Wednesday, October 10, 2012

Checking for Leaks

Feeler gauge with Mylar
If you walk through the finishing department at Powell, you will undoubtedly find our finishers "sweeping" a little stick around each pad several times -- or at least this is what it may look like from afar.  But, this small, very manual device is actually a feeler gauge -- and the finishers are checking for leaks.  You have probably heard a few repair technicians, fellow players, and teachers talk about leaking pads, and our finishers make sure that there are no leaking pads on the flutes that they are finishing.

So, what exactly is a leaking pad?  Well, it can seem a bit misleading, since it's not exactly the same as a tire leaking air.  When checking for leaks, it's actually the pad seal that is being tested to make sure there are no leaks.  In simpler terms, when the key cup closes and the pad covers the tone hole, are there any gaps between the pad and the edge of the hole?  The answer should be no, because we all know what the result would be... You see, the air you put through the flute could escape or "leak" through if the pads are not sealing against the tone hole, and you would find it difficult to play the notes you are expecting to come out! 

Using the gauge around the pad to check for leaks
Finishers and repair technicians have different techniques for checking for leaks, but we caught up with finisher Karl Kornfeld at Powell.  He showed us two feeler gauges which were both small "sticks" with a feeler paper on the end.  One gauge used cigarette paper, which is .001 of an inch thick.  This is the traditional type of gauge that you may have seen your technician use or that you may use yourself.  The other gauge, which is the one Karl and the other finishers use, has a piece of Mylar at the end.  Mylar is .0005 of an inch thick, which is definitely thinner than the cigarette paper and (therefore) more precise in detecting leaks.  Karl uses a general "sweep" around the pad with the gauge to see where there may be leaks.  He then goes around the pad clockwise, drawing the gauge out to check various spots.  He says the pressure should be even as you check, and you should draw the gauge out with the same motion -- just to keep everything consistent.  Although he usually begins checking pads with a "sweep," in the video below, you will see him draw the gauge, then circle around with the "sweeping motion," and repeat the drawing motion.  Oddly enough, he also told us that Mylar is the same material used in Pop Tart wrappers!  Obviously, the Mylar on the feeler gauge is much, much thinner --- thank goodness.

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