Discussions > Instrument Design, Construction and Repair
Adding Stops/Couplers et al
Gena Crisman:
Hello, as per the title, I'm curious about Stops and Couplers, so, after searching around for a few days and finding little functional information, I've made a post. A lot of information I have has been gleaned from pictures, in particular those that were shared in this thread, this post specifically.
I imagine we're all familiar with the external function of registers/stops; you push a button or move a plunger up/down and it turns off some of the reeds in the instrument.
Usually a slide with holes/blocked off areas moves in and out of alignment with holes in the fondo/reed block. Sometimes this is moved manually, with a direct physical connection, or mechanically, with springs and levers (I guess?)
However, this means that the part of the mechanism that you interact with is on the 'outside' of the instrument, and the part that stops the reeds from playing is on the 'inside' of the instrument. This means the mechanical connection must travel through the barrier separating the two sides.
So uh, I guess how does that work? Are the holes just a really tight tolerance? Are there any particular things one is supposed to do to mitigate issues in that regard?
I'm also quite unsure the mechanics of how mechanical coupler switches actually work, and am very interested in reading more about them. However, I have no leads on what the school of engineering related to it would be called to search out more information.
I ask because a) I'm inquisitive and b) I'm considering my options for adding a Thirds stop to a Black Pearl 2 that I own. First concern: The thirds do seemingly all share plates with one another, so a stop slide should be fine on that front. Second concern: because of the giant fundamental reed block next to it, there should be plenty of clearance to do things underneath the chord reed block that might raise it up, as there's no chance of the melody and bass chord blocks touching one another. Other instruments may have issues.
I believe that, principally, the standard process would be to
1) Remove the existing padding from the fondo
2) Create a sandwich of thin pieces of wood or metal, with a slidable filling, to prevent direct pressure from the block (once secured) on the slide
3) Restore the reed block mounting points (presumably a very fiddly step)
4) Put a new layer of padding on the top of the sandwich
5) Mechanically link the slide to an external plunger, which will involve putting a hole in the case and probably removing part of the bellows frame end so that there's space for that.
6) (I presume) fine tune the reeds as they'll have been pushed 1-2 mm farther away by the slide mechanism
7) ????
Are there other concerns of which I am not aware? It sounds quite involved but not implausible as something a dedicated individual could do themselves. I have other... strange ideas, but, I think I should first try to understand the reality of how existing solutions would work, and ideally test on an instrument that isn't my main instrument.
Theo:
Adding a thirds stop can be even simpler. (1) no need to remove the gasket (padding) (2) no need to make a sandwich, just one layer works well. thats how most Italin made thirds stop work.
Other things to check"
(1) all the thirds reed plates are on one side of the block, move them if not.
(2) the reed plates are spaced far enough apart so that the sliding register plate can park the holes in between the reed vents.
Gena Crisman:
Well, that's interesting information! Just having the slide held in place by the reed block would be simpler. However, well, I'll attach a photo and see if that works (if not, it can be found here) - attached ought to be a photo of the present state of the bass end.
The thirds are all on the one side, the side with the 4 holes (it seems anyway) - they're the top side as viewed of the trio of air holes, so, there doesn't appear to be any obvious issue there which would require them to be moved. Also, there is clearly plenty of space for the parking of said holes, so, those (very valid) concerns are alleviated in this case. I am kind of surprised that that is the situation, but, there you go.
But, so, you'll have to help me a little here. When you say there's no need to remove the gasket, are we saying one could build a slide mechanism floating on top of the gasket, effectively placing the physical slide on the reed block side of the equation, but, just clamped in place via the reed block fixing down mechanism? That would be much simpler, but... I haven't seen that. I guess I got stuck thinking the gasket would have to be in a particular place but... there's really no reason for that to be the case I suppose, it just needs to be part of the clamping mechanism and anything that will transfer the pressure could be added in between the block and the gasket, right?
When you say one layer, do you mean, no static flat plate of 'bread' at all? Or, just 1 'slice', ie, Fondo, Gasket, Bread, Slider/Filling, Reed block? I.. should probably draw a diagram at this point.
I should also ask, are there material concerns such as friction etc? I've seen both wood and metal slides. Presumably friction is both bad (hard to move) and good (stays in place). I've heard of magnets to help a low friction slide stay in place but, I'm not sure how to avoid having a high friction slide.
Theo:
Your reedblock looks ok for fitting a slide. The slide does indeed just run directly between the base of the block and the gasket. When these are factory fitted the block has a shallow channel routed into the lower face of the block. When retro-fitting you can glue the same material on either side to form a channel. I’ve usually used 1mm aircraft ply to make the slide.
rees:
I've retro fitted a thirds stop to many Italian boxes. I always rout a 1.5mm deep channel in the reedblock then make a 1.5mm plywood slide to fit.
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