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 Post subject: Cheap and dirty keypads
PostPosted: Sat Jun 08, 2019 5:22 pm 
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Ok this is bad I admit. But it works.

A while ago I bought an old eight key wooden flute of unknown origin on ebay. I've been gradually getting to know it and learning about the instrument by fixing it up. I don't think it's designed to play at A 440, because when I get the G in tune everything else goes south in a hurry. But if I set the stopper where it's supposed to be and set the tuning slide more or less in the middle it plays a Ab of wavering uncertainty. I took the old cork out--it was all bollixed up with glue, but when I took it off and cleaned it it had a working screw mechanism for adjusting the cork. I made a new stopper and have been experimenting with placement. Need to be more systematic

The keys mostly leaked so I've had most of the holes filled with tack-it. I was looking around for something that might work as a pad and voila--foam earplugs. They cut easily and they're tapered, so you can easily get them to the size of the key cup. Hot glue holds them in place. At least this way I can get used to what the keys actually do. I have a ton of them in my workshop--theyre' cheap and the purple ones don't look too garish.

I'm still not sure how much work this flute is worth. It has a nice patina of age and it's a pleasure to play--sweet and not too loud--when it's in tune that is. But it's got all kinds of problems, like the brass tube lining the head moves out of position easily. That can't be good!

It's fun though and I'm going slow and learning


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PostPosted: Sat Jun 08, 2019 5:44 pm 
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Now I would imagine that earphone foam would be open-cell foam, in which case I'd expect leakage through it to the great outdoors. Easily checked by using a suck test. Cover the far end and the finger holes and suck on the open end. You shouldn't be able to perceive any leakage. If you can, take the keys off, cover the keyholes with blutack (or your true-love's fingers) and repeat the test. If there's still leakage, track it down and kill it! If not, I'd suspect the foam.

Some makers some time back were advocating kayak foam (whatever that is), but I'd still be dubious until convinced. Not only must we avoid any leakage, we don't want to expose the side of our vibrating air column to a sound absorber. Normally our small pads won't absorb much sound energy, but it's worth keeping in mind as a potential minor source of loss. If you look at the large pads on a sax, you'll see they have hard discs rivetted to their face. These are called resonators, because they boost the resonance of the air column when compared to plain pads. These "resonators" don't resonate themselves, they just reduce the absorbitivity of the naked pad.

If your foam pads do leak, you could try giving them a smooth leakproof face. Say cut a disc of plastic electrical or duct tape and apply it to the face of the "pad". Don't know how long it will last....


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PostPosted: Sat Jun 08, 2019 5:53 pm 
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Terry McGee wrote:
Now I would imagine that earphone foam would be open-cell foam, in which case I'd expect leakage through it to the great outdoors. Easily checked by using a suck test. Cover the far end and the finger holes and suck on the open end. You shouldn't be able to perceive any leakage. If you can, take the keys off, cover the keyholes with blutack (or your true-love's fingers) and repeat the test. If there's still leakage, track it down and kill it! If not, I'd suspect the foam.

Some makers some time back were advocating kayak foam (whatever that is), but I'd still be dubious until convinced. Not only must we avoid any leakage, we don't want to expose the side of our vibrating air column to a sound absorber. Normally our small pads won't absorb much sound energy, but it's worth keeping in mind as a potential minor source of loss. If you look at the large pads on a sax, you'll see they have hard discs rivetted to their face. These are called resonators, because they boost the resonance of the air column when compared to plain pads. These "resonators" don't resonate themselves, they just reduce the absorbitivity of the naked pad.

If your foam pads do leak, you could try giving them a smooth leakproof face. Say cut a disc of plastic electrical or duct tape and apply it to the face of the "pad". Don't know how long it will last....


Thank you!

The foam compresses a LOT, so maybe that's why I seem to be getting a good seal. I've tried the blow test, not the suck test-- and it seems good--i'll keep testing. It's very enlightening.

Also playing this flute--when it works--makes me think one of your Gray Larsen models might be just the ticket. I'm not a young guy and I'm starting late and easy to fill is an attractive option


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PostPosted: Sat Jun 08, 2019 8:15 pm 
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Yeah, being such light foam, even though it's open cell, it may well end up collapsed cells, and seal well! But do the suck test to be sure (to be sure....).

To be good at repairs, and even more so for restorations, you have to get really suspicious and forensic. People usually have a reason for sending a flute for repair - "the bottom note is weak", or something similar. They might even have worked out why, e.g. "the long-F key is unreliable in closing". And they might be right. But they haven't spotted the 5 other things that are wrong with their flute, because they have got used to them over the long period over which they manifested. So, fixing the presenting fault is usually only the starting point. Keep going until you can detect no leakage in any piece, and then in any pair of pieces. (An elusive fault is a split in a socket that only leaks when the tenon is inserted.)

Flutes suffer from the "Death of 1000 cuts" - a tiny crack there, leaking pads here-and-there, weak spring here that allows the flute to pass the suck test (but not the blow test or the Magnehelic Leak Detector), roughened bore that introduces aerodynamic drag, distorted bore (particularly under wrapped tenons) that can introduce tuning issues, instability and poor resonance, tuning slide slightly protruding into the embouchure hole producing noise and reducing efficiency, sloppy keys that sometimes close fine but othertimes leak like a sieve, etc, etc, etc.

We should probably all check our flutes more often! Every year, when you go for your medical checkup, check the tyres on the car and check your flute...


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PostPosted: Sun Jun 09, 2019 2:04 am 
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Quote:
Now I would imagine that earphone foam would be open-cell foam, in which case I'd expect leakage through it to the great outdoors.


Closed cell foam is used on keys on the Uilleann pipes by some makers and is highly effective in that context.

Slices of old camping mattresses etc.

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PostPosted: Sun Jun 09, 2019 3:59 am 
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Yeah, I reckon pipes would have a lot more latitude than flutes in this regard. The tone generator (the highly-pressured double-beating reed) is a lot more robust than our wafty "air-reed". The keyholes are probably smaller too, exposing less of the absorber to the vibrating air column. And the wall thickness greater, distancing the absorber. The air column is much shorter too (1/4 wave, rather than 1/2 wave) making it more robust. The benefits of being pressure-driven, rather than flow-driven. Note that the flute family (including whistles and recorders) are the only instruments that work on flow. The other woodwinds (clarinet, oboe, bassoon, etc) are all pressure-driven.

Heh heh, when you think of it, we are dead lucky flutes even work! Now wonder we have to mollycoddle them so. Thank your flute today!


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PostPosted: Mon Jun 10, 2019 9:27 am 
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I use the so-called "kayak" foam. Its a closed cell fine grained neoprene that accepts the impression of the hole very well, changes should the position of the key relative to the hole change, and is quite durable. I but it in 2" thick blocks from a local kayak rental outfit where it is sold as flotation. I fill the keycups with baking soda and superglue, sand them flat, and then superglue disks that I cut out of this material onto the flat surface, and sand them to the final thickness.

There is no diminishment of the sound from the foam surface. That could be an issue in modern flute sized pads possibly but on these wooden flutes with tapered bores the holes are quite small. The fact that they seal so well helps the tone, more than any theoretical diminishment of tone quality.

Rod Cameron uses this method on his flutes, which is where I learned it.

Casey

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PostPosted: Tue Jun 11, 2019 4:13 am 
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Casey Burns wrote:
I fill the keycups with baking soda and superglue, sand them flat, and then superglue disks that I cut out of this material onto the flat surface, and sand them to the final thickness.


That certainly sounds like an approach that will minimise any side effects, Casey. The foam depth is very limited, and the thin foam backed up with solid stuff, not a cavity or deep foam.

It would be interesting to take a large-holed keyed flute, eg a Prattens, with either trad leather or thin kayak foam pads as you've described and measure the efficiency of the resonance. Then add "resonators", like the sax pads have, and measure and play again to see if we could detect the difference.

Instinctively, I feel keyless flutes have a slight edge on keyed flutes, presumably due to some losses due to the key holes. (This is perhaps controversial, as I remember some writers way back arguing the opposite should apply, but I was never taken by the arguments.) Whether these losses are due to pad absorption, key hole turbulence, spring trembling or something else would take some careful study to determine. And of course could come back as "all of the above".


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PostPosted: Tue Jun 11, 2019 5:34 am 
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I found replacing a pad (I got it sticky with oil) on my Burns flute incredibly easy. Some heavy-duty double-sided tape (for carpets) was nearer to hand than adhesive so I used that and four years later it is still fine.

I would had more trepidation if Casey had not told me that I would find the cup filled flush.


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PostPosted: Thu Jun 13, 2019 12:22 pm 
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Is there any reason why people don't cast little silicone keypads? It's a great, non-porous material available in all sorts of firmnesses and colors, seals well, and will never wear out!

It also occurs to me that with some clever keycup design, they could be self-retaining and need no adhesive.


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PostPosted: Thu Jun 13, 2019 12:39 pm 
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MadmanWithaWhistle wrote:
Is there any reason why people don't cast little silicone keypads? It's a great, non-porous material available in all sorts of firmnesses and colors, seals well, and will never wear out!

The sealant types of silicone I'm familiar with, might have a problem with too much "stiction" where it doesn't release quickly enough. It's a tricky requirement for key pads; you want a tight seal when closed, but an immediate release for smooth key action. Of course there are probably many different ways to adjust silicone formulas, so maybe there is some ideal type that would work.


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PostPosted: Thu Jun 13, 2019 4:09 pm 
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We have an inexpensive plastic boehm flute with silicone key pads. They seem great, and I don’t notice any stickiness, but I’m not much of a judge of the boehm flute


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PostPosted: Thu Jun 13, 2019 10:34 pm 
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I purchased an antique flute restored by Patrick Olwell in the mid nineties. He set silicone key pads in that one as an experiment. It played well for me for a year or so, then I passed it on to a friend who played it for more than a decade. I don't see it done much anymore so the material may have been abandoned for some reason. There might be one formula of silicone better than another.

There may be a thread on the process here if you do a search.


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PostPosted: Sat Jun 15, 2019 5:28 pm 
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I remember in my very early days using silicone rubber to pad a flute. The tricky thing was getting a smooth enough face. But then I tried leather pads and never went back.

You can buy commercial plastic foam pads, made by Pisoni from memory. I have tried them, but didn't find them very successful. They're made up from a cylinder of fairly dense foam with a self-adhesive backing and a thin plastic "skin" for the mating surface. They probably really need well-aligned cups with a flat back to work well.

We shouldn't forget the other side of all of this - the key seat. In a lot of the repairs I do, I find the key seats have been really poorly cut. (I'm talking mostly 19th century flutes here, but I have been taken aback by some modern flute key seats too!) I often end up having to recut seats as nothing would permit a pad to seal against missing chunks of wood. What inevitably amazes me is how well seats in cocuswood cut with an adequately sharp cutter - they glow like shining jewels under the work lamp compared to the dull wood around them. And then seat and seal easily and soundly. So, anyone planning to do a lot of restoration, it would be good to make up or buy a set of seat cutters, or find a well-equipped woodwind repairer who could undertake that task for you. It can be the difference between an "almost workable" flute and a very good flute.


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