Conical bamboo flute making: my latest failed attempt

World/Folk Flutes & Winds
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Here’s my latest failed attempt at making a conical bamboo flute with 2 decent octaves.

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This one, in key of E4, is a failed attempt because the top 3 notes of the 2nd register, though playable, still go flat despite the taper.

I suspect this is because of the taper being insufficient. This one starts at 29mm on the head and ends with around 24mm OD at the foot. Wall size is 3mm for the record.

I suspect if it were around 23mm at the foot it would solve the intonation issues. Or if it had a slight widening around 7cm after the embouchure.

For the next iteration I should also move up the R2 tonehole to make it smaller since it’s a little big at 12mm.

Nonetheless, this was enjoyable. On to the next ones.

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Good on you, sagadabeans. But I think you are right, not a fast enough taper.

Typically a conical flute like we use in Irish music will have head around 19mm bore, a body that starts around 19mm and tapers down to around 13mm, followed by a foot that continues downward if low keys are added, or might flare if not.

Your suggested diameters for a slightly higher pitched flute sound a bit high, compared to the figures above.

Now it seems to me it’s unlikely to be able to find cane that tapers anywhere near fast enough to simulate our body tapers. Boehm’s approach might be more achievable. His head went from about 17mm to 19mm, then the rest of the body was cylindrical at 19mm. But even that head taper sounds hard to realise.

At this point, I wonder what happen if you combined the two approaches? Cut the cane and reverse it for the head so it is tapering upward as per Boehm. Join it to the wide end of a piece tapering downward for the body. Add on a bit reversed for the foot.

Not sure how you’d make the joints. Heh heh, not my problem! But incorporating a tuning slide between head and body would be good!

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Thanks Terry. I’ll try a smaller bore in the next iteration and see what happens.

The Boehm approach does make sense. Perhaps I can find a particular geometry for a bamboo stalk that mimics the Boehm taper at the head so that the rest of the body can just be cylindrical. Since I harvest the bamboo myself it can be an interesting challenge to find the right ones.

That seems more feasible for me at the moment since I don’t have a lathe yet and lack the skills to make tuning slides (but something to look forward to in the future).

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How did you go about measuring the taper along the inner bore? If you are only measuring at the ends then it’s possible that you are being misled. I have a LOT of experience with this!

I make bamboo flutes of various kinds (when I can find the time) and I’ve messed about with selecting species that have enough natural taper to allow for a semi-Boehm style taper at the head, but it is very rare to find any that have a meaningful taper running their length that is sufficient to make a “conical” bore. Plus, it is quite normal to have some slight constriction near the nodes, making it difficult (more like impossible) actually measure the bore diameters along the length of the stalk. Also, it is normal to find bamboo that narrows along the length of the stalk, but on the inside it more resembles a step-bore than a taper. So at the fat end you have what is basically a cylinder in between the two nodes. As you travel along the stalk (going from fat to more narrow) you have another cylinder between the nodes, but it might be a hair narrower than the first. Likewise for the next section. Here is a very crude sketch that is a bit exaggerated to illustrate what I mean (hard to draw with a mouse).

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Lots of bamboo present this way, and you will not get a genuine taper without serious bore manipulation. You can sand out the inner nodes pretty aggressively to try to give access with measuring tools, but short of some type of high-tech laser measuring device you can’t get a proper survey of a bamboo bore. I usually profile a bore using t-gauges, but that won’t work, at least not well. Not only is the bore organic and irregular, but the slight constriction of the nodes means that you might get a t-gauge inserted to the point you want to measure, but you can’t get it back out again past the constriction point. So judging whether you have a true taper isn’t feasible that way.

A step-bore can be very effective, however, but the nature of these steps in a stalk of bamboo are organic/random and therefore difficult to use effectively. I’ve made step-bored wooden flutes where I can precisely control the location and degree of the steps, and even then taking advantage of it for tuning purposes is tricky. However, it can and does work when you hit the bullseye, but hitting that bullseye with stalk of bamboo seems like a long shot. The other tricky bit judging from your photo is that some of your finger holes are landing on the nodes where the walls are probably a lot thicker, creating a serious chimney depth. Larger holes and undercutting will help you, but I’m guessing you have to work a bit harder to get them balanced.

Also, the bamboo species that you are using is pretty far from being ideal, which you undoubtedly know already. Optimally, you would want a species that gives you greater inter-nodal distances and (if possible) thinner walls. Unless you live in a bamboo-rich environment this can be problematic. I have a bamboo xiao from a maker in Taiwan (the talented Winson Liao) and it is a fabulous flute. I was talking about this flute with one of his students (who loaned me the flute) who had visited Winson. I was remarking on how well this flute turned out and he commented that it all comes down to bamboo selection. Winson has a license to harvest all types of bamboo that are indigenous to his area, so he gets to cull vast amount of these canes, only choosing those that will lend themselves to making a good flute. For every one he selects he probably discards dozens. This is my own experience. Only a tiny fraction of bamboo stalks have flute potential if you are wanting a fully realized instrument that plays in tune through two octaves. It’s easy to make a “hippy” bamboo flute with a big, sweet voice that will play the first octave in tune–you can do that with all sorts of bamboo. But you are clearly going for something more sophisticated.

The final option is bore manipulation. I’m actually experimenting with a type of epoxy gel that would allow me to make minor tweaks to bamboo bores to optimize them since I don’t have the luxury of unlimited bamboo harvesting.

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What’s the effect of higher chimney depth on tone holes? I only know a bit about the effect of chimney depth on embouchure holes.

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Basically it means you need a bigger hole or some radical undercutting to get good intonation between the octaves. So if you are doing your finger hole placements and there is a big difference between wall thicknesses (comparing for example the A and the C# notes on a D flute, where the C# lands on a node) then the C# hole will need to be larger by comparison. And if you have insufficient bore taper, then the deeper chimney means that you will have to work harder to get the first and second octave notes in line with each other, likely have to undercut aggressively toward the foot of the flute. This isn’t necessarily a terrible thing, but it does mean more work for you and also the possibility of some unevenness of volume. I doubt that it would be enough to be a real problem, but it might be noticeable (bigger hole means bigger sound compared to a smaller hole adjacent to it). This is why the E hole on a D flute is always comparatively weak: the open end of a flute bore (or a series of larger tuning holes) are the equivalent to a really large hole, so that bell note sounds robust and huge compared to the tiny little E. Ideally one tries to keep finger holes away from nodes, but I admit that this is often impossible and I have had to plant finger holes right on top of a node in the past.

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Hi @Geoffrey_Ellis, thanks for the advice about the difficulty of finding the exact geometry for the bamboo.

I took a completely different approach altogether and had some success with my latest prototype.

I live in the tropics, so over the holidays I sourced some bamboo, a local species that had better internodal length with some slight taper that I used on the head part ala Boehm.

The taper improved intonation only subtly so I made a Tipple style wedge from bamboo using a sander, which allowed me to correct the top notes of the 2nd octave.

So the challenge now is to see if I can do it again.

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This is a great idea, and if one is faced with limited choice of bamboo (where you can’t cull relentlessly looking for the perfect taper) then making changes to the bore via some other method is the way to go.

The wedge method definitely works, though it is less optimal (in my opinion) than a genuine taper–at least that has been my experience. It can make the flute feel a bit stuffy, but this is on a spectrum and is attenuated by getting the wedge to have the right dimensions. Often times it only takes a tiny adjustment to bring things into better tune, so when I use a wedge (a rare event) I go as minimalist as possible.

As mentioned above, my experiments with epoxy gel aim to allow the introduction of a mild taper without using a wedge (or rather to enhance any existing taper that is already there). This is a bit tricky and I have not yet perfected it, but it has promise. It’s a similar principle to that used by shakuhachi makers who would make an urushi paste and gradually build up the bore of the madake bamboo to make a tapered bore. Only this is on a more modest scale and is less of a commitment (and stays away from the horribly allergenic urushi, which is close kin to poison ivy).