit into a particular range of keys. The most common bore, about 3/4″ or 19mm, will generally make flutes from about F4 (F above middle C) up to about B4… you can make workable flutes just outside these ranges but it starts to cause difficulties and a need for far more accuracy than is reasonable. Once you’ve decided the bore size, you need to select a piece of wood which is big enough (width and depth) to accomodate the bore and leave enough wood to make the shape; too small and you’ll have a squarish shape at the end – too small and you’ll have a lot more shaping work to do. Also, the length needs to be enough to accomodate both chambers, the ramp, the flue and the mouthpiece.
Now, you need to mark up. This is more vital to get right than the actual cutting of wood; mark twice and cut once as the old saying goes. You need to mark lines all the way around both halves of the flute for the top and bottom of the slow air chamber, and the top of the bore. I often make the front half of the slow air chamber a bit longer than the back half; this makes cutting the ramp easier. Next you need to mark on the front of the flute where the ramp and the flue will go, as well as the true sound hole and fipple (cutting edge).
Once this is marked, I use a router (MUCH quicker than cutting out by hand) to cut two channels in each half – the short channel for the slow air chamber and the longer for the bore. You need a router bit which is called a “Core box” – it has a dome-shaped head and makes a cut with a half-moon shaped cross-section. You’ll need to do several passes at steadily increasing depth until the two halves make a perfectly circular cross-section. Take your time; get this right. If you cut slightly too deep, use a plane to carefully bring the depth back down. (A thicknesser is a useful power tool here).
This done, you need a chisel of the right width to cut your ramp – a short ramp in the back half at the bottom of the slow air chamber, and the rest of the ramp needs to be carefully cut from the front and back of the front half until it meets in the middle. Again – this is critical so take care and time. The flue is cut with a micro-router set to the critical depth. The true sound hole is next; the sharp edge needs to be at half the depth of the flue. You can use many techniques; I use extreme care and a chisel – the top-to-bottom dimension of this rectangular hole should be only 2-4mm; the width the same as that of the flue. With the right type and size of cutter, a micro-router can be used for this but it’s no quicker and if anything even more care is needed due to the high rotational speed of the tool.
Once all this is done, you’ll have something like the picture on the left. Once you get to this stage, all the airways need a coating of oil so that moisture doesn’t enter the wood… once this oil has dried you coat one half’s mating surfaces with an even covering of top quality wood glue, mate them up exactly (so that the blowhole and bore don’t have lips inside) and clamp. I leave it clamped for 24 hours before doing any further work.
With practice, this stage can be completed in a day but I wouldn’t try to go fast here; just make sure each step is done properly.
While it’s clamped up, you can make a block for your flute so that when you unclamp you can play it’s first note and cut it to length for tuning… but that’s another story 🙂