Minimeca24

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Minimeca24 as said in its name is a very little 24 notes keyed reed organette.

But it is also a simplified instrument in which only the useful things were kept. Undoubtedly, it had an effect on aesthetic aspects, but neither on the musical qualities, nor on the reliability.

A 24 notes keyed instrument ?

I had a set of 27 already cut accordion reeds left. Why shouldn't I build a little instrument with them?

A keyed instrument : For many years, I dreamed to build a keyed organ according to my own approach, since in the principle, it may be very simple (look at the Ariston...).

The Thibouville 24 notes scale : I had to chose a keyed scale at least for the available music. And I remarked that transposing the Thibouville original scale by 2 semi-tones, the resulting scale was included in my available set of reeds. Isn't it fantastic?

Oh yes! I bought nearly nothing, and I built it only from junk things available at the moment in my shop. Then don't ask yourself too many questions concerning some material choices or sizes: I used what I had...

How does it work...?

The base is a "spring-key". The cardboard keeps it down, while a little spring keeps the pallet closed. As soon a hole appears the key goes up, and, since its spring is stronger than the one of the pallet, this one goes opened.

Working principle... Nothing complicated!

To be clear, it must be said that the strength which opens the pallet, is equal to the difference between the one of the 2 springs, added to the pressure of the air running through the reed. If all is identical elsewhere, the more the reed is large, the more the pallet offers an important area to the air flow, and then, the more it opens. That's exactly what we need!

Building it...

In the order that I made them (from inside to outside), I will present: the reeds chest, the case, the air system, and the mechanical part.

All along this project, I tried to accumulate all the time that I spent, excepted when it failed. Of course, it mostly depends on the way that one can work, and of the tools that one can use, but I am often asked this question. Well... It gives an idea.

The reeds chest (Accumulated time: 17 hours)

The heart of the instrument....

The little hole on the valve was for an action hook. But I did it in another way...

The spring loop is shaped around a 4.5 mm drilling bit

The key's tails are inserted in a sole piece of wood. The full block in screwed behind the valves assembly, while the key's beaks are inserted in a U-shaped steel ring glued at the end of the pallet. A little felt damper glued in the U-ring, prevents the clicking noise metal over metal when a key moves up.

The damper is made of piano keys felt.

Remarks : 
1. The global shape of the keys, their size, and the different angles were not made randomly! I experienced several models before keeping this one.

2. Don't try to see something new in this system. In fact, it is nothing more than 2 springs working in the opposite way as well as the "compensated levers system" from Thibouville. The main objective being to reduce the constraints on the cardboard. To make simple, let's say that I only removed all the levers between the springs ;o)

The scale : 

C, D, F, G,
C, D, E, F, F#, G, A, A#, B,
C, D, E, F, F#, G, A, A#, B,
C, D

Not visible on the picture: there is a thin paper strip on each side to prevent air leaks

That's it. The most difficult is done. The "only" thing left is to put wind underneath, and to make perforated carton sheets slide over it. And sure that it will make music!

The box (Time spent : 5 hours)

It also has the cardboard way function. Putting 155 mm between sides will allow an easy sliding of the 154 mm width books. It is fully made of 10 mm plywood.

The gaskets are in situation. The screw on th right picture opens the reservoir valve

The big rectangular notches at the top left will receive the mechanical part. The box is presented here in a finished state, but it should be noticed that both ends were definitively glued, only after setting the height of the cardboard way.  

The air system (Time spent: 11 hours)

It is made of a double effect 140 mm width bellow, and a little reservoir. All the wood pieces are varnished. The covering is principally made of cardboard in flat areas and thin leather in the folds. Cardboard is glued on leather with PVA while leather is glued on wood using hot hide glue.

The full wind assembly. I find it very nice ;o)

For such a little bellow, this technique doesn't save much leather. But for a bigger one, it should be more important. Anyway, it gave me a chance to use leather leftovers, and... I wanted to try this.

Cardboard driving (Time spent: 21 hours)

No pulley, no belt. The throw of the crankshaft is simply screwed on the drive roller which is rubberized with Sikaflex (any other solution suitable). The upper pressure roller is a smooth steel rod while the keys roller is made of a smaller one, with spacers and washers. All these rollers are running on nylon bearings.

Throw distance to drive roller (between axis)  : 22 mm
Drive roller diameter (including rubber) : 12 mm
Upper pressure roller (polished steel) : 12 mm
Keys roller : 6 mm rod, spacers (pipe segments), and 1.5 x 6 x 18 mm washers. Washers are free and the spacers only are glued on the rod.

The whole assembly is screwed with 4 long wood screws

The keys lowering cam is made from a flat piece of steel.

The cam : a bit of lathe work

Now, the remaining question is:  How is it possible to align all this stuff and to make things work together?

Ok. I explain...

The top side of the spacer between the bottom parts of the mechanical assembly will be called the reference plane (plan de référence on the picture)

1. First thing is to put in place the full reeds chest with its keys. The spring effect of the keys will pull the pallets up by about 3 mm. As long as we don't obtain these 3 mm all over the pallets it's no worth going ahead. It is possible to reach that by slightly bending the key's tail as necessary.

2. Then, put in place the lowering cam in such a way that in the low position, all the keys are leaving the felt damper by about 1 mm down. It is necessary to work precisely when drilling the cam's end bearing. If necessary, it may be adjusted by putting a sheet of cardboard under the chest. It is what I did.

Keys up and keys down. See the 1 mm space

3. With the lower part of the mechanical assembly in place (bottom of drive roller bearings + spacer), bring the reference plane at the level of the lowered keys.  It may be done, either by filing the bottom of the bearings underneath if the keys are too high, or by putting thin wedges under them to get the keys higher.

A little ruler allows to check the exact matching of the reference plane and the top of the keys

4. Then the key grid is glued in a rebate at the end of the incoming table on one side, and screwed in another rebate in the spacer on the other side.

Keys down: nothing above the grid.

5. The last thing to do is to put the incoming and outcoming tables right in the same plane, by setting the height of both end pannels of the box.

At the end of this step we are sure that when the keys are lowered at the grid level, the pallets are all closed. And when one key goes up, the corresponding pallet opens by 3 mm.

Toe-piece story and “clac-clac” story...
The key move is limited to less than 4 mm by the lowering cam itself when this one is in the key-up position. In order to reduce the metal over metal noise, a leather strip is glued on the lower side of the cam.

The cam and its leather strip

That's it! Now, it's just time to read the first carton :o)

Ready to work key system

Settings (Time spent : about 3 hours)

If all the keys are identical, there is nearly nothing to adjust. The pallets must be closed when the keys are at the grid level. Individual adjustments may also be performed by slightly bending the U-rings of the pallets. That's the reason of their shape. 

All the reeds have also been tuned at this moment.

Decoratings (Time spent : 5 or 6 hours)

I still had a leftover of that green painting left. Now the pot is empty! The overall dimensions are (without crank): 35 cm width, 22 cm height, 18 cm depth and the weight is 3 kg.

I promise that next time, I will try to imagine another decorating !

To make simple, the crankshaft and its connecting rod are left visible on the front (by the way, there is also a crank on the other side! ;o)). But of course, it should be possible to attach a front panel which would cover them.

Music

An old traditional popular French song. A light clicking may sometimes be heard. Actually not around the lowering cam. In long bass notes, it may happen that the beak of the keys strikes the spacers of the keys roller. I should have used larger washers to make deeper slots... But anyway, it doesn't mind a lot.

Le dénicheur.mp3 (2Mo)

Some figures...  

These data missed to me at the beginning of the project. Here they are, measured on the finished instrument.

Sketches

I am far to be a design draughtsman. Then I didn't dare to call it a plan! In this document, I gathered all the sketches and information which might be useful to build this instrument. Document translated in english, but still in metrics units.

It is a unique pdf file which contains 4 pages. Printing it at scale 1 in A4 size, you'll get four paper sheets that you can put together to obtain an A2 drawing at scale 1.

Total ammount of time spent : about 63 hours. And may be as much in trials, failings, drawings, and... to compose this page! ;o)