Q:  How do you get two Irish flute players to play in tune?
A:  Shoot one.

Tuning your M and E flute, or actually any traditional Irish flute for that matter, can be an extremely simple or an extremely frustrating experience, depending on your background and expectations.  We've found that folks like silver flute players, players that have played primarily in "concert" settings, and players with a very good ear can have a difficult time tuning our flutes.  On the other hand, people that have played a lot in session type settings tend to just pick 'er up and let 'er rip.
 

What note do I tune to?

The first point to note is that the D on M and E flutes is purposely tuned a bit flat. This is done to improve the sound in the lower register.  A good strong low D that can be blown loudly can be difficult to achieve, and is a good indicator of a high quality instrument.  Tuning the D a bit low helps this out (blowing hard on the low D brings it into tune).  So, when tuning your M and E flute, it is recommended that you not tune to D, but to a mid-range note, like A or G.

As experienced flute players can attest to, tuning your flute can still be a frustrating process, since regardless of what note you tune to, your tendency is to adjust your embouchure to pull the note into tune when tuning with other players.  The result is that you can end up continuously re-tuning as you chase the perfect pitch.

You can reduce your frustration in this area by changing your musical paradigm.  Maybe being perfectly in tune is not the most important part of playing traditional Irish music?  Hey!  Most of the tunes are played so fast no-one really can tell the difference anyway!  And on the slow pieces, you are probably going to pull the notes into tune with the other players as you go along.  A more relaxed attitude to this issue is to use your tuning slide to get pretty close for most notes, and then just compensate as you go.

Tuning Using the Head End Cork

There is a cork inside the head end of your flute.  If you pull off the cap on the end of the flute, you can easily see it.  If this cork gets dry, it can loosen up and slide around.  Then your flute will get really out of tune with itself (i.e., low notes not in tune with high notes).  To correct this, you can push the cork out and soak it in water and/or put some slide and joint grease on it so that it sticks firmly in the flute.  Alternately, you can wrap a few turns of plumber's Teflon tape (readily available in hardware stores) around the cork.

It can happen that because of the way you play your flute, the high and low notes will be out of tune with each other, even though the flute is in tune when it is built.  This can be corrected by moving the cork back and forth in the head joint just a bit until the notes are in tune.

Whether the flute goes out of tune due to sliding of the cork or because of your particular blowing style, the best way to correct the position of the cork is as follows:  First, play a low B with the left hand index finger down, then play a high B with the same fingering.  The two notes should be in tune.  Move the cork back and forth tiny amounts until the notes are in tune.  Note, also, that the high B should sound strong, and not fluttery or airy.

As a cross-check, you can also play the high B with the first finger of the left hand, and then play it by also putting down all three fingers of the right hand along with the left hand first finger.  These two B's should sound pretty close.

Usually, the cork is firmly lodged in the head piece and may require considerable pressure to get it to move.  In order to not destroy your flute in the process of tuning, the best thing to do is to go to a hardware store and get a dowel slightly smaller than the diameter of the tuning slide (5/8" works well).  You can now use the dowel to apply as much pressure as you need to the cork to get it to move.  When doing this, it is best to keep the barrel section slid over the tuning slide on the head end so that you do not damage the slide if things get away from you.

If you are a beginner on the flute, don't bother with this tuning stuff until you can get good strong notes over lower and upper octaves.  As your skill and ear improve, you may want to make further slight corrections in the cork to further improve tuning of your flute over its entire range of playing.