Several times I've had inquiries about how to repad a flute, or if I had any advice for those considering it. I've always warned people sternly away from trying it, and referred the more persistant to my favorite book on the subject, "The Complete Guide to the Flute and Piccolo" by Burkart & Phelan.
I've finally decided to post my thoughts as a kind of mini-howto--I do recommend that anyone interesting in trying this get the above book, and please don't try this for the first time on a fine professional-grade flute!!!
Repadding a flute takes a lot of patience, manual dexterity, and a few tools. It also takes listening to your gut feelings: if you feel that you're about to do something wrong, stop! and don't do it.
That said, here goes:
First, you're gonna need a feeler guage; I use a strip of thin cellophane wrapper (such as from a box of cough drops) glued to the end of a strip of cane that is about 1/3 of a clarinet reed. You can also use a match stick, toothpick...just about anything to glue the strip to. I like to be able to give it a good tug without it coming loose, so I usually glue it, then wrap the glued section with thread that is wet with glue just to give it some extra strength.
The easiest way and the way I recommend is to replace one pad at a time, then adjust the key, and have that key good before I move on. I start with the trill keys, then the C-natural key, and so forth on down the flute. The one exception is that unless the flute has a split-E, the “G” key mechanism has two pads that move as a unit and have no adjustment. These pads must be replaced and shimmed together, which can actually be one of the most challenging parts of a repad.
The smallest pads (the trill keys and C key) are the easiest. I like to “float them in” on melted shellac—you can also use various kinds of glue or wax for this. With the key off the flute, remove the old pad, and clean out the pad cup to remove any old adhesive or shellac. Wet the new pad lightly, and stick a pin or needle in the side of the pad—this serves both to hold the pad so your fingers don't get burned, and also will allow moisture to escape from the pad during play so it doesn't balloon up. Heat the key cup gently over a clean cool flame (bunsen burner is ok, I would avoid any but the coolest torches), and melt some shellac into the cup. Before it hardens, use the pin to place the pad into the pad cup and press it gently into place using a damp cloth so you don't get burned.
Then you put the key back on the flute—this is a good time to apply some key oil to the steel (the rod or axle the key turns on)--and carefully heat the key again until the shellac melts, and gently press the key down on the flute so that the pad “floats in” on the liquid shellac and gets a good seal. Once you're satisfied you have a good seal, wet the pad again and either clamp or use a cork block under the striker to hold the pad down firmly to its seat so that you get a good seat. Allow to dry for a few minutes and you should be good to go. The seating on these smaller pads rarely changes or requires any adjustment later.
As an interesting aside, it is also possible to use sheets of perfectly-faced cork instead of pads on these smallest keys. You float them in on the shellac the same way. They have the advantage that they last longer than pads and have a very definite firm feel under the fingers during play. The disadvantage is that they are more sensitive to moisture (cork swells when wet, of course), and they also add a kind of percussive “thunk” to the sound of the flute when they close. I personally prefer pads, but I've also done cork and it does work well. I have seen entire piccolos padded only with cork and they played beautifully.
You may be lucky if doing this with a fine grade flute: if the keys have never been bent—and don't get me started on the idiot repairmen that bend keys! it makes me want to choke them—then usually once you get one pad shimmed in the rest of the pads down the flute will be consistent and seat well with the exact same shims.
The process on the larger keys is to remove the mechanisms one at a time from the flute (being careful to note how it all goes together—if it's an unfamiliar flute, don't be afraid to make copious drawings), clean and oil the steels, and one at a time replace and seat the pads.
The larger pads don't float in on shellac, instead they sit on paper shims to place them at the right height to hit and seat easily. Try one full shim first, put the key back on the flute and press down gently. Make a small mark with a felt tip pin to mark which side of the pad faces the key arm, and replace the washer and screw, and also the resonator if there is one—it'll be a white plastic piece that fits over the screw. Check the key with the feeler guage at 12:00, 3:00, 6:00 and 9:00 o'clock. Ideally you'll feel the same amount of drag and pressure at all compass points. If it hits hard in the back, it's sitting too tall in the cup and you need to remove the shim. If it hits hard in front, it's sitting too low in the cup and you need to add a shim. If it his hard on one side or the other, you'll need to cut an arc of a shim, about 1/3 of the shim, and place it under the side opposite the side that hits too hard—if it hits hard on the left, shim on the right, etc. to raise that side of the pad.
You may need to sand on a shim to thin it down. You can also cut your own shims from newspaper.
If a pad hits hard in the back and there are no shims under it the pad itself is too thick—you'll need to purchase thinner pads if that happens. Some people try to shim them in anyway but I don't recommend it.
After you get the pad hitting pretty much evenly all the way around—and there is a little bit of leeway but not much—then you lightly wet the surface of the pad, and heat a pad slick or “pad iron”--just a smooth piece of clean metal will do, and move it quickly over the surface of the wet pad to steam out the wrinkles—just like ironing clothing to get the wrinkles out. Put the key back on the flute one last time—this is the time to oil the steel, too—and press down and hold for a few minutes to get your test seating. Note that you should also place one small pin hole in the side of each pad—I usually place it under the key arm—so that the pad won't balloon up from moisture.
As you go down the flute, you'll have to use the adjustment screws (if there are any) or the adjustment stops (more likely on a high-end flute). Use your feeler guage to check how hard pads that move together hit their seats. Ideally all pads that close at once should hit with the same force. If there are screws then you are lucky, as you just turn the screw to regulate the motion. If not, then you glue small pieces of paper under the adjustment stops to regulate the key motion, which is considered better but is considerably more time consuming (and frustrating!). As I mentioned before, usually the G mechanism has to be done as a unit—both pads at once—because there is no adjustment. This can be the hardest thing in the entire repad.
When you are done with a complete mechanism, wet the pads lightly and clamp or use cork blocks under the strikers to hold the pads firmly to their seats so they get their permanent seating. The regulation of the mechanisms will usually need to be checked and adjusted again after this seating.
That's it! After about 3 weeks of play, the pads may need to be reshimmed and reseated...this is normal. After that they should be stable and not move any more.
And be really careful with the needle springs—they really hurt really bad when they go under a fingernail or thumbnail! I can't count how many times I've done that.
Good luck—your first repad is usually scary as hell but you'll wind up with a flute that plays wonderfully. A well-padded flute requires only the lightest finger pressure to completely seal and will have a wonderfully strong, singing tone as a result.
--James
Edited to fix a typo: "pad click" was changed to "pad slick"
