A short off-CF chat with one of our members here is making me ask this: how does the sharpness or otherwise of the embrochure cut (the blowing edge) affect playability? Can you imagine a too sharp cut which would make your flute less forgiving?
Levente
Hi,
For my embouchure cuts, the blowing edge is very sharp, I will round it with 2000 grit sand paper. I have played antiques that the edge is worn, they still play fine.
More important is the angle of the blowing edge wall, if that is to steep an angle it will sacrifice the bottom D, not steep enough, and the second octave is weak.
Just my 2 cents worth… 
A very sharp edge normally increases the amount of “noise” (hissing) that is audible while playing. But if the entire acoustic system of embouchure, bore and tone holes is set up well, i.e. hasn’t too many flaws that cause turbulence, there is no reason why a razor-sharp edge should be a disadvantage, it actually often makes the higher registers considerabily easier to reach. On the flutes and headjoints I make, I leave the edges rather sharp as many people prefer it that way. On my own flute the edge is a bit rounded off, as this makes the embouchure more resistant to high-power blowers like me. All in all, the blowing edge has a rather minor influence on how an embouchure hole works.
Jon,
when you say too steep, do you mean closer to 90’ (straight off the drill press) or closer to 45’. I just can’t decide which way is ‘too steep.’
Sorry, I meant if it is more undercut it weakens the low register, and if it is less undercut it weakens the upper register. You usually start with 5 deg all the way around then increase the angle on the blowing edge wall.
Best summary of the whole embouchure hole matter I’ve seen so far. Very useful for tomorrow’s class, as I think I get to cut the embouchure hole any moment now.
Thanks, Jon, thanks Gabriel,
And how about the sweet spot? Anyone here feels a sharper cut makes it more difficult to find the sweet spot and maintain the right angle/direction of the airstream while playing?
Levente
The term “sharp embouchure cut” can refer to either a sharp edge or a sharp angle, both of which have been referred to above. I prefer to round off the blowing edge a wee bit with very fine sand paper or a #4 Swiss needle file. As has been said before, this helps to reduce some of the hiss and it also makes sense in terms of durability, as very sharp edges in softer material, such as wood, are hard to maintain. That is why this edge is sometimes fashioned from harder material inlayed into the softer material of the headjoint.
I don’t know if there is such a thing as a standard embouchure blowing angle. Yamaha in their flute catalog pages offers a number of different embouchure shapes and cuts with various embouchure blowing angles, all offering a different blowing response and tone. Terry McGee also discusses this in his online flute pages. I think that Jon’s comment about slightly more than 5% from the vertical is probably close to “normal” for Irish flutes, if there is such a thing as normal. I have seen 7% mentioned in this regard. However, I often cut the embouchure angle quite a bit more than this, and I like the resulting increased volume of the flute, although it may take more air and be somewhat harder to manage, all things considered. I think that a lot has to do with what you become accustomed to. I am currently experimented with reducing this angle back a little closer to 7%.
I think the conical flute benefits more with less of an angle on the blowing edge wall, as the flute is blown more into the embouchure instead of across the embouchure hole. The sweet spot can be increased by undercutting the embouchure on the upper and lower edge of the blowing edge wall. The hole remains oval, but the under cut is widened to increase the sweet spot. Like Doug said you can make a slight dome on the blowing edge wall, it is very slight. Mainly you just have to make slight adjustments to get it right. the trick is to not do too much! 
What’s the effect of making the wall thickness of the head joint thicker or thinner (which would affect the thickness of the embouchure hole)?
This is very interesting to me. Could you elaborate?
Wild speculation.
Perhaps turbulence results? Looking at planes subsonic planes have rounded edges. The sharper edges on supersonic planes cause turbulence at sub sonic speeds. Granted, turbulence is what we are trying to produce, but perhaps sharper edges favor higher frequencies and harmonics?
End of speculation.
I don’t think that the question is being ignored, just in process. Embouchure chimney depth is another variable in the complex flute embouchure equation, although it doesn’t really fall in the topic of “How sharp is too sharp?” I’m still thinking about this. I discuss this with reference to my flutes on my Optional Lip Plate Headjoint page. Anybody else still thinking?
Thread edited, back on track. Carry on. - Mod.
Thanks for that link Doug. I think the question is pretty much within the real “fall” of the topic because the deeper the chimney the greater the scope to gradate the edge or bluntness and everything in between.
I thought deeper chimneys worked better for lower notes, and shallow ones made the upper octaves easier to hit. It might so similar things to the harmonics that are stressed.
Still waiting on this one, guys.
You may think differently if you heard a well made D key baansuri (typically thin walled bamboo with shallow chimney) - work excellently for low notes. Don’t just believe me or not. Ask any player who plays Irish flute well and also plays baansuri, take
http://www.colingoldie.de/jean-michel-veillon.html for instance.
Bansuris have a huge bore, I wouldn’t compare them to Irish or modern flutes…
I think if you stop thinking of baansuris as the B key flute only and compared a D key baansuri with a cyclindrical bore Irish flute as in Doug Tipple’s flute you will notice your bore comment may lose its punch.
Secondly, and most importantly, if you truly consider that good low notes can be explained by factors other than chimney depth, then, ironically, your challenge to my post itself supports my speculative response to I.D.10-t’s thoughts.
Finally, if, based on your limited experience with them, you still feel my baansuri comments irrelevant to an open topic about embouchure cuts on flutes, then I could just rework my earlier post to say,
You may think differently if you heard an Olwell (typically bamboo with shallower chimney than wooden flutes) - work excellently for low notes. Don’t just believe me or not. Ask any player who plays wooden Irish flute well and also plays a bamboo Olwell.
to make exactly the same sort of point.
http://www.firescribble.net/flute/olwell.html