45 replies to this topic

[JimLucas]

I don't understand a word of what you mean..."massive"...???

Sorry if I was unclear. I didn't mean "more massive" in the colloquial sense of "larger", but in the physics sense of "having greater mass". A 4 g object is twice as massive as a 2 g one.

The *weight* = *mass* of the button in this case is the same thing...or is it not??

Technically, it is not. Weight is proportional to mass, but not identical to it. Weight is force; force is mass times acceleration; weight is mass times gravitational acceleration. Gravity on Mars is about 1/4 what it is on Earth, so any object would weigh only 1/4 as much, and you could lift 4 times as much mass. But if you were pushing something sideways, you could only move about the same mass, not 4 times as much, because you would be overcoming the same inertia.

"Massive"..you evidently mean 'density'...

No I don't. Mass = density x volume. Change either volume or density, and you change the mass. Larger buttons of the same density are more massive. So are buttons of the same size, but made of a denser material.

...if the density is higher for the same mass you likely get a 'smaller' button....

And if the density is higher for the same size button, it has more mass.

[Paul Groff]

Ed

Believe I did mention an interaction between springing and button weight. But, *if I understand you properly* it is not as simple as you suggest. Rarely will the dead weight of the button be acting against the spring pressure that keeps the pad down. When the button is not being played, I would think most of the button's weight would be borne by the bushing and the lever. My physics is nearly forgotten, but I want to say that the spring acts against the momentum imparted to the button by the finger. Maybe "pressure" is more appropriate than "momentum" but I think velocity is involved as well as force. Anyway, even if my physics needs to be corrected, I have a lot practical experience making these work, and this is my perception. For proper, quick action (even for a very light touch) I require a spring much heavier than needed just to keep the valve closed against whatever vector of the button weight bears against the spring when the button is at rest. Some of the Praed St.-stamped Jeffries I mentioned, with very heavy buttons, have very fast but still featherlight springing with nary a pad-leak on the press, even if you squeeze a little with no buttons down.

Very wide buttons can be used with no sticking, if the instrument is in proper order. I'm sure the Dipper you played was out of adjustment. Humidity (too low or too high) can have an effect on the woodwork of ends or bushing boards, through shrinkage, swelling, and/or warping, causing the bushings to pinch the buttons. Corrosion or dirt between button and bushing can also be a problem. Wear or bending to the action, movement of the action board relative to the ends (again, usually due to inappropriate humidity), lever bushings out of position, or even the normal compression of the pads and/or dampers (if not compensated by a shim or an adjustment to the lever) can also cause a malfunction of this type.

However, I agree with you about friction in general and have noticed that wider buttons can be trickier to set up properly. Independent of friction, larger diameter buttons need more attention so they won't jam as the radial movement of the lever meets the (usually) vertically-drilled button holes and guide-pin holes. I think this effect may be due to the length of the lever hole through the button, which is indirectly related to button diameter. I have become very tuned-in to this lately, working on a number of old Jones anglos with very wide (and comfortable!) bone buttons. Even when unbushed, these can be set up to play very smoothly with no sticking and very low spring pressure, if desired. It just takes time, care, and thorough "playing-in" to seek and correct action problems.

Paul

Edited by Paul Groff, 05 January 2004 - 05:26 PM.

[JimLucas]

Weight is defined as "force due to the effect of gravity."
massive buttons contribute to an instrument that might manifest greater inertia in pressing the buttons. But in all cases (except on the moon), they are the same thing.

Any definition of "weight" that doesn't mention "mass" is incomplete, and therefore potentially misleading. Weight is the force resulting from gravitational acceleration acting on a mass. Weight is proportional to mass: You can't have weight without mass, but you can have mass without weight (e.g., in the "weightless" environment of an orbiting space station).

Weight = mass x gravitational field strength.

That's better.

...massive buttons contribute to an instrument that might manifest greater inertia in pressing the buttons.

The inertia is my point, or rather the force needed to overcome the inertia. How large an effect that is compared to spring strength or bushing friction, I don't know. And what proportion of the inertial effect is contributed by even heavy (e.g., solid steel) buttons, as compared to the pads and levers, I don't know. As I thought I said previously, there is definitely an effect due to mass; I just don't know how significant it is.

[JimLucas]

1)  The heavier a button is, the stronger the spring has to be on the concertina action.

The more massive a button is, the stronger the spring must be to return the button to the un-depressed position in the same length of time. With the same spring, a more massive button will take longer to return to the initial position when released.

Without friction, a button 4 times as massive (e.g., made of steel instead of ivory) would take twice as long to return. Double the spring strength, and you're back to the original return time, but you need to press twice as hard to depress the button with the same speed as originally. Adding the effect of friction will slightly change those factors of 2.

It seems to me that one has to be careful here or the valve may not close on the rebound.

Greater button mass will slow it down, but not stop it. If it actually fails to close, that must be due to friction... or an obstruction.

2)  The  larger the button's diameter, the greater the friction will be between button and felt.

That's due to the larger area of contact between the button and the bushing, but factors affecting the coefficient of friction -- notably tightness of fit -- are at least as significant.

...I have played a large buttoned dipper that sticks a bit because the buttons are too wide.

If they stick, it's almost certainly because they fit too tightly into the bushed holes. Compressing the bushing felt might alleviate the problem.

[Paul Groff]

Jim

I like your reply to Ed's first point (better than mine). There's a lot to think about here. I think Rich's point in an earlier topic that button pressure and pad down-pressure can be varied somewhat independently is related to these issues also.

How much of this theory did the Victorian (and later) makers know, or was the development mostly trial and error? I love the concertinas they made. The good ones (of many different button materials, dimensions, and spring pressures) really are fast and comfortable, when they're set up well, aren't they? I have seen successful solutions with solid metal, hollow metal, metal-capped wood, metal-capped plastic, and bone and if the QUALITY of construction and restoration are both high, all work great.

Paul

P. S. I thought John Connor in Essex used solid stainless steel for buttons.

Edited by Paul Groff, 05 January 2004 - 04:33 PM.

[JimLucas]

I thought John Connor in Essex used solid stainless steel for buttons.

Hmm. His instruments have a reputation of being heavy. Cause and effect... or just coincidence?

[Bob Joyce]

Any reason why you can't create new buttons from bone?
Bob

[goran rahm]

Ed:"1) The heavier a button is, the stronger the spring has to be on the concertina action. It seems to me that one has to be careful here or the valve may not close on the rebound."

Goran:Yes, of course..but it will be significant only at high speed as I mentioned so again...the matter of button *mass* may be of importance if/when a major aim is best possible finger articulation staccatto and presto...
The varitations don't have to be so wide however and compensation may be possible.I mentioned elsewhere for example that by using 7mm tops instead of 5mm ones the pressure at the tops is reduced to half.

Ed:"2) The larger the button's diameter, the greater the friction will be between button and felt. Not to malign Colin Dipper in any way, but I have played a large buttoned dipper that sticks a bit because the buttons are too wide."

Goran:1)If it sticks it may be due not only to greater friction as such 2) when making buttons in two parts it is very easy to have a wider top than the stem to improve conditions. A metal stem 2mm wide and a cap/top 7-10mm wide for instance...

Goran Rahm

Such is life. Ed.

[JimLucas]

Any reason why you can't create new buttons from bone?

In principle, no. I think some restorers may actually do that for individual repairs.

But I would expect the raw material to require more working than metals, plastics, or woods. Those can all be obtained readily and cheaply in various diameters of rod stock. Is bone available in that form? Is there even a commercial source of clean bone of quality adequate for carving?

Boiling your own does have soup broth as a tasty byproduct, but I doubt that benefit offsets the labor involved in the preparation.

[Clive Thorne]

The  larger the button's diameter, the greater the friction will be between button and felt.

Not nessecarily true: In theory the frictional force is a product of the pressure (per unit area), the area and the coeficient of friction. If the area is increases then for the same absolute 'load' the pressure (load/area) reduces by the same amount. I.e total frictional force is unchanged. This assumes of course that the load does not cause major deformation of the surface.

If the bushing is there to support the button during use then a larger button will not need to be preloaded (ie packed as tightly) as much as a smaller button to give the same lateral support.

Clive.

Edited by Clive Thorne, 06 January 2004 - 12:03 PM.

[Paul Groff]

Clive

Excellent point. Might this be why (just as an empirical observation) I seem not to mind the lack of bushings as much when button diameter is greater?

Of course, bushings also prevent wear, especially important with bone buttons rubbing against wooden ends (or metal, if the holes in the bushing board and metal ends are not perfectly aligned). But your point (that the bushing can fit the button more loosely with a larger diameter button and still do its job?) will be useful to remember. I have to admit, I just adjust them (tighter or looser) until they work well!

Paul

[JimLucas]

...the spring acts against the momentum imparted to the button by the finger. Maybe "pressure" is more appropriate than "momentum" but I think velocity is involved as well as force. Anyway, even if my physics needs to be corrected,...

It does.

The spring acts against the force of the finger on the button. The button's momentum is a side effect, not causative. (Momentum is the integral of the net force over time.)

Pressure is also a secondary factor. The finger's pressure is the force divided by the surface area of the end of the button. A button with larger diameter will experience less pressure for the same force, but to depress it against the same spring, the same force will be needed, not the same pressure.

Velocity, too, is a result, not a cause, though it may also appear as a "requirement", since depressing a button more quickly requires a higher average velocity. But once again, this is obtained by the finger exerting greater force. Forces are the fundamental factors: the force of the spring, the force of the finger, the force needed to overcome inertia.

Weight is also a force, but it's not really involved if you're pushing a button sideways. In fact, if you hold a concertina with the bellows vertical, the force required to press the buttons on the upper end will be less -- by the *weight* of the button, less an effect in the opposite direction due to the weight of the pad at the other end of the lever -- than that needed if the instrument were horizontal, and the force required for the buttons on the lower end will be greater by the same amount. You can probably ignore that amount, though, since it must be significantly less than the force required to depress the button in any orientation, or the pads on the one end would be in danger of falling open spontaneously if/when the instrument is held vertically.

I have a lot practical experience making these work,...

IMO, that's worth more than a mass of physical theory, right or wrong.

[Paul Groff]

Jim,

Thank you for helping sort these terms out. It is confusing because we use "pressure," "force," etc. in less precise ways in ordinary language -- but the whole point of physical analysis must be to make more precise our understanding of what's going on. This can only help with the practical work -- and maybe suggest some new solutions to problems, and new ideas for design and materials.

Paul

[JimLucas]

Thank you for helping sort these terms out.

Well, I need to make some use of those years I spent as a physics major.

[Clive Thorne]

I have to admit, I just adjust them (tighter or looser) until they work well!

Which is exactly as it should be!.

It may be interesting, even useful, to know the theory sometimes, but at the end of the day its what works that is important, and the human repairing/building/playing the instrument is the best judge of that.

Clive.

[goran rahm]

Good!...so what is the ideal button made of and what does it look like?

Goran

[JimLucas]

...what is the ideal button made of and what does it look like?

The ideal button for you, for me, Alex, or for Rhomylly?

[JimLucas]

...what is the ideal button made of and what does it look like?

Alternate response:

Red, white, and blue enamel on thin metal; it says "I LIKE IKE".