Author: Matt74
Date: 2017-02-01 03:38
There really isn't any way to calculate pad sizes. I wish there were. The main problem is that the dimensions they give you aren't the ones you want, and all the manufacturers are different. They tell you the outside diameter, but you need the cardboard diameter (hence, the desire to calculate). Then they tell you the overal thickness, but you need the felt thickness. Some manufacturers give a rule of thumb, like subtract .5mm, but it's not always the same rule. Then the step that fits over the cup edge is more or less sharp or curved, which means that you can use a smaller pad when it's curved, and a larger one when it's sharp. Then, especially if it's curved, depending on how thick in needs to be you can use a larger or smaller pad to adjust thickness. There is also preference. If everything is level you can put a larger pad in so that the outer edges come out to the edges of the cup, which looks neat, or have them somewhat inside the edges of the cup, which allows more adjustment. Also, the edges of the pad cups are not necessarily the same thickness. Sorry if that's pedantic, I have a lot of angst about it.
However, I would suggest the following for a spreadsheet:
1. Take thickness into account. Some thicker pads won't fit some places at all. Where they do, for the same cup, you may need a smaller diameter when using thicker pads, and a larger diameter for thinner. (I am told some guys use all thick woven pads on student horns, but I don't know how this is possible - unless they are using smaller diameter pads and/or they're not in straight, or they squish a lot, or something...)
2. I found that the difficult ones are F# ring key, A/D ring key, and 3 ring key, because you have to have the right size for the mechanism to work. The large ones are difficult to seal, but there is more "fudge" room with size.
3. The smaller the key cup, the easier it is to find the right size, because only one or two sizes "fit", and they are easy to level. The larger the key cup the more options you have for sizes. This makes sense because .5 mm (the difference in sizes) is a larger fraction of 9.5mm, than of 16.5mm. For a small one you might be able to use a 9.5 or a 10, and one will definitely fit better than the other. For a large one with an inside diameter of 16mm, you might be able to easily use a 16.5, 17, or 17.5mm.
4. For some keys, you can use a thicker pad to make it "look" right. The LH G#/C# can take a thick pad because venting isn't an issue and it makes the key cup sit tangent to the body.
5. I think pad cups are generally oversized, round down to the nearest 0.5mm. A cup that is nominally 11.5mm will probably measure 11.75, or something like that. It might be easiest to just use an engineer's rule. The cup won't measure exactly the same all the way around, but the 11.75mm shouldn't be smaller than 11.5 anywhere, unless it's bent.
- Matthew Simington
Post Edited (2017-02-01 03:54)
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