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Conn 7M G#/C# linkage explored...what fettling to do?

DavidUK

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This thread follows on from this one: Saxophones - Conn 7M - G#/C# linkage "discovered"

I pulled the 7M out at last to have a look more closely at the removable linkage described in my previous thread, the one which supposedly makes C# feel a little mushy.

Removing this linkage, which I did for the first time today, makes little difference as it's the C# key alone which is the issue and not the extra burden of the G# key. I replaced it.

This short video shows the set up from touch piece to key cup...

View: https://youtu.be/ctxy5rjf9W8


I've observed the following:

1/ The C# actuating rod end in the fork near the C# key cup is very close to the fulcrum with little leverage on it. If it had been at the open end of the fork there would be far more leverage and control.

2/ Applying light pressure to the C# touch piece in the pinky table there is a tiny bit of movement in the rod end before the key cup starts moving.

3/ Once the key cup is fully open there is no mechanical "stop" to the key so my tendency is to keep pressing the C# touch piece until the attached G# foot (felted under) meets the body tube and I can press no more. This extra travel to the C# touch piece at the pinky table is 4mm. That's 4mm of extra stubborn movement which my finger tells me it should be pressing until it comes to a stop, whereas the key cup was fully open 4mm ago. As I continue to press after the key cup is open the long connecting rod deflects perhaps 1mm to take up the strain and then returns to normal once pressure is removed. This extra pressing of my finger against the springiness of the long brass rod is what I believe is causing 95% of the "mushy" feeling. And of course it's totally unnecessary to press it this far. It explains precisely the feeling through the touch piece.

4/ The fork and pin linkage is dirty with contaminenents and needs cleaning.

What's my best solution to these? Is there any other issue you can see?

I think...

1/ I can't change the mechanics.

2/ Remove the fork and insert a closer fitting cork surrounding the rod end. Too close fitting and it will bind. I think it's probably just right at present.

3/ I can't see where or how I could place a "stop" to the C# rod. But a mechanical stop would solve the problem as it would limit my ability to press past the maximum key cup opening. How could this be done? Or should I just learn that I don't have to press so hard to fully open the C# key? This may be the ultimate solution.

4/ Clean and re-lubricate. I usually use gear oil as @Stephen Howard recommends but is that best on a corked rod/fork arrangement?

Any other observations and suggestions please?

More photos under...



 
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DavidUK

DavidUK

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I found something else... when pressing the C# which in turn pulls down the G# touch piece and actuates the G# key, there's a distinct two stage feel. You press C#, it gets half way down then there's a little resistance before it goes the rest of the way.

Here's the culprit...



In the centre of the photo you can see the G# lifter arm cork has a depression in it. A little trough which the pin drops into but then more pressure is needed to get it out again, hence the stepped feel. This isn't noticeable when pressing the G# touch piece itself, only when the connected C# is pressed.

So I'll replace this cork. I'm thinking a strip of PTFE would be better as it won't get deformed and is better at sliding things across it. Getting the correct thickness may be an issue - haven't worked with PTFE before. Any other suggestions for material welcome.
 
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DavidUK

DavidUK

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I've ordered some PTFE tubing (£2.30 for 0.5m ebay) to fit over the G# pin to slide against something stuck onto the arm it moves along.

It's 1mm thick over the pin so I'm thinking I'll remove the "dented" cork and replace with either thin felt or etched one side teflon (PTFE) sheet (as sold by Dawkes) having firstly ensured the surface under is flat.

Although PTFE it supposedly tricky to stick I'd hope that contact adhesive would do the trick. Superglue as a last resort.
 

Colin the Bear

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The cork is worn and needs replacing. The advantage of using cork is that it can be filed/sanded to the perfect thickness in position. I can't imagine ptfe being simple to regulate.
 
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DavidUK

DavidUK

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I was thinking of a sized cork backing with a thin PTFE layer atop. That way I get PTFE on PTFE. The pin is always in contact with the G# arm so there's no bumping, no noise.

I'm not so sure the current lacquered brass pin sliding on cork, or PTFE sliding on cork, would be as good as PTFE to PTFE but there may be difficulties in application as you say.
 

Stephen Howard

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1,854
I've ordered some PTFE tubing (£2.30 for 0.5m ebay) to fit over the G# pin to slide against something stuck onto the arm it moves along.

It's 1mm thick over the pin so I'm thinking I'll remove the "dented" cork and replace with either thin felt or etched one side teflon (PTFE) sheet (as sold by Dawkes) having firstly ensured the surface under is flat.

Although PTFE it supposedly tricky to stick I'd hope that contact adhesive would do the trick. Superglue as a last resort.
Just stick some thin woven felt on it, and have done with it.

I've not found any glue that will reliably stick ptfe long-term to anything, other than epoxy adhesive.
 
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DavidUK

DavidUK

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I couldn't stand the wait so cut a piece of replacement cork for the G# lifter arm as you suggested Colin. Got it dead on first time.
Took the long C# rod out and cleaned it and where it locates. Put it all back together. A light oiling with EP80W-90 GL-4 gear oil and all was well apart from the over-travel on the C#.
Then I realised what should be stopping this, and wasn't... the felt buffer on the bell guard above the C# key cup was too far in. Removed it and introduced a round cork spacer behind it. Re-glued the buffer.
Dead on perfect again!
All seems well now. The C# travels just far enough with no rod bending. The G# rod slides along the lifter arm nice and smoothly.
Very satisfying piece of DIY tech. Just needed to use my eyes, and ears, the latter for a slight clunk before the buffer was extended, and for squeaky cork!
 

jbtsax

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I have had good results with teflon tubing by choosing a size with a slightly smaller diameter and "forcing" it onto the part so it is held in place with a "pressure fit". Some of my techniques include a bit of saliva in the tube to lubricate it, heating the part, and using a heated awl to expand the opening of the tube to get it started. The problem with stocking several different sizes is many vendors have a minimum length requirement making it very expensive.

When the closest size tubing is too large to fit snugly on the part, I hold a length of it over a small flame while gently pulling the ends to "stretch" and shrink it. The downside is that this leads to some waste.
 
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DavidUK

DavidUK

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Well, I have 0.5m of 4mm id 6mm od ptfe tubing on its way. Might fit the octave arm as that has a bit of electrical cable outer sheathing on it presently.
 
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