Inside the NAF Flute

Ok so you have selected your flute blank wood stock.  We always start with two flute blank halfs.  Both halves are identical and hopefully a matched set from the same piece of wood.  Your first step is to layout the the flute so you know where the boring of the flute blanks will take place.  We do this by marking the flute blank with a pencil or pen and I will talk about each step.

When you are laying out your flute blank it is important to note that both the Blowhole and the Slow Air Chamber have NO effect on the tuning of your flute.  They do have an impact on the aesthetics of the flute and it will effect how long the total length of the flute is.  A proper length in your Blowhole and Slow Air Chamber are also important because the SAC acts as kind of an air bladder and a place for condensation from your breath to collect.  So here are our typical dimension for these two components.

Blow Hole – The diameter we use for most every flute we make that have a flute bore diameter of ¾”, ⅞”, and 1” bores is ⅜” in diameter.  We use a ⅜” roundover bit to create the blowhole channel in each half of the flute.  You will essentially bore half the depth in each blank and when you glue the blanks together you will end up with a ⅜” diameter hole.  The length of the blow hole again is up to you but we keep our blowholes between 2.5” and 3” inches long.

Slow Air Chamber – The diameter of this chamber will be whatever bore size you have selected.  So if you are making a ⅞” flute your SAC will also be ⅞” in diameter.  The length of the SAC can really be whatever you want it to be.  The longer the SAC the longer the overall length of your flute.  There are times though where I will cut the main bore for example at 1″ inch and the SAC I will cut at 7/8″ wide.  This usually has to do with how much taper I want towards the mouthpiece on a larger bore flute.  Typically though I will make the SAC area using the following length as a guide – based on bore size:

  1. ¾” Bore – the SAC is 3” – 3.5” inches in length
  2. ⅞” Bore – the SAC is 3 ½”  – 3.75” inches in length
  3. 1” Bore – the SAC is 4” inches in length

Main Flute Sound Chamber – The longest portion of the flute blank that you will bore is the main flute bore chamber.  This is where all the sound is going to happen so make sure you are careful when boring this section of the flute.  You are going to run the flute bore from the front of the solid block area all the way through the end of the flute blank.

Anatomy of the NAF Flute Side ViewNext Step After Boring Flute Components

After you have completed crafting the inside components listed above you will need to create the exit hole coming out of the SAC and the inlet on the front edge of the Solid Block.  These two areas are critical that you do a good job when crafting these parts of your flute.  Especially the front edge of the block which is where your cutting edge (true sound hole) we be.  One of the advantages of crafting your flute from two blank halves is that you have the opportunity to work on the inside of the flute to not only sand and seal the inside of your flute, but you are given the opportunity to fine tune the exit hole and entrance hole into the main flute chamber.

If you look at the schematic drawings above you can see that we have a light blue shaded area on one half of the flute blank only.  This is the half of the flute where you will construct the Focusing Channel and Cutting Edge on the top portion of your flute.  I have found that it is important to craft a sort of a ramp on the inside of the flute for both the exit hole leading from the SAC and a ramp on the inside of the cutting edge end.  I craft these two ramp areas with a very sharp gouge and I and very careful to blend the ramp into the two holes on both sides of the Solid Block.

I spend as much time as is needed to sand not only the bored areas of the flute but I pay special attention to these two ramps.  The goal is to create the smoothest path possible for your breath to follow, hopefully creating as little turbulence as possible when you play the flute.

We sand the inside of all parts of the blanks with at least 220 grit and then we seal the entire inside of the flute with Deft Sanding Sealer and then a Satin Finish follows.  I like the Deft products and we use their aerosol spray cans as they do a great job of sealing and they are easy to work with.  We put as many coats as needed in order to end up with a smooth finish throughout.  Be sure to mask off the gluing surfaces with Blue Tape prior to spraying any finish.

New to our production line of flute blanks is our new CNC Routed blanks.  One of the areas that we have focused on is the exit hole leading from the SAC.  In our CNC Routed blanks we have perfected a ramping method that almost eliminates the problem of a disturbed airflow leading from the SAC.  The better the path your breath takes leading from the SAC into the Focusing Channel the less turbulence will be created.

Crafting Windway & Cutting Edge (True Sound Hole)Crafting the Windway and Cutting Edge

This next topic is the most critical part of crafting a flute.  This is where all the sound happens and is created.  So taking your time in the part of your flute is an absolute must.  Making a mistake here can cause you some real headaches.  It is this part of the flute that most people have a hard time finding information on.  Many flute makers simply do not want to bother sharing this information with others.

Take a good look at the schematic above.  This schematic shows a side view of the Windway area.  What you are looking at is the Exit Hole coming out of the Slow Air Chamber and into the Focusing Channel.  Remember that there is going to be a fetish that sits on top of this area that will direct the airflow down the channel and onto the cutting edge.  So here is how I do this…

The first thing you need to do is to transfer some lines with a pencil across the top of the flute blank.  You are looking to mark the edges of the Solid Block area.  I like to then add about ⅛” in length to both ends of these marks.  This extends the marks that will guide you for placement of the exit hole and entrance hole.  So the exit hole coming from the SAC sits a bit back of the apex of the router bit curve and the same is true on the other end.

Focusing Channel Dimensions

The dimensions of the Focusing Channel should be approximately ⅜” wide and long enough to pass just beyond the front and back of the solid block.  The depth of the channel is very shallow!  About the thickness of a standard credit card works really good or about 1/32” deep.  This is important because if your channel is too deep you will allow too much air flow through the channel and you will end up with no back pressure which is not what you want.  If it is too shallow you will end up with too much back pressure and it will not play right either.  In addition if the channel is too deep then your cutting edge will have a hard time splitting the air flow properly.

Another thing to note has to do with the width.  I have discussed this topic with several flute makers that I respect.  Some say your focusing channel can be as wide as up to ½ the width of your flute bore.  For example if you have building a 1” inch bored flute your Focusing Channel could be as wide as ½”.  Some flute makers believe that a channel that is ½ the width of your flute bore makes for a better playing flute.  I for the most part start with ⅜” and try to keep it fairly close the that.  But you might want to experiment with your own building and see what you think.

The Exit Hole Dimensions

The exit hole is the hole you will cut that allows the air from your lungs to pass out of the SAC and into the Focusing Channel.  This exit hole can be just about any size you want as long as your fetish covers the hole and the channel properly.  We usually make the Exit Hole the same width as the Focusing Channel.  The standard length we make the hole is ⅝” in length measured from the mark that extends just past the apex of the router bore that we transferred earlier.

This is also where you want to create a softened ramp in the top of the flute that will help guide the air up and out of the SAC with as little interruption as possible.  We use a combination of a Dremel and small wood files to create the area and then we sand everything really well.  This ramp I am talking about is created at the apex of the very top part of the flute bore or a s close to it as you can make it.  Also – be sure not to encroach into the width of your Focusing Channel or you will end up having to do

Cutting Edge

This is the most critical part of the Windway process.  TAKE YOUR TIME with this part of the flute.  Start with the line you marked for the front edge of the solid block, from here you will measure forward (towards the foot of the flute) 6mm.  I use millimeters here because they are more accurate.  The hole you create here is going to be ⅜” wide or whatever width you Focusing Channel is and no more the 6mm in length.  If you have a drill press you can use a ¼” (6.2mm) square Mortising bit to create the initial hole.  Then you will turn the flute blank over and from the inside of the bore take a very sharp chisel that is no more than ⅜” wide and create a tapered edge from the inside to the tip of the front edge of the hole you just created.  You can also create the beginning of the cutting edge entrance hole using a smaller drill bit and fine tuning it using tools such as dremels, exacto knives, chisels or what ever you have in your shop that you prefer to work with.  But make sure the are VERY SHARP!

IMPORTANT POINT HERE – before you try to create the tapered edge find a place where you can clamp the flute blank down very tightly to a workbench.  You will clamp it with the inside of the flute facing up.  By doing this you will lesson the chance of splitting the top part of the flute where your edge is to be thus creating a real problem for you.  Be sure to use a block on top of the blank and clamp the blank using the block as a protective piece so you won’t mar your flute blanks gluing surfaces prior to gluing.

Start by taking your chisel and taking off very small amounts of wood at a time.  You want an angle that is approximately 40 – 45 degrees.  Your goal is to create a sharp wedge shaped channel that peaks at the front edge of the entrance hole.  Your distance from the front of the block to the very edge of your taper should not be too much more than the 6 mm you started with.  Ideally when you are done this distance from the front of the block to the cutting edge is approximately 7mm.  So what you end up with is an edge like the drawing above shows plus a very subtle ramp leading into and down the flute bore.

The final tuning will happen using a very small wood file and you will want to taper the top edge (from the outside top of flute blank) of the cutting edge and you will taper it gently downward until the very edge of this part sits in the approximate middle of the air flow coming down the Focusing Channel.  You should end up with a distance of about 7mm from the tip of your cutting edge to the front of the solid block area when finished.  If your opening becomes too deep then you will end up with a breathy sounding flute.  Which by the way – some people like so it is up to you how your flute is to sound and play.