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Octave key issues.... interesting discovery

Tenor Viol

Full of frets in North Shropshire
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As you may recollect, I was having some issues with my octave key on the tenor - the neck key has a habit of lifting very slightly when octave key is pressed and G and below are fingered. This causes a slight leak and D in particular sounds terrible with a lot of harmonic.

Interesting discovery: I was at a friend's dinner party last night - we were all musicians. A very good pro flautist and teacher was there. His father was an engineer and he grew up with a lot of tools such as metal working lathes etc at home. Consequently, he's a very proficient tech.

We played all sort of music (I mostly played cello - Haydn trios etc). The tenor sax came out and I explained the issue. After a few minutes close examination, he thinks he knows what the issue is. I will try to post a photo later to demonstrate, but when you depress the octave key, part of the mechanism lowers and it is held up by a cork pad. The cork pad compresses, which causes the neck key to lift slightly. The problem is therefore the compressible nature of the cork - it needs to be replaced by something solid. This explains why having had it fixed 2 months' ago, it is still a problem.

As an interim measure, he placed two small pieces of adhesive label on the sax body, which in effect compensates for the cork compression.

Seems to work :mrcool
 

kevgermany

ex Landrover Nut
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Interesting to know. Perhaps you're also pressing a little hard....

Wouldn't be a big job to replace the cork with a piece of wood with a layer of cork to absorb the noise and shock. Wonder what the repairers will make of this.
 

Colin the Bear

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Burnley bb9 9dn
I use all sorts of bits and pieces. You can get sticky back felt squares and silicone etc. from the pound shop. They're for the bottom of ornaments to stop scratching and slipping and such like, but with a little scissor snipping work a treat as rattle stoppers on the Bari.

The usual reason for the neck pad lifting is either regulation or lubrication.
 

jbtsax

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Beautiful Springville, Utah USA
This is a common issue when traditional cork is used on a key that is pressed with a degree of pressure. It's nature to contract and then relax makes it ideal for neck and tenor corks, but not so much for keys that require regulation (one key operates another).

Many techs have gone to Tech Cork for applications require a material that does not easily contract. Depending upon the thickness required, I will often use a layer of tech cork with a .5 mm layer of Synthetic Felt to add to the quieting of the key.

In any event, one should allow approximately 1/16" inch gap between the floating octave lever post and the neck ring to insure that the neck octave doesn't accidentally open when high G is played.
 

Stephen Howard

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Such problems can sometimes be indicative of damage or build quality issues with the mech.
All modern octave key mechs have a degree of latitude built in when it comes to the 'throw' (the distance the mech moves) and the height the octave key pads will open - and if the amount of travel added by the compression of a piece of corks makes a difference, it usually means that the throw is too large.
A well built, properly set up swivel mech (as found on Selmers and most modern horns - readily identifiable by the 'see-saw' bar in the middle) should work with no corks/felt at all up to a point, and should at least work with far more throw than you'd ever want to use.

octave_throw.jpg
Imagine a pizza, cut up into four quarters. The circumference of one quarter of the pizza represents the entire throw of the octave key with no corks or felts fitted - and it probably won't work properly. If you cut that quarter in half again, the circumference you're left with represents the functional throw of the mech (i.e. it will work). If you then cut that piece in half again this will represent the working throw of the mech, which is to say that this amount of throw that will be comfortable to use and will be fast and efficient.

So you can see that there's a bit of leeway between the working throw and the functional throw, and the various corks and felts are used to keep the mech well within the functional throw. On a well set up mech you might have to press the thumb key down about 5mm - a poorly-set mech maybe 8mm... and a real old clunker maybe a centimetre. But in each case the mech will still work because the throw is still within the 'functional slice of the pizza'.
Now - if the amount a piece of cork compresses is enough to tip the mech out of the functional slice, then it's already way beyond the working slice...which means that something is wrong.

What could be wrong - apart from the mech having way too much throw already?
It's usually one of two things - either the mech has been damaged (typically bent) or it's not that well built...and in the latter case this usually means that something is binding, or it's all too loose and most of the throw is wasted in taking up the excess play in the mech.
To test for this, put your finger over the pin that rises above the crook tenon socket to hold it down, leave the G key open and then press the octave key. Note how far the thumb key moves before you feel a definite resistance (the the body key cup starts to rise against the downward force of the G key foot). It should be about a millimetre.

Testing for a bent mech is easy enough, just get a small screwdriver and give the octave key mech rod screw (not the thumb key screw) a half turn back and forth and watch the mech as you do so. If you see it rise and fall as you turn the screw then you've got a bent mech - or at least a bent screw. If any of the keys turn with the screw it usually means that key is bent...or it could just mean you need to oil the mech.

One gotcha to watch out for is that the G key foot (which sits atop the body octave key cup) rises sufficiently. It's this key that really sets the maximum throw of the octave key mech. If pressing the octave key down raises the body pad higher than the foot of the closed G key will allow, the mech will act as though the G key is open...which means the crook octave pad comes into play.

Putting firmer buffers on the mech will cure the symptom, but it won't solve any underlying problems.
No big deal, of course - if it works, it works - but it's worth bearing in mind that it could work better.

Cheers,

Steve
 

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