Flute Shimming/Repad Question

MathGeek · Post by **MathGeek** » Thu Dec 04, 2008 11:09 am

Hello!

I purchased a well made, but well used flute. Prior to the purchase some of the worst pads were replaced.

I have used it hard, and some of the older pads now are in pretty rough shape. I am fairly logical, resourceful, and mechanically inclined, and I decided that since most of these pads requiring attention were on the footjoint, it was of lower risk and I would attempt to swap out some of the worst ones myself, as a learning experience. I have the new pads installed, shimmed, and everything works fine.

The question is -- in observing the installation of the pads on the rest of the flute, the amount of pad exposed from the key cup varies significantly from key to key. Can anyone give guidance about what is standard, or recommended, or even how to make a good decision about pad exposure? I would like my installation to be as close to correct as possible.

Thank you very much for your help.

pied_piper · Post by **pied_piper** » Thu Dec 04, 2008 12:16 pm

Pad exposure is generally based upon two variables: Pad thickness and shim thickness. However, using a pad that is too large in diameter can prevent it from fully contacting the bottom of the pad cup - that can cause excess exposure and excess surface wrinkles, too.

Pads are available in various thicknesses from about 2.5mm to 2.9 mm. When replacing pads, it's best to try to use pads that are similar to those that are removed from the flute (assuming that they are all even when you start). Using the right thickness of pad and shims also means fewer key height adjustments. Generally, the pad should be visible by a few tenths of a mm. If you carefully examine a pad you will see that the pad side edge is straight. Then it begins to curve a bit where it transitions from the side to the exposed surface. Usually, the curve should just start ever-so-slightly above the edge of the pad cup rim, but this can vary a bit from brand-to-brand.

Pads that are too thick or have shims too thick will cause the pad to have too much exposure. When this occurs, the pad will contact the tone hole at the back before the front which means it will leak at the front.

Pad that are too thin or with shims too thin will not have enough exposure. It will hit the front of the tone hole first and leak at the back.

When the pad is the correct thickness and the shims are right, the pad will contact the entire tone hole simultaneously. When satisfied the the pad is contacting properly, check each one with a feeler or leak light to be sure there are no irregularities where the pad can leak. Sometimes, the pad thickness is slightly irregular requiring the use of partial shims under various spots to make it perfectly level 360° around the pad.

MathGeek · Post by **MathGeek** » Thu Dec 04, 2008 12:40 pm

pied_piper wrote: Generally, the pad should be visible by a few tenths of a mm. If you carefully examine a pad you will see that the pad side edge is straight. Then it begins to curve a bit where it transitions from the side to the exposed surface. Usually, the curve should just start ever-so-slightly above the edge of the pad cup rim, but this can vary a bit from brand-to-brand.

So exposure begins relative to where the curve of the pad begins? I can do that. A couple of tenths of a mm works out to be about .001". So as I replace them, I will just make them all conform to those measurements.

Thank you for helping me out!

vampav8trix · Post by **vampav8trix** » Thu Dec 04, 2008 1:47 pm

That would work assuming that all of your tone holes are perfect and perfectly level.

It is a good place to start, but you will still have to go around and check for small leaks.

Good luck

pied_piper · Post by **pied_piper** » Thu Dec 04, 2008 3:45 pm

MathGeek wrote:So exposure begins relative to where the curve of the pad begins? I can do that. A couple of tenths of a mm works out to be about .001". So as I replace them, I will just make them all conform to those measurements.

Just to clarify, the amount of the exposure is not as critical as being sure that all of the pad contacts the tone hole simultaneously. Also, some repair techs will bend keys or pad cups to get the pad coverage rather than taking the time to shim properly. If that's the case with your flute, it may not be possible to get equal exposure on all pads with out re-leveling the pad cups.

MathGeek · Post by **MathGeek** » Fri Dec 05, 2008 8:01 am

pied_piper wrote:Just to clarify, the amount of the exposure is not as critical as being sure that all of the pad contacts the tone hole simultaneously.

Thanks for bringing out this fact.

There were significant differences in pad exposure - even across the footjoint. I suppose this is an artifact of onezy-twozy pad replacements. I was able to standardize the amount of pad visible and get a good seal with just a small amount of shimming.

I know I am fortunate. It appears that the toneholes are very close to level and none of the keys - at least on the footjoint - appear to be bent. I guess the flute has been serviced by patient techs. Hopefully the body will be just as well cared for!

After looking at the visibility differences on my (and other) flutes, I was really looking for a good starting point. I would hate to repad it and get it working beautifully only to, down the road, find out I did it all wrong.

Thank you for mentioning the importance of a good seal.

pied_piper · Post by **pied_piper** » Fri Dec 05, 2008 9:29 am

There have been several other posts that I have replied to on a variety of repair topics. You might find these posts of interest too.

viewtopic.php?t=2717

viewtopic.php?t=2401

viewtopic.php?t=2693

viewtopic.php?t=2683

fluteguy18 · Post by **fluteguy18** » Fri Dec 05, 2008 11:33 am

pied_piper wrote:There have been several other posts that I have replied to on a variety of repair topics. You might find these posts of interest too.

viewtopic.php?t=2717

viewtopic.php?t=2401

viewtopic.php?t=2693

viewtopic.php?t=2683

::sigh::

Never said it until now, but it's so nice to have someone who is so tech saavy on here regularly. There aren't too many people who are. I mean, I know a good bit, but to have someone around who really seems to know their stuff is nice.

sidekicker · Post by **sidekicker** » Fri Dec 05, 2008 12:58 pm

Yep -- I love that about this place. I wouldn't have known the answer to those questions either.

pied_piper · Post by **pied_piper** » Fri Dec 05, 2008 4:50 pm

Glad that I can be of help. There does seem to be a fair number of questions related to flute repair and maintenance.

I wonder if there's enough interest to justify asking for a new front-page category for repair and maintenance for the DIY folks?