Bent pad cup

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HMannfan
Posts: 73
Joined: Fri Nov 01, 2013 10:55 am

Bent pad cup

Post by HMannfan »

One of the pad cups on my Armstrong flute is bent. I can get the pad to seat tightly at 12 o'clock and 6 o'clock, but it is leaking at 3 and 9 o'clock. I used a glass microscope slide to test for flatness and found the pad rocking side to side while hitting at 12 and 6 o'clock. I want to avoid using partial shims whenever possible.

How can I go about leveling this pad cup? Ferree's sells a set of flute pad cup tools (part #N78), but I'm unsure whether this is what I need nor am I sure how to use them. Any help would be appreciated.

mirwa
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Re: Bent pad cup

Post by mirwa »

If the contact is good at 12 and 6, and 12 being the hinge arm connection point, then you have a few options.

Identify if the damage is the tone hole / key cup / pad

When you've identified the cause you can start the repair.

If the damage is the tone hole, you can either raise the tone hole rolled edge or lower the corresponding key contact points with shims

If the damage is the keycup then you can straighten the key cup or raise the applicable low areas with shims

If the damage is the pad, you can rotate the pad and check again, or replace the pad

Steve

HMannfan
Posts: 73
Joined: Fri Nov 01, 2013 10:55 am

Re: Bent pad cup

Post by HMannfan »

Thank you Steve.

I've narrowed the problem to the pad cup. The question at this point is what tools and techniques to use to take the slight bow out of the pad cup. I am at a loss as to how to proceed. Can you offer any suggestions?

fluteguy18
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Joined: Sun Jul 16, 2006 3:11 pm

Re: Bent pad cup

Post by fluteguy18 »

You don't. You shim the gaps. Otherwise you're just causing damage unless it's obvious the pad cup has been damaged. Pads and toneholes are never truly flat. The interiors of pad cups are seldom flat, and the rims of the cups are seldom uniform either (once you start truly measuring). That's why we shim the difference with a combination of whole shims (to set your pad protrusion to minimize the amount of shimming needed) and partial shims (to close the gaps).

mirwa
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Re: Bent pad cup

Post by mirwa »

I do not like to contradict our newest learned friend, as he is undertaking a repair course, however I do dis-agree, you must remember there are many ways to skin a cat, and the course teaches you the most agreed upon way amongst peers in the field and design time of the course.

Levelling a keycup is not hard with practice, small mandrels and doming punches will suffice nicely. The point to remember as your working the surface of the keycup is not to worry about the rim of the cup, but the back profile in relation to the key hinge, with experience you start to make your own tools that allow the shaping of the keycup whilst the key is fitted to the instrument, but again you must know where the damage is and not assume you know without any physical confirmation.

Shimming is fine by me as well, it has a purpose, but IMO, I do not like using any partial shim greater than 0.002 thou, as I feel if greater than this size, it introduces two leaks albeit smaller on the ends of the partial.

The best way to test ones skills is with a magnehelic, learn to set a pad for closure with a light touch and a reading of 1 on the magnehelic, then maintain this on a repad throughout the whole instrument, if you can do this then the instrument will absolutly sing

HMannfan
Posts: 73
Joined: Fri Nov 01, 2013 10:55 am

Re: Bent pad cup

Post by HMannfan »

Thank you both, fluteguy 18 and Steve.

Fluteguy 18--I have enjoyed your postings, videos, and pictures on your "aclassicaljourney" site. I look forward to your working on a flute in the future (I hope). It was your posting about swedging hollow key tubes on a clarinet that helped me understand that process. Thanks again.

Steve--I am trying to avoid using partial shims, but in this case it will be impossible. After reading your last reply it has become obvious to me that attempting to adjust any minor defect in a key cup is not worth my trouble at this point, and is well beyond my skill level. I'll just partial shim it until the pad seals properly. Thanks too, for your comments concerning magnehelic readings. I have been conscientiously using a reading of below 1 on the magnehelic as an indicator of good pad sealing. Thanks a lot Steve.

fluteguy18
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Re: Bent pad cup

Post by fluteguy18 »

Mirwa: by all means! Disagree! It takes all kinds doesn't it? I'm still learning and I'm sure your techniques work if your mag readings say they do. I personally resist adjusting metal if at all possible. We both know that metal can only be flexed so many times before the molecular structure becomes so fractured that the part eventually cracks and breaks. That's why I prefer shimming if the pad cup hasn't been damaged to my knowledge. On that note however up to this point I've seldom needed to use partial shims greater than .003" and they weren't very large.

Point of interest: I've been going through and tweaking the clarinet that I overhauled last semester. It read a 1 on the Magnehelic gauge. My instructor challenged me to get it down to a zero. So naturally... I accepted the challenge. Today I had the lower body joint to where it was 1 notch above zero (a 0.25 out of 10). It took me a while, but I found the leak. There was a pinhole in the pad skin that was letting air leak through the skin, through the felt, and out the pinhole vent on the rim of the pad. Maddening! :lol:

Oh! And here's something I've been working on. I built my own Magnehelic (thanks to PiedPiper who gave me plans). It still needs to be calibrated (I've been using the school's), but it's still cool. Needless to say you can't buy one like this. All the lights even come on and the gears move and it plays music. 8)

Image

Image

mirwa
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Re: Bent pad cup

Post by mirwa »

Dont ever stress about a key or piece of metal being bent so many times that it snaps, it really is a misnomer in instrument repairs.

Out of say 10,000 instruments plus, not one has ever broken on me, and every single one of them has been bent back into shape.

Yes you can overwork a piece of brass when hammering dents etc and fracture but that is a different scenario than bending a key, as you are actually hardening the material by the hammering, the only way to remove the induced hardness is to anneal

With bending, you have an elastic point and a plastic point, the elastic point is where the material has been bent but still occupies the same space, it is no thinner or thicker than previously just simply bent, this in no way harms the metal, the plastic point is when it has been bent to such a degree that it has started to thin out , it no longer can occupy the same space.

Plastic point bad, elastic point good :)

Steve

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pied_piper
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Re: Bent pad cup

Post by pied_piper »

@ fg18: Cool! That's the first time I've seen a steampunk Magnehelic... :shock:
"Never give a flute player a screwdriver."
--anonymous--

fluteguy18
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Joined: Sun Jul 16, 2006 3:11 pm

Re: Bent pad cup

Post by fluteguy18 »

Lol! I think it's cool! My workbench is ridiculous! I've stained and carved all the handles on my hammers/mallets, I have a tool post made out of a solid slab of walnut, I have an old looking mini crate holding my needle oilers (with apothecary style labels), an old looking little jewelry box holding my razor blades, all sorts of apothecary bottles and vials everywhere, and my screwboards... very special. Stained and lacquered and gilded wood with antiqued paper decoupaged on top. Calligraphy writing with hot air balloons and dirigibles painted on them with gears and pocket watches, and all sorts of stuff attached to them. I have a just a regular occulus style jeweler's loupe and then the old style that clip onto my glasses with multiple lenses, and a big old magnifying glass, and I've engraved some of my metal tools and ... yeah...

My bench is cool. 8)

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pied_piper
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Location: Virginia

Re: Bent pad cup

Post by pied_piper »

fluteguy18 wrote:My bench is cool. 8)
Pictures? I've seen a few teasers on your blog, but more would be good...
"Never give a flute player a screwdriver."
--anonymous--

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flutego12
Posts: 554
Joined: Mon Apr 02, 2012 2:51 am
Location: Southern Hemisphere, Earth

Re: Bent pad cups and maghelic machineds

Post by flutego12 »

greetings to my three good friends on flutelund (+Zevang of course)

so glad somebody has broached this topic and sparked some debate.
flutist with a screwdriver

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