Effect of clevis/flexure height on adjustor sway

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Effect of clevis/flexure height on adjustor sway

Postby TerryMcGee on Wed Jun 12, 2013 3:55 am

An interesting topic to stimulate our grey matter. It has puzzled me for a while that the adjuster steady (the bar above the clavier that guides the adjusters) at Canberra sways a lot during playing. I looked into it while up there recently. What I noticed is that the adjustors didn't just bob up and down as expected, but also swayed forward and backward, towards and away from the player, as the batons were depressed. I suspect it's this action that is causing the adjuster steady to do the same.

When I came back, I did some thinking (uh-oh, I can hear you mutter, no good will come of this....). And some drawing. On a CAD package, I set out three straight lines, representing the baton in three locations, one at rest, one at bottom of slot and one halfway (i.e. horizontal). I took the length from pivot to where the adjuster attaches as 12.5", and the angles as +/-2º. As you can see from the image below, if the adjustor were to be connected to the end of this imaginary baton, it would hardly move sideways at all during the baton drop. Zooming the CAD package in, it suggests the total fore & aft movement to be 0.01", giving a movement of +/- 0.005" if perfectly set up.

Adjustor angle.GIF
Adjustor angle.GIF (3.87 KB) Viewed 5478 times


That assumes that the pivot point for the adjuster lies exactly in the middle of the baton, which is probably not common. More common is that there is a clevis attached to the top of the baton, and so the real pivot point is say 1/2" of baton plus maybe an inch to the centre of the clevis, so say 1.5" higher than the centreline of the baton. To simulate the pivoting geometry of such an arrangement, I raised right angles at the end of each of our three baton locations. I used 2" high vertical lines, which is probably somewhat of an exaggeration, but it gives a clearer image. You can now see that the horizontal movement is much exaggerated. Zoomed in, I get 0.14" movement, or +/- 0.07". Not a lot, I know, but 14 times worse! So it seems that there is good reason to have an arrangement where the adjustor pivots from the centre of the baton, not above it.

In Canberra, we have flexures, which are thinned stainless steel strips that are intended to bend, rather than swivel like a clevis. We also have flexible wire cable down-wires, and these are considerably more flexible than the flexures. If we imagine for a moment that the flexures are solid, the vertical lines on my drawing become as long as the flexure plus the adjustor, and so the top end would be whipping backward and forward for many inches, if it were not for the constraint offered by the adjuster steady. So, I suspect what is happening is that the flexures are flexing as little as they can, the cable is flexing a lot, and that the steady bar is moving because it is being pushed by the adjustors trying to move fore and aft.

This probably explains too why we get a lot of clicking noise from the wires where they run through hard plastic grommets in the ceiling register. Instead of just bobbing up and down, they are swinging fore and aft as well.

Much to think about....
TerryMcGee
 
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Re: Effect of clevis/flexure height on adjustor sway

Postby JohnGouwens on Wed Oct 16, 2013 8:29 pm

The first problem is that the adjuster steady isn't fixed in place rigidly. It wouldn't sway at all if it were fixed in place properly. The steadies should then prevent excessive fore-and-aft movement by the adjusters. If in fact the flexures are so rigid that they cause the portion of the adjusters above the steady to move in the opposite direction (meaning that as the key descends the top of the adjuster moves toward the player), then they are simply so stiff that they are creating additional problems with the action. Admittedly, even the best of clevises will have some friction, but that would seem to be the lesser of the evils. A photo of the installation, with one key on the far end depressed would help make what is going on clearer.
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Re: Effect of clevis/flexure height on adjustor sway

Postby TerryMcGee on Fri Oct 18, 2013 6:13 am

Can't do exactly the image you suggested, but this might help illustrate the issue. The front of the clavier is to left of image.

This image shows the baton up with the adjustor disconnected from the flexure and dangling above it:

Flexure alignment with baton up.jpg
Flexure alignment with baton up.jpg (224.89 KB) Viewed 5134 times


(Use the slider at right of image or click on the image to see the lot.)

This image shows exactly the same, but with the baton down:

Flexure alignment with baton down.jpg
Flexure alignment with baton down.jpg (212.32 KB) Viewed 5134 times


What surprised me is just how far out of alignment the top of the flexure and the lower end of the adjustor rod now are. That's what prompted me to do the analysis above. A fraction of a millimetre fore & aft movement at the centre of the baton becomes many millimetres when you come 50mm or so above the top of the baton. It demands a lot of the flexure to bend that far without noticeable side effects.

I also get the impression that perhaps a better location for the flexure could have been found. Notice in the top image, it's clear that the flexure has been bent "backwards" to align with the adjustor top when the baton is up. Perhaps if it had been aligned when the baton was held horizontally, that wouldn't have been necessary and the action would be more centred. Interestingly, there are plugged holes in the batons (just visible as a faded semicircle peeping out from under the back of the flexure base in the "baton down" image) that suggest that was tried.
TerryMcGee
 
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Re: Effect of clevis/flexure height on adjustor sway

Postby JohnGouwens on Sat Nov 02, 2013 8:45 pm

Actually, the plugged holes are more likely from where the base (tongue) part of the original clevis connection went through the key. The flexure connection is surely not the work of Taylor. I assume that is some of Tim Hurd's work. (I do know that some sort of flexure connection was tried at a similar point on the Ottawa carillon in a renovation by Verdin. I don't know of any problems resulting from that, but there have always been noise problems with that console - perhaps to do with the pivot points at the back of the keys? I'm not certain.
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