Ex-Irvin Marenghi Restoration - some construction questions

Ex-Irvin Marenghi Restoration - some construction questions
Over the last week I have been reading John Page's excellent series of articles on his website regarding his recent restoration of the Ex-Irvin Marenghi organ http://www.johnpage.co.uk/organs/restoration/index.htm. The many photos that he included were so detailed that I realised they could be useful as references for my own organ-building and prompted me to pose some questions about the design, the answers to which I think could be useful for other forum members as well as myself in our future organ-building endeavors. 1) Windchest Internals In the restoration of the windchest of this organ, John recovered the internal space between the 'bars' and the wind-supply space with 'calico' fabric. In a lot of drawings I have seen in books, the space between the bars and the wind space is wood - is there any advantages and disadvantages to using one over the other - it would seem to me that the cloth might wear out - whereas the wood wouldn't - on the other hand, it makes the channels more accessible if they are covered with some kind of removable material. However I could see that you might have a problem with the material that you covered the bars with becoming porous at some point - this won't happen (hopefully !!) with wood. I used CorelDraw to create an image of what I am talking about.

Note that I am not questioning whether John should have used wood or not on this particular project or not - since it was a 'restoration' it is only right to use the original materials etc - but on a new construction windchest, what might be the best option ? Thoughts & discussions welcome. More questions to follow... Stephen

Stephen, Thanks for showing the link to my article. It was intended for this very purpose, in the hope that traditional organ construction will prevail over modern ideas. These old methods have been developed over centuries, and adapted for use in mechanical organs in more recent times. The advantages of calico over wood are: 1. It can be readily removed for repairs and re-sealing of the channels. 2. It weighs less than wood. 3. It is applied far more quickly. 4. If there is a running (bleeding of wind from one channel to the next), or a slight leakage in the pallet, it is a simple matter to pierce a hole in the calico with a screwdriver to relieve the unwanted pressure - the pallet-box is usually short of the full depth of the chest too allow access. This is an age-old remedy, seen in church organ chests during maintenance. The main disadavantage of wood is that if it shrinks it will pull away from the bars and cause leaks. One piece glued over the entire chest, covering all channels may be an option, but if this pulls away from any of the bars runnings will result, with no way to seal them. There _was_ a problem with calico when it was sealed with hot glue, which hardens over time and shrinks, but I use PVA glue mixed with poster paint to show where is has been applied. This never sets rock hard, and allows for movement in the wood of the chest. Normal PVA (not the water-proof variety) can be easily removed in future maintenance. There is no fear of the calico wearing out as it does not come into contact with anything that moves. Your right-hand diagram shows the pallet hinge glued direct to the calico. I have seen this done but much more common is a small fillet piece of wood (about 5mm thick) set between the bars at the hinge point. This provides a firm base on which to glue the pallet and the calico. See http://www.johnpage.co.uk/organs/restoration/chest/23i.jpg Regards, John

Facinating information John; I love the poster paint tip! I've glued wallpaper over channels to cover chests before to seal them but allow for future access (I always screw or pin a light wooden panel such as 3mm ply over the wallpaper to protect it from accidental damage either when storing or fitting inside the organ). You can do this on smaller chests and ventil boxes too Stephen, though I always prefer to make a gasket and screw a wooden covering on, with the covering applying the pressure to the gasket to make the seal (ie no glue at all). This makes removal to access inside straightforward (e.g. a sticking pallet, incorrect pallet pin, broken spring etc), and you can screw it all back up without needing to make a new covering or clean up old glue. It takes longer to make initially, but better in the long run IMO, and with nice brass screws it can look the part too. The idea of perforating a hole in the covering any channels that leak does sound like a little bit of a shortcut to me though - surely this would affect the performance of the channel when it is filled with air to play? (reduced pressure and differing pressure changes at the start and end of the note compaired to the other channels?). All the best, Nick

Hi there Nick With regard to the making of a hole in the cloth of a windchest channel. It may sound drastic, but quite often this is the best option going to keep an organ playing. Picture the scene - the first day at Dorset steam fair, and a customer finds you and asks you to come over because his instrument has a problem. This is not surprising as you know the organ needs work, but the owner cannot afford this at present. You get there to find a main melody note playing away all the time. Not full bore, but enough to be ANNOYING. The push rod is up for that note, so you bite the bullet and open the back of the windchest to find that the pallet is seating OK, but there is a crack opened up right at the back of the wind box. There is no easy way of reaching it, so what are the options. Remove or block up the pipes for that note - and have a note missing for the rest of the rally (sods law states that this will be a main melody note, C or G ). Go back home and collect all your tools, come back, and completely strip out the organ overnight to remove the windchest to glue up the crack. The chest needs a full rebuild anyway, and you are not going to do that overnight! So the best option is to make a small hole in the cloth to counteract the wind leaking in. Slowly increase the hole until the note is not annoying. Hopefully the opening of the pallet will overcome the smal hole to allow the note to play. Not perfectly, but it will sound better than a missing note. This will probably do until the organ can be brought into the workshop at the end of the rally, and a proper job can then be done. It might last to the end of the year, to give the owner time to save up to get the job done properly. I know it sounds a real bodge job, but if it works to keep the thing going, then it is not such a bad thing. Incidentally, you can also use rubberised canvas cloth (american cloth) to do the job instead of calico. The thick cloth has canvas either side with a sandwich of rubber in between. This is airtight, and will glue up a treat as the glue sticks to the canvas rather than the rubber. It is also more pliable then calico, which goes harder when sealed up. Cheers Peter Griffiths

Hi Peter, Many thanks for your reply. I hadn't thought about it like that, and guess under those circumstances it is the best thing one can do to solve the problem 'on site'. Still, if the windchest had been covered in solid wood instead of paper or cloth, as long as one was accurate with lining up the position, surely a small hole could be drilled into the channel with the same effect, assuming the channel was charged with air whist drilling to keep most of the swarf out? I've never had to do this, but thanks for educating me for the future times I might have to. I have used rubberised vinyl cloth before as gaskets though, and it's good stuff as long as you don't put the rubber towards the windchest - I made this mistake on 'Twilight' (screwed on with backing board, not glued) and had bits of the rubber flaking off and coming through the pipes with the air, so started again and used thick Flexoid gasket paper instead which has been perfect. All the best, Nick

Hi there Nick It is fine making a solid wood bottom to a relatively small windchest, but think of an 89 key windchest - about 700 mm wide by 1.8 metres long. The problem is making the bottom of the chest totally flat. If it isn't totally flat, then sealing up the windways to a bottom board becomes a nightmare. Yes, you can pour very runny scotch glue down the pipe holes into the windways to seal between the channels, but how do you know you have done it properly. You can't see inside the thing! You will only find out if there is a leak when all the pipes are on, and it is a bit too late then. Believe me, using calico is the best and most foolproof option for the large windchests. Incidentally, another little tip. Put a little bit of talcum powder on your leather gaskets when screwing them up. In later years you will find that the gasket comes away cleanly, rather than sticking to both surfaces. If the organ gets damp, then the leather can stick to the wood facing, especially as the gasket is screwed down tightly to stop any air leaking. Cheers Peter Griffiths

Many thanks for your detailed reply Peter; I did have smaller constructions in mind with wooden base boards for windchests, but guess when you get to 89 key size chests, calico has to be the way to go. I love the talcum powder tip too, and will try this soon. I tend to use vinyl floor cloth for gaskets nowadays rather than leather; it cuts well (with sissors, knife, bandsaw and can be drilled), can be easily marked out, and is compressable, thus forms a totally airtight seal :D. It does tend to stick on to wooden chest walls when screwed through though, so talc might come to the rescue here! Thanks again, Nick

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