Camera type of bellows usable in concertinas?

[RAc]

Hi there,

 

while browsing for bellows making, I came across a number of vids that show how to make bellows with alternating valleys and peaks in the same plane, such as this one:

 

Although this style appears to be mostly used for camera bellows, some videos suggest that it also works well for air pumping applications.

 

Has anyone here experimented with this type of bellows fold architecture for concertinas, and if yes, with what results?

 

Thanks!

 

Edit: Although square bellows are the easiest to fold this way, it should also possible to make hexagonal or octagonal bellows this way (although then we would naturally be back to gussets).

Edited March 18 by RAc

[Ken_Coles]

Years ago at the Northeast Squeeze In (in the Bucksteep days) Bob Snope did a workshop (I was not able to attend) where everyone made bellows that came out square like this. I remember hearing talk of how it was done (cracker/biscuit boxes?). Thin pieces (of wood?) were mounted on each end. One end had a hole you covered with a finger and opened for air, on the other you mounted a single accordion reed plate over an appropriately-sized hole. The reed plate had two notes (e.g. G and A). Someone used his at the talent show that evening to play "I am the very model of a modern major general." Maybe someone here was at that workshop and can tell us more, and more accurately - I'm hazy on all the details and may have some of them wrong.

 

Ken

[Shuenhoy]

It looks similar to this one.

 

Edited March 18 by Shuenhoy

[Steve Schulteis]

I've experimented with this a bit. You can actually fold a hexagonal version of the same thing, the angles are just different.

 

Lacking proper gussets, the corners have to give and shift (when made from paper, they suffer significant wear). Otherwise expanding the bellows would just unfold the sheet. I think cameras avoid problems by just having a lot of folds and a more limited range of motion in order to reduce the amount any individual fold has to move. The fact that they aren't pressurized and don't need a particularly sturdy bellows structure also helps. This construction method doesn't lend itself very well to reinforcement with cards.

 

Another issue is joining the bellows to a frame. With a traditional concertina bellows, the neutral part of the fold where the bellows "radius" doesn't change is the top/outside edge, and this is where it joins the rigid frame. With this folded style of construction, the neutral point is halfway between the top and bottom of the fold. Of course, if you join to the frame at this point, the bellows has to stick out significantly more than the frame, which is undesirable. I guess you could also attach the frames differently, as in the video above, but that produces a bulky frame instead.

 

In the end, I decided the Flying Duck construction method just made more sense as a low-effort solution.

[RAc]

11 hours ago, Shuenhoy said:

It looks similar to this one.

 

Thanks, but actually no - in Tiposx's construction, all the valleys and peaks are still in the same plane which is exactly what the camera type is not... in fact, it was that very thread that tipped me off to look into bellows architectures more - I just ordered a batch of Porcher Skytek which is paragliders cloth and hope to begin work on my bellows soon.

 

[RAc]

7 hours ago, Steve Schulteis said:

I've experimented with this a bit. You can actually fold a hexagonal version of the same thing, the angles are just different.

 

Lacking proper gussets, the corners have to give and shift (when made from paper, they suffer significant wear). Otherwise expanding the bellows would just unfold the sheet. I think cameras avoid problems by just having a lot of folds and a more limited range of motion in order to reduce the amount any individual fold has to move. The fact that they aren't pressurized and don't need a particularly sturdy bellows structure also helps. This construction method doesn't lend itself very well to reinforcement with cards.

 

Another issue is joining the bellows to a frame. With a traditional concertina bellows, the neutral part of the fold where the bellows "radius" doesn't change is the top/outside edge, and this is where it joins the rigid frame. With this folded style of construction, the neutral point is halfway between the top and bottom of the fold. Of course, if you join to the frame at this point, the bellows has to stick out significantly more than the frame, which is undesirable. I guess you could also attach the frames differently, as in the video above, but that produces a bulky frame instead.

 

In the end, I decided the Flying Duck construction method just made more sense as a low-effort solution.

Thanks, Steve, very valuable and right on-the-spot (to be expected; ;-)) . I agree about the tension in the corners where the valleys and peaks meet. There is one video, however, in which all the card are spaced apart from each other about 2mms, and the carrier cloth is full face laminated to the entire assembly, so if the cloth is strong and sturdy by itself, the underlying "card skeleton" can provide the shape while the cloth can provide the flexibility and take the tension.

 

If I have some time at hand, I'll experiment with this idea, but as with almost everything in concertinas, the reasons why the instruments are built like they are probably good reasons and the result of a long trial-an-error process, otherwise something else would have prevailed. So for the project at hand, I will likely stick with the traditional way (albeit try to replace the leather with something else, not for veganism reasons but because I am not a good skiver).

Edited March 19 by RAc

[Steve Schulteis]

2 hours ago, RAc said:

I agree about the tension in the corners where the valleys and peaks meet. There is one video, however, in which all the card are spaced apart from each other about 2mms, and the carrier cloth is full face laminated to the entire assembly, so if the cloth is strong and sturdy by itself, the underlying "card skeleton" can provide the shape while the cloth can provide the flexibility and take the tension.

 

That will work, but you'll be trading travel distance against bellows structure. I don't know if you'll find a good balance or not - I didn't investigate that detail very far. I'm definitely interested in seeing that video if you don't mind sharing the link.

 

One thing you might try is spacing just the corners, like this (cut along red lines to create the space):

 

2 hours ago, RAc said:

If I have some time at hand, I'll experiment with this idea, but as with almost everything in concertinas, the reasons why the instruments are built like they are probably good reasons and the result of a long trial-an-error process, otherwise something else would have prevailed. So for the project at hand, I will likely stick with the traditional way (albeit try to replace the leather with something else, not for veganism reasons but because I am not a good skiver).

 

Given that bellows are still a relatively high-skill, labor-intensive thing to produce, I think there's a great deal of value in exploring more accessible/affordable approaches to their construction. And we have all kinds of crazy materials and tools that didn't exists 100+ years ago.

[RAc]

9 hours ago, Steve Schulteis said:

I'm definitely interested in seeing that video if you don't mind sharing the link.

Hi Steve, that would be this here one:

 

 

He uses stripes of tape to skin up the skeleton with, but I'm sure there is a workflow to do that with a solid surface of cloth (eg thermoplastic fabric and an iron).

 

Edited March 19 by RAc

[Steve Schulteis]

Neat. The staged tape assembly method is clever. It looks like he's using a card stock that's a lot more flexible than anything I've used for bellows cards, which is probably part of why it works with the small gaps he's using. I wonder how it would hold up for a concertina. He ends up with a springier bellows than I'd like for my purposes, but some of that is probably solved by replacing the tape with a more flexible material and some can probably be eliminated by using wider gaps at the corners.

 

I dug up some photos from one of my experiments. The corner gaps here were far too small for the rigid cardboard I used, and the resulting bellows was extremely stiff, to the point of tearing itself apart.

 

[Steve Schulteis]

After rolling the geometry around in my head again, I think the correct corner relief would actually look more like this:

[RAc]

24 minutes ago, Steve Schulteis said:

It looks like he's using a card stock that's a lot more flexible than anything I've used for bellows cards, which is probably part of why it works with the small gaps he's using.

Hi Steve, he mentions the cardboard strength @ 1:38. If I hear it right he says it's 230 gsm. The board I plan on using is 300gsm (the thickness I have used before). If I remember a previous conversation on the issue in this forum correctly, yours is laminated from 2 inner layers of 300 and two outer layers of around 100, adding up to 800, right? That is very stiff...

[Steve Schulteis]

6 minutes ago, RAc said:

If I remember a previous conversation on the issue in this forum correctly, yours is laminated from 2 inner layers of 300 and two outer layers of around 100, adding up to 800, right? That is very stiff...

 

I tested something like that, I don't remember exactly. That was for a traditional build and was based on what Alex Holden has used in some of his work. For my budget bellows I'm currently using 2-ply museum board, which is on the lighter end of what you usually see in traditional bellows construction (at least as far as I can tell), but still much stiffer than 300gsm card stock.

[Julian Macdonald]

@Steve Schulteis "Given that bellows are still a relatively high-skill, labor-intensive thing to produce, I think there's a great deal of value in exploring more accessible/affordable approaches to their construction. And we have all kinds of crazy materials and tools that didn't exists 100+ years ago."

Here's an idea that I haven't tried to build yet but happy to throw into the mix:

Use airtight fabric of the sort used in foot pumps, bagpipe bags  and suchlike

Of course a simple tube of fabric would be far too floppy. So:

- Attach to the ends  some plates that are somewhat wider than the concertina, that is they make flanges extending outwards far enough so that the springs noted below don't touch the bellows.

- Attach between the plates a number of helical springs of a suitable length and stiffness to provide the resistance you want.

Issues: 

- With a normal bellows you want the force needed per unit of extension/compression to be as low as possible for most of the travel. I imagine it would be hard to find a helical spring with that property (or indeed impossible? as per Hooke's law of spring extension)

-  So maybe instead use trips of very bendable plastic like that used for cable ties? They spring outward as you close the bellows.

- You won't be playing with an end on your knee.

 

 

 

 

 

[RAc]

Thanks for the input, Julian, this is a fun brainstorm!

 

I had a similar idea but abandoned it for several reasons - first of all (similar to Steve's reasoning about the camera bellows idea) a helical spring has some kind of attachment point to the frame which introduces an asymmetry in force. Second, regardless of which cloth you use, it has some flexibility, yet I believe that some stiffness is required in the assembly to quickly (!) build up pressure.

 

My current idea is this - see attached sketch - this of course is a sideways view. I would 3D print some hexagonally shaped "ribs" that match the shape of the frame. The ribs would be spaced from each other twice the depth fold and eventually make up the peaks of the bellows. The cloth (red) would be fully stretched while being glued to the ribs (figure 1).

 

In the second step (figure 2), the valleys would be made using some kind of elastic band marked blue (first approximation unshaped rubber band, second approximation hollow carbon rods shaping the hexagon  - these can be bought from kite supplies stores - with rubber string threaded through it).

 

I have a suspicion that with this construction, my second counter argument would still hold - namely that the bellows would probably work this way, but not very fast - the cloth, even though air tight, would first blow up before building up internal pressure.

 

In that case, it is still possible to reinforce the "trapezoids" with card stock glued in from the inside, introducing stiffness. What we would end up with then is a lot like a traditional bellows but made from one contiguous piece of cloth where the runs and gussets do not need to be applied individually (so it would not be a skeleton with the air tight compenents built around it but conversely with the skeleton built into the single airtight component, does that make sense?).

 

Most of that idea crucially depends on how well the cloth accepts being glued to both plastic (frame and ribs) and paper/wood (inner reinforcements if needed). That is something I plan on experimenting with as soon as I get the fabric. The product description mentions that it is thermoplastic, so possibly it can be ironed onto at least the frame and ribs which would be ideal.
 

Edited March 20 by RAc

[Owen Anderson]

To prevent the material from "blowing out" on compression, you might want to look into low-creep materials. UHMWPE, commonly branded as Dyneema or Spectra, is used for the sails of racing yachts, and has exactly the kind of very lower stretch properties that might suit here. It will have some construction creep from the weave itself, but that can be pre-stretched out.

[Don Taylor]

Just a suggestion:

 

Make some (very) leaky but nice looking fake bellows for the cosmetic effect but inside have an air-tight industrial rubber bellows with your sensors inside:

 

Jim MacArthur made a midi EC using some rectangular rubber bellows about 10 years ago, I don't recall him saying the bellows were a problem.

 

Here are some pics of Jim's midi concertinas along with a warning about the future of midi concertinas...

 

And here is a link to one of Jim's earlier posts with some details about his bellows: 

I think that these might be the bellows he used (the part number is a little different):

https://www.mcmaster.com/9742K34/

 

McMaster has other sizes of the same type of bellows:

https://www.mcmaster.com/products/bellows/rectangular-bellows~~/

Edited March 20 by Don Taylor

[JimMacArthur]

Hi gang!  I took a decade off, but Don dragged me back.  Most industrial bellows have a pretty horrible feel, _but_ I found that bellows made of rubber-coated fabric (as opposed to pure rubber) aren't too bad.  Don's McMaster P/N (9742K34) is one of those: a square bellows in "rubber-coated polyester fabric".  My exact bellows was the smaller 9742K32.  I didn't find a bellows with a more traditional (hexagonal, octagonal, or even circular) profile, so I ended up back-designing the concertina body around the square profile. 

All of which is to say that it is possible to make an industrial bellows work, but you will be limited in your selection.  You should restrict your search to rubber-coated fabric designs.  And Don's idea of hiding an ugly industrial bellows inside a fake pretty one might expand your options.

Edited March 20 by JimMacArthur
wrong p/n

[RAc]

Hi, just a short update: I have designed the ribs (see attached picture). The tiny cylinders on the inside of each face of the hexagon are attachments to the jig used to keep everything aligned while assembling the bellows. The thinner hexagon extension is a groove; I will order a batch of 10 of these that are all printed in one go (much cheaper and more efficient than printing 10 individually). The groove resulting from printing each pair of two right on top of each other will be the separation line.

 

I have also received the cloth I ordered. It is diamond ripstop nylon, and I am currently conducting glue tests.