Andrew's blog

I learned how to make combs from friends with over 100 cumulative years of machinist experience! This is my low-tech, high-precision method of making exquisite harmonica combs. You can use this method to flatten the stock comb on your harmonica to make it play better.

The diatonic harmonica is made of solid pieces that must fit together in a way that is airtight. Mass-produced harmonicas often are not airtight and can be improved with a few minutes work.

This process is usually a little faster but the using a camera slows things down a bit.

Use this process on Hohner Bamboo Laminate (Crossover and Thunderbird) combs or the stock Suzuki Manji comb. You can also flatten a comb made of Corian or any other solid-surface material using this method. Be careful not to drop Corian combs - they shatter.

Wooden combs will swell. To flatten wooden combs like the Seydel 1847 or Marine Band Deluxe/1896 combs, I recommend you seal the surface after you flatten. Check for flatness after you seal, too.

Do not use this method on recessed-type harmonicas like the Special 20, Session or HarpMaster harmonicas. Those harmonicas use a different design concept. Checking and adjusting flatness on those combs requires a different strategy. Straightening and flattening the reed plates will make the best of the thin plastic combs in those models and will offer you great results. For perfectly flat reed plates, use The F Tool™.

This is the comb tool™. I meticulously flatten the top edge. *Only* the top edge is flat - we will be using that edge as a reference.

My comb tool is a working copy of a high-precision straight-edge (some call this a machinist square) precise to .000025" per 6" (25 millionths of an inch). The original stays in a drawer! If I were to use it on every comb I make, it would eventually wear out.

You can get a set of my comb tools here: Comb Tool™.

We will be measuring flatness along the left-to-right axis.

We will be measuring flatness along the up-and-down axis. That means in between every tine.

We will be sanding the comb surface. Tape a piece of 220 grit sandpaper to a flat surface. I use a granite surface plate but any flat surface will do. Don't obsess about the flatness of your working surface. The only thing you need to make your comb perfectly flat is a flat reference.

Place the comb tool over the comb to distribute the weight of your fingers evenly over the surface of the comb.

Move the comb around in circles in both directions until it feels smooth. This usually takes a few seconds. Flip it over and do the other side.

Place the reference along the surface of the comb and hold it up to the light. Hold it only on one side so that you can see how the other side behaves.

Switch sides. this gives us a good clue as to where the comb is bowed and where to flatten.

Put the comb down on the flat sandpaper and apply finger pressure where you want to flatten. Drag the comb along the sandpaper. Check flatness and repeat until it's flat.

Rotate the comb so that you are checking the tips. One tine is leaky here. Flatten the other tines to fix this.

Check in between each tine.

Switch your grip from side to side to reveal where the curve is.

Apply finger pressure and drag the comb to fix.

This is flat.

You can use the tool to apply even pressure to a portion of the comb - just like you used your finger. If the comb was unflat in this area, I would apply pressure like this:

Use this technique on both sides to fix a curve that is concave downward.

In summary, the hard part is measuring flatness. Once you can tell where the comb is not flat, it's easy to fix.

Extra tips!

Here are some extra tips on using my comb tool:

Comb tool extra tips page

This is part of a series about tuning the diatonic harmonica

Part 1 - Tune a harmonica using your ears and a simple chromatic tuner
Part 2 - More Better - ultra precision tuning
Part 3 - Perfect Pitch: Using breath dynamics for tuning
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The diatonic harmonica can be tuned to different temperaments.

Equal temperament is when each note is tuned to its exact pitch. When the notes of a chord are played together at ET, the chords can sound dissonant because the harmonics aren't in sync. Just intonation means some of the pitches are tuned a little sharp or a little flat so that when played together, the chords sound very smooth. The harmonics are in sync.

Here is a diagram of the waveforms of the tonic and third superimposed:

On the top, you can see that at ET, only one cycle is in sync. On the bottom at JI, every fourth cycle is in sync. That note needs to be 13 cents flat to sync up.

Here is a diagram of the the waveforms of the tonic and the fifth superimposed:

On the top line, at ET, only one cycle is perfectly in sync and we can see it rapidly go out of sync as you move away from the center. On the bottom line, every third cycle is in perfect sync. The interval of the fifth is a powerful sound (guitar players call it a power chord!) because the waveforms are in such harmony. But it only took 1.5 cents to disrupt the timing and make it sound less powerful.

There is no way you can tune a diatonic harmonica to within 1.5 cents accuracy by looking at the needle on a chromatic tuner.

Why?

Harmonica reeds don't always vibrate at the right pitch. If you apply too much air flow, the reed will vibrate too slowly and the pitch will go down. The note will sound flat. That's because you are making the reed move a lot further that it is designed to do (greater amplitude) and it has to travel a greater distance with every vibration.

Likewise, if you play the reed with much lower breath than intended, it will hardly move. Since it will only travel a short distance, it will make the trip is less time and the frequency will go up - the note will sound sharp.

Fortunately, there is a very large "sweet spot" where the reed responds to a range of air flow and can stay reasonably on pitch - within a few cents - even if you don't always use the same breath force to play that note. That's why we can play the diatonic harmonica with such a large range of dynamics.

The fact that the pitch varies by a few cents with breath force is both a curse and a blessing when it comes to tuning.

It's a curse because you can't just tune each hole to a specific note. You need to offset the tuning of each reed so that you meet the following criteria (to name a few):

- the single notes are on pitch
- octaves are on pitch
- the other intervals (fifths, thirds) are on pitch
- the three blow and two draw are enharmonic equivalent (the same note) but they are not the same note (blow three is a fifth, draw two is the tonic; each one has a different offset.)

To meet all these criteria you need high precision. That's where using dynamics actually comes in handy.

Longer reeds flatten more than shorter reeds as you increase air flow. When you play two reeds at the same time you can count on the lower reed to flatten more that the top reed as you increase air flow (because it's longer).

So if two reeds are very close to being in tune, say, they both register the same on the chromatic tuner but you hear beats when you play them together, you can tell which one is tuned higher by playing with increased breath force and listening to what happens.

- If the beating slows down or disappears when you increase air flow, the bottom note is a little sharp.
- If the beating gets worse with increased flow, the top note is a little sharp.

Here's another way of looking at it. This is an animated GIF of two waveforms superimposed. The waveforms are an octave apart. Both waveforms lengthen (drop in pitch) as breath force increases. The lower note in the octave is sharp but with increased breath force it goes into tune with the higher note for a short moment.

In this case, we should either tune the lower note a little sharper or flatten the higher note.

The effect of flow rate on pitch

Here's an example of using breath dynamics to tune with precision:

Warning: This blog post contains physics.

Here is an excellent demonstration of what happens when we bend notes. See what happens at the 3:00 minute mark.

When he finds the volume of the tube that is resonant to the frequency of the tuning fork, the sound increases. The frequency of the tuning fork stays constant though. Harmonica reeds are special because they can vibrate at different frequencies. We can make them vibrate faster or slower.

We apply “bending energy” by changing the size of the oral cavity just like professor Sumner Miller changed the size of the resonance chamber (cardboard tubes). Resonance is what applies kinetic energy to the reeds to make them vibrate at the desired frequency. If you want the reeds to vibrate slower, you open up your oral cavity to lower the resonance frequency. The reeds follow. It’s as simple as that.

Hopefully an understanding of what happens as you play a bent note can help you learn how to execute the technique.

Knowing the physics behind it allows you to free yourself from overthinking things. Don’t worry too much about tongue position, “U”-shape, “W”-shape, “G”-spot.... Just make an air pocket in your mouth and when you find the right size, the note will bend. Figure out what works for you to be able to re-create an air pocket of exactly the correct size every time you want to play that note.

It’s a little bit of a moving target when you consider that as you inhale, the tissues of your oral cavity will suck in and the air pocket will shrink. Conversely, the air pocket will grow when you blow bend because of the positive pressure. But with a little practice, your mouth will figure out how to keep the size of the air pocket constant despite these opposing forces.

Your ears play a big role in this. But the interaction between your voice, your ears and the shape of your oral cavity is automatic (or “autonomic”) so no instructions are required - other than to mention to make sure you can hear yourself play!

Overbends are just like regular bends!

Overbends are a little more complicated because we need both reeds (blow and draw) in the system to respond to the same resonance in different ways. One reed needs to stop moving while the other one needs to vibrate at the correct pitch. The trick is to get the reed that is standing still to stay still even though we are applying airflow to the system.

Sometimes out-of-the-box harps are set up to allow this to happen. Sometimes, they are set up to inhibit this. It’s the luck of the draw. It’s a common misconception than you need to practice overbends for years before you can become good enough to play them. The truth is that overbends require breath control, resonance control and a harp that is set up to cooperate.

It’s likely that you can learn to use overbends musically in a matter of weeks with the proper harp and some dedicated practice. You don’t need to build muscle over several years like a bodybuilder. You simply need to learn fine motor control.

I really enjoy watching professor Sumner Miller. Here is another video from the good professor where he describes the phenomenon of beating. Again, watch starting at the 3:00 minute mark:

Hearing the beating is a very important part of how to tune a harmonica.

The F Tool™ is now available in the Tools section

A well-playing harp has a solid connection to the vocal tract. A big part of what makes it is easy to play, sound nice and fat is that it's airtight.

If it leaks air, the connection between your vocal tract and the instrument is weakened and the harp feels stiff. The tone is also weaker.

The good news is air leaks are fixable! In fact, that's the fundamental step in improving a harmonica. If you skip this step, you will usually end up working against yourself further down the line.

The detailed instuctions on How to use the F Tool are here.

Can you tune a bunch of diatonic harmonicas with precision in the same room at the same time?

Of course you can!

https://harp.andrewzajac.ca/Tools

This is a moment captured during a harmonica repair workshop in Kingston, Ontario on 2015/05/16. The was the first time each of the participants used the French Tuner and I was impressed at how well they could tune a harp! Great job, guys!

I just bought a second CNC mill. It's bigger and faster than my first one. A second machine will improve my productivity and save time. It will also allow for redundancy. Routine maintenance won't affect my production time.

I bought it in the USA and crossed the border to pick it up the other day. I had to describe what I was bringing back to Canada to three different Border Services people and it's not an easy tool to describe.

Not being able to quite explain it in ten words or less, I said: "It's kind of like a 3-D printer".

Each one had the exact same reaction: "Really? Ahh! That's so cool!" they said and nodded...

I use my CNC mills to make combs, tools and a few other interesting tidbits I would never have conceived just a few years ago. Computer aided design (CAD) and computer aided manufacturing (CAM) is so accessible these days. Oscar Goldman was right! "We have the technology."