General Remarks
This is the most important step when it comes to how the flute will sound. By working on the TSH, the sound can end up airy or clean, loud or quiet, contain more or less harmonics, etc. etc.
Basically … you are creating the flutes soul in this step. So take your time and experiment. I have build around 50 flutes by now and still have a lot to learn about all the parameters.
The Fundamental Note
After binding a bird on the sound area you should hear the first tone when blowing into the flute. Since there are no finger holes yet, this tone is called the fundamental note. I use an iPhone app as a tuner to find out what key this tone is.
Targeting a C4 minor flute, this tone should be a C4. Initially the tone will (hopefully) be lower because the bore is intentionally too long so far.
Using the flute that I am building for this tutorial I had a first tone that was a B3. This might be different when you are following this tutorial and depends on how long your bore is initially.
What you can also hear in the audio file is that the flute tends to overblow rather quickly when I blow slightly harder. This we will get rid off later …
The next step is to shorten the bore bit by bit to end up a little higher (10 cents) than the desired note. Why will become clear in the finger hole creation step. I cut off narrow rings of about 1mm with my band saw and check the pitch after each cut. You will get a feel after a few flutes how much you can cut off to get close to the desired note.
Make sure the ambient temperature is the same temperature the flute will be played later. This is important because higher/lower temperature will change the pitch up to a half note. I try to create 18-20 degrees celcius while I tune my flutes.
The final flute measurements when the fundamental was C3 + 10 cents:
1. Complete length: 750mm
2. Bore length: 550mm (measured from north side of TSH to foot/end)
3. Outer Diameter: 37.8mm
4. Inner/Bore Diameter: 29.5mm
5. Wall Thickness (average): 3.8mm
The final fundamental note C3 + approx. 10 cents after cutting off quite a bit …
Optimizing the sound
Now we optimize some parameters to optimize the sound. I usually want a very clear tone and the flute should only overblow if I want it to. You should play with the following parameters to find the right sound for the flute:
1. TSH Width
A wider TSH will create a louder sound but also has an influence on airyness and backpressure. Most people recommend 50% of the bore diameter. This would be 15mm in case of the 30mm diameter C4m flute I am building. I found a slightly smaller width of 12mm better for my taste.
2. TSH Length
A longer TSH will reduce overblowing tendency but will also introduce a breathy sound when it is loo long. I have found about 7mm to be good for the low flute that I am targeting (C4m). For mid flutes it seems like 5-6mm are a good choice.
3. Angle/profile of inner ramp from TSH to Bore
This is still magic to me and the influence is not clear but substantial. Anything between 30° and 45° should work. Another parameter to vary is how blunt the TSH-edge. A thickness of about 0.5mm is what I am usually ending up with.
4. Overblow
.If everything else seems fine and the width of the TSH is not too narrow, you can reduce overblow by creating a small ramp at the north side of the TSH (where the air enters the TSH). Be careful not to file off too much. Do it step by step and test the overblow behavior.
5. Smoothness
Everything should be as smooth as possible to allow the air to move without disturbance. At this stage of the process we can work on making sure all ramps and the flu are as smooth as possible by carefully smoothing all relevant ramps/parts with fine sandpaper. I usually wrap the sandpaper around a flat diamond file to give the sandpaper some guidance.
When the fundamental note sounds good and the flute behaves the way we want it to, we can start to create the finger holes.
In my case these were the final sizes:
1. TSH Width: 7.0mm
2. TSH Length: 14mm
3. Small ramp at TSH entry (1.5mm, approx. 45°)
The Finger Holes
I am using a software called WIDesigner (see software) to calculate the position and size of the finger holes. It is free and open source and I would like to use the chance to thank the creator Edward Kort for his great work. It can be downloaded here: link
The learning curve is very steep but worth it in my opinion. There are a lot of good video tutorials available on youtube that I would encourage you to watch (maybe more than once).
There are basically four important parts to prepare for the calculation:
1. The Fipple Factor
2. The Flute Measurements
3. The Tuning
4. The Optimizer
Part 1: The Fipple Factor
Having a flute with no holes but a working sound mechanism is the perfect start to figure out the fipple factor. This value is an abstract multiplier to adjust all later calculations for the specifics of your sound area. Please refer to the tutorial on how to determine it.
Step 2: The Flute Measurements (download file)
You need to measure the following things: TSH width/length, Flu depth, Wall depth, the diameter of the outer south end of the flute (termination flange) and bore length. We need to choose a reference point for all measurements and I always choose the north (mouth) end edge of the TSH.
Step 3: The Tuning (download file)
I am targeting a flute in the key of C4 minor. Therefore I created a tuning file with the following 6 notes incl. frequencies (C4, D#4, F4, G4, A#4, C5). You can download it here: link.
I guess it might help to specify all cross fingering notes but that is room for improvement later.
Step 4: The Optimizer (download file)
The layout of the finger holes should allow for comfortable playing and therefore I chose a maximum hole distance of 35mm, maximum hole size of 10mm and chose an optimizer that tries to keep the hole distances equal in two sets of 3 holes.
A smaller hole distance would be nice but does not seem to give good results with the key and size of the intended C4 flute.
Results
If you have followed all instructions and used the same tool sizes the following result for the finger hole positions might work for you. Your bore length should be around 553mm. Your sound area WILL be different than mine and therefore I would recommend to determine the specific fipple factor for your flute. But it might work if you just use the following measurements and compensate for the difference when you enlarge the pilot finger holes later. If you want to avoid understanding the software you can give it a try.
Drilling
The finger hole positions have to be measured starting from the north end edge of the TSH. I draw the center line of the flute and then create marks at the calculated hole positions using a measurement tape.
At these 6 positions I drill small pilot holes with a diameter of 5mm. In theory I could drill holes with the calculated target diameter but this will probably not work good enough. Therefore I just use the calculate hole center position and find the correct diameter in the next step.
Alternatively I am using my Desktop CNC machine to drill the pilot holes (see picture).
The final finger hole positions measured from start of TSH (north side):
Hole 6 – 173mm – 7.8mm Diameter
Hole 5 – 208mm – 8.5mm Diameter
Hole 4 – 243mm – 7.8mm Diameter
Hole 3 – 293mm – 9mm Diameter
Hole 2 – 328mm – 7mm Diameter
Hole 1 – 363mm – 6.5mm Diameter
I am pretty happy about the positions, spacings and hole sizes. Only hole 1 is a little small to my taste. I might shift it slightly down south about 1mm when building the next flute. But it still feels and sounds good.
Tuning
I am using the mentioned digital tuner software app and a dremel with a cone shaped sanding head (10mm diameter at the maximum width) for this step. The idea is to enlarge each piloted finger hole in turn until the desired pitch for each hole is reached.
Each hole is opened and tuned one by one starting with the first hole opened (hole 6, south). Unfortunately each newly tuned/enlarged hole will have an influence on the already tuned holes so we have to go back and fourth and check/retune all the already enlarged holes.
To increase the pitch you can either enlarge the hole and increase the diameter or just file an inside ramp on the north side of the hole (undercut). This has the benefit of not enlarging the visible hole if it is already big.
The notes in a C3m pentatonic scale:
C4 – all holes closed
D4# – hole 6 open
F4 – hole 6, 5 are open
G4 – hole 6, 5, 4 are open
G4# – hole 6, 5, 3 are open
A4# – hole 6, 5, 4, 2 are open
C5 – hole 6, 5, 4, 2, 1 are open
I will post a video of this procedure at some point.
To perfectly tune for cross fingering there is a more complicated way that is described here: link. Meanwhile I am using this advanced method to make sure all cross fingered notes are at least as close as possible to the desired pitch BUT I have tuned dozens of my first flutes with the simple method and after checking later, I found out that the cross fingered notes are not too bad without even caring. And you can play a million songs without cross fingered notes. Up to you …
The final finger hole positions measured from start of TSH (north side) including finger hole diameter after tuning:
Hole 6 – 173mm – 7.8mm Diameter
Hole 5 – 208mm – 8.5mm Diameter
Hole 4 – 243mm – 7.8mm Diameter
Hole 3 – 293mm – 9mm Diameter
Hole 2 – 328mm – 7mm Diameter
Hole 1 – 363mm – 6.5mm Diameter
I am pretty happy about the positions, spacings and hole sizes. Only hole 1 is a little small to my taste. I might shift it slightly down south about 1mm when building the next flute. But it still feels and sounds good.
