Tuning rig - impact of chamber around reed ?

[Sprunghub]

I am going to build a tuning rig to tune my Crane and hopefully use for any future projects.  I have had a look around and have some idea of how to create something workable but I am uncertain as to the importance - if there is any - of the impact of the air restriction on individual reeds specifically during tuning that the chambers around the reed create in a working instrument? 

 

I can create internal and external chambers if needs be as part of the initial build but most of the examples I can see do not have any ?  Presumably air restriction via the chambers in a working instrument impacts on the speed the reed 'talks' at and the vigour/length of note, which may be irrelevant for tuning purposes.....although getting it going without stalling or weakness may also be advantageous ?

 

 

Edited November 12, 2018 by Sprunghub

[Geoff Wooff]

Yes the chambers  have  an impact  on pitch  but  all you need to do is measure the pitch  of each reed   whilst  they are all still in the instrument... make a chart  of some sorts  to note  each  reed's exact pitch.  Then when each  reed  is on your tuning jig  measure the pitch  again  and tune  the  reed  up or down  by the difference  between the two measurements..

 

Say a reed  is  8  cents  sharp of  your required pitch  when played  IN the instrument  and on the tuning jig  it shows  13 cents sharp  then you need to  flaten the reed  until  your  tuner  reading is  +5 cents.  This should get you very close  to where you want  each note  but   ' some settling of the contents'  is inevitable  and  second and third  checks  on the pitch  of each note  will be needed.

 

 

 

 

 

Edited November 12, 2018 by Geoff Wooff

[Sprunghub]

Thanks for that Geoff......all understood.  

[Chris Ghent]

I have chambers on my tuning device but they do not create a situation similar to being in the instrument.  I still need to do offset tuning. 

[Theo]

I tune reeds in the reed pan placed on top of my tuning bellows, which is mainly designed for tuning accordion reed blocks.   So the reeds are "at home".   I still need to do offset tuning too, so I think it's unavoidable.

[Sprunghub]

Some design feature queries, if I may.......

 

I have started constructing my Tuning Table.  It wasn't going to be an actual table, but I had some spare timber and an idea as to how I might design it, so, a table - of sorts - it is.  I bought a used set of accordion bellows and have routed end plates from 1/2" ply which, now it is fixed and taped/sealed is heavy enough to draw the bellows down.  The table top has a working surface for soldering filing and a slightly larger than bellows sized aperture and the top plate is 1" oversized all around so that the bellows fits into the hole but the top plate sit's on the table.

 

I now need to design the reed holder and 'air hole' and think this set up (image below)  looks very "do-able" given my available kit.   Are there any obvious weaknesses / problems with a simple holder (or holders for different sized reeds  ) as per this design ?  I would probably use slightly thinner wood for the blocks.  Presumably there is no optimum air hole for bellows venting ? just enough to let the air out of the bellows on the push AND be able to be competently valved with 'something' as the bellow falls and pulls through the reed ?

 

[alex_holden]

You can see my holder below, based on the design Crabb used. It's actually a bit too narrow for Jones 'broad' reeds, but works well with Wheatstone/Lachenal/Crabb/Jeffries/Holden reeds. The key thing is that the holder keeps the tip of the reed approximately centred and slightly behind the front of the vent slot. You push the reed frame forward against the tip of the holder while operating the bellows. The tip distance doesn't vary much with pitch, but the width does. The left hand side of the holder is mostly there to hold it in position while you file the tongue.

 

 

The flap valve is very simple, it's a rectangular hole about 20x25mm with a rectangular piece of 3mm plywood over it, hinged on one side with a piece of thin leather.

[Sprunghub]

Thanks Alex.....I have some access to a metal worker.....but no kit/ability myself.  I may be able to something similar with some heavy gauge acrylic.  I can probably work that to create that profile.

 

I think the principal in that wooden rig above is similar.  

[alex_holden]

11 minutes ago, Sprunghub said:

Thanks Alex.....I have some access to a metal worker.....but no kit/ability myself.  I may be able to something similar with some heavy gauge acrylic.  I can probably work that to create that profile.

 

I think the principal in that wooden rig above is similar.  

 

The difference is it's holding the sides rather than the tip of the frame. Higher pitched reeds will go further forward than lower ones, so you'll need several of them with different widths or some way to adjust the width. The Crabb type works for all (common) pitches.

 

A hard plastic version would probably work ok. It should 2mm or less thick so you can file the reed while it's in the holder. 

Edited November 16, 2018 by alex_holden

[Sprunghub]

HI Alex - hopefully you will see this.....I have some 7mm thick acrylic from another job.  I reckon I might be able to replicate that metal jig of yours......it's not a very big section left, but I reckon I can get 7.5 x 7.5 cm out of it which I think will be big enough.    

 

I also have plenty of spare 2mm and 3mm, so could create a twin layer option if the routing of the acrylic is too difficult.  I "get" the process of pushing the reed forwards in to the jig sound it.

 

One thing - if you could - would it be possible to have a picture of the holder without a reed in it ? so I can see the air hole slot  ?  

Edited November 17, 2018 by Sprunghub

[alex_holden]

6 hours ago, Sprunghub said:

HI Alex - hopefully you will see this.....I have some 7mm thick acrylic from another job.  I reckon I might be able to replicate that metal jig of yours......it's not a very big section left, but I reckon I can get 7.5 x 7.5 cm out of it which I think will be big enough.    

 

I also have plenty of spare 2mm and 3mm, so could create a twin layer option if the routing of the acrylic is too difficult.  I "get" the process of pushing the reed forwards in to the jig sound it.

 

One thing - if you could - would it be possible to have a picture of the holder without a reed in it ? so I can see the air hole slot  ?  

 

The vent slot is 4x17mm. If you make it in two parts it's easier to undercut the edge.

[Sprunghub]

Very many thanks for that Alex.....I have the table and bellows all ready to make the reed jig after a good day today, including drawing up the 440hz record of the existing tuning via that App you recommended. 

 

Seeing your 'plate' I think a 2-piece option will be the way for me to go for ease of making and function. 

[Sprunghub]

On 11/12/2018 at 4:43 PM, Geoff Wooff said:

measure the pitch  of each reed   whilst  they are all still in the instrument... make a chart  of some sorts  to note  each  reed's exact pitch.  Then when each  reed  is on your tuning jig  measure the pitch  again  and tune  the  reed  up or down  by the difference  between the two measurements..

 

Say a reed  is  8  cents  sharp of  your required pitch  when played  IN the instrument  and on the tuning jig  it shows  13 cents sharp  then you need to  flaten the reed  until  your  tuner  reading is  +5 cents. 

 

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Further to the above advice - which uses small numbers and feels 'safe' ?I am now in the real world and working on the table.  I am just checking now because I am working with 'big' numbers compared to Geoff's example and whilst I suspect the same calculus applies, anything to do with numbers / maths is my Achilles Heel in life so I want to double check before potentially 'messing up'.  I am guessing the 'big' differences may apply because I am working with one of the biggest reeds ?

 

As an aside, because I took the x3 'E's out to test the tuning desk, I did fettle the high/small E last night and at about '7 cents difference ( from 40 to 47 ) , between concertina and table at 'about' 7 c sharp on the table it went back into the instrument and was bang on.    My concern is that the large E reed, having shown as E+45 cents sharp in the Tina is Fb-23 on the table.  I think that I have deduced that past +49/50 cents sharp it becomes -50/49 flat in the next note up ?? so I have a differential of  +/-28 cents ?  My initial tip soldering took it to D 'something' and I am back up to 'E' after a fair bit of lead filing, so just checking that I need to be at a number as 'high' as 23 cents sharp on the table to be down at a playable E in the instrument ?  Sorry if all this seems obvious to those who have the confidence to know but this is making me sweat despite the weather turning! 

 

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[alex_holden]

That does sound odd. It's showing as 100-23=77 cents sharp on the table, 45 cents sharp in the box, so you're aiming for 77-45=32 cents sharp on the table to get 0 in the box. That looks like too large of a difference to me. Usually it's more in the range of +5 to +12.

 

Of course if you're only adding solder to the tip and taking it away again, you can afford to experiment a bit without doing permanent damage to the reed.

[Chris Ghent]

The numbers seem large, could the instrument be in a different pitch?  Also, the state and nature of the valves will affect the offset size. Any offset that large and I would change the valve first.

Edited November 19, 2018 by Chris Ghent

[Sprunghub]

Thanks for that Alex,  it has been a little bit trial and error, but I ended up with the reed at about '0' and 'green' on the App on the table, I put it back in the Tina to check what was happening and it was now at around  E 3  - 25 cents (flat)  from the original 45 sharp, in the box. 

That restored the base line for Geoff's calculus in my number befuddled head and made the numbers smaller and easier to deal with to tweak it back up on the table to mid 20's sharp.  Once in the box again it is showing green at +/- 1 or 2 cents through the pull at 440hz.   Hopefully I will get a 'knack' for it as I go, or I may be older than the instrument by the time I get to the last one!  I didn't need to fettle too much metal on the reed, but most of the lead has gone! 

 

Yes Chris, it is in 452 tuning currently.  Valves and pads have all been done and she plays well within her own tuning......just not the right tuning?    

[Theo]

Also worth bearing in mind that several other factors can affect the pitch.  So it's worth taking some time to make everything that can affect the pitch is just right.

How hard you sound the reed, generally the pitch will drop as you play harder/louder but this is more pronounced on some reeds than others. 

Reed tongue being slightly off centre can make the pitch less stable

Bits of solder hanging over the edge of the reed tip can do strange things.

Bits of foreign matter can get stuck in the gap down near the clamped end of the reed and can make the pitch go up

Reed shoe not quite tight enough in the reed pan can make the pitch sound flat

 

 

[d.elliott]

Also be aware that the 'sound in the box' values may be the same between the reeds on the chamber side, and the flat side of the reed pan, but take both out together and the sounds on the tuning rig will be different. You cannot tune both reeds from the same button to the same value on the rig, put them back and sound them again and expect the same accuracy push to pull. So don't risk mixing them up either. You need to treat each reed as a separate entity. not as part of a pair.