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 Air leak -
Author: steve1221 
Date:   2019-07-04 08:31

I seem to have a leak in the lower joint when I blow out - I can see one of the lower keys the 3rd one from the bottom that is supposed to be closed rise up and go back down. It has a felt / skin pad but it did this with a cork pad. The spring looks like a heave one and is fairly new. I tried bending the spring but still the same results - it seems that the air that I am forcing from the bottom with my mouth is too much. When I press on that key - I get basically an air tight seal. Anybody seen this ?

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 Re: Air leak -
Author: Chris P 
Date:   2019-07-04 23:39

If you mean the C# key, then that has to be sprung closed with a relatively heavy gauge spring going by oboe standards.

If it's an articulated C# (you can hold the RH C# key down and the low B/Bb closes it), then the pad cup is sprung open with a flat spring which is in turn overcome by the spring on the C# overlever which (like a fixed C#) has a strong needle spring. Make sure you use a suitable silencing material on the overlever as that has to be both durable and low friction - I normally use rubco/tech cork coated with graphite as that has both properties as well as keeping key noise relatively low. Natural cork will war through and Teflon will be too noisy on its own, but thin self-adhesive Teflon sheet can be laminated on top of rubco.

Chris.

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 Re: Air leak -
Author: steve1221 
Date:   2019-07-05 09:22

thanks Chris

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 Re: Air leak -
Author: steve1221 
Date:   2019-07-05 09:23

but I dont have a flat spring holding the key down just a heavy needle spring

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 Re: Air leak -
Author: Chris P 
Date:   2019-07-05 18:36

That's a fixed C# key if it's only got a needle spring keeping it closed and with the pad cup soldered directly to the key barrel.

If you are blowing air into the joint under high pressure with the open-standing keys held closed, it's inevitable one of the closed sprung keys (the F key and fixed C# in this case) will blow open with the air pressure. The Eb and forked F vent shouldn't blow open as they're held closed by other keys.

How well does the lower joint hold a vacuum when you do a vacuum test?

Chris.

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 Re: Air leak -
Author: steve1221 
Date:   2019-07-06 05:13

the vacuum test is not good at all - but all of the pads are closed and I dont see any light from the pad/tonehole area when I press down normally. I just put new pads but I made them from a new wine cork that I have - it is good because there are no pits in the cork - but just the same I have a new pad set coming in. - I dont know where the leak could be from there are no cracks in the wood although the seller said there was a repaired crack - I cant see it - he said that it did not go through the wood body. Do you think skin /felt pads would be better for the lower joint ?

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 Re: Air leak -
Author: Chris P 
Date:   2019-07-11 22:14

Wine corks aren't the best things to make cork pads from as they're not high quality cork and have pores running parallel with the surface that can cause dips or leaks if the surface layer is thin and there's not much support under them.

You're best using commercially available cork pads made from high quality cork with as few imperfections as is possible (hence the massive increase in price with the increase in diameter).

Even with the best quality pads, you will still have to prep them to make sure they're both flat and have no imperfections on the face of them and likewise the tonehole bedplaces are level and defect-free to ensure a perfect airtight seal.

Some people believe cork pads are prone to leaking, but that's a lie and usually spouted by people who have little experience of using cork pads and installing them so they seal well. I prefer to cork pad oboes throughout and prefer never to use skin pads, only using leather pads for the three largest pad cups if I have to.

Another thing that will compromise things is if key fitting is sloppy, so make sure key fit I done to minimise any rocking by swaging key barrels on their appropriate rod screws. Some keys do require lateral play between the pillars - usually the cross mounted keys (1st 8ve rocker, side G#-A trill key, forked F vent and its rocker, low Eb and C# pad cups) as they're the first ones to bind up with changes in humidity. On plastic oboes you will need lateral play between keys and pillars on all keys relative to their lengths, so keys with longer key barrels need more lateral play compared to short key barrels to be sure nothing binds up when playing outdoors or in cold churches.

What tools have you used to get your toneholes level and how to you prep your cork pads to make sure they too are all nice and flat?

Chris.

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 Re: Air leak -
Author: steve1221 
Date:   2019-07-13 07:15

Thanks Chris - I have made some nice pads with new unused wine cork - but ones without pits are hard to find but I have a few. I made a holder out of a furniture screw because it has a long shank not threaded and a big flat head. I contact cement both the cork and the screw and put in my bench motor and sand away. I use 400 grit to get the diameter close then finish it with 2500 sandpaper, and the face is just sanded flat with a stiff sand board - while I have the pad on the holder I use a feeler gauge with 400 grit paper glued to it to make a bevel. Then cut it off with a razor blade. Then I check the thickness to what I want and sand the front smooth. And for thinning out the pad I sand the back only till I get the desired thickness.
I did find the leak in the lower C# key using a light - and I am waiting on a pad set that will come in. From China but I found 2 places in the USA that I can order cork sheet and blank corks, so Ill do that from now on. Because this wine cork thing is too much work. You are right the ones you buy are better.
As you can tell I make my tools and only purchased a pair of smooth duckbill pliers. But I am not a professional.



Post Edited (2019-07-13 08:10)

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