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 (click to enlarge). 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.
NOTE: I have discussed this topic with several flute makers that I respect. Some say you’re focusing channel/Cutting Edge 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 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.
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 as 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 make some adjustments.
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 initially. 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, Xacto 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 work bench. You will clamp it with the inside of the flute facing up. By doing this you will lessen 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 – 48 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 6mm you started with. 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.