Reed Testing and development

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Reed Testing and development

Postby pipemakermike » Wed Aug 24, 2011 10:20 am

I have started this as a new topic as it has now strayed far from the original digital manometer thread.
I you are interested in the starting place for the work I am doing you can go here:-
http://www.machineconcepts.co.uk/smallp ... etting.htm
If you want to know why I am doing it you can go here:-
http://www.machineconcepts.co.uk/smallp ... lpipes.htm

Francis. I have thought of measuring the tip but my initial efforts have not shown that there is any correlation between tip measured thickness and reed performance. I suspect that the most importent measurement of the tip would be the opening and possibly the centre thickness at the tip of the blade.
I have been looking at a non-contact way of measuring the tip and a way to avoid the thickness at the sides of the tip dominating the measurement.
My first efforts look as though they might show a method. I have now got the USB microscope working and I can get a good closeup of the tip. When I get a bit of time I plan to make it possible to have a wire of known thickness in the picture so that comparative measurements can be done then I will have reliable numbers to relate to reed performance. First pictures are below:-
[p]
Attachments
ross sample reed edge.jpg
ross sample reed edge.jpg (41.96 KiB) Viewed 1416 times
reed with poor tip shape.jpg
reed with poor tip shape.jpg (34.05 KiB) Viewed 1416 times
reed with good tip shape.jpg
reed with good tip shape.jpg (38.16 KiB) Viewed 1417 times
pipemakermike
 
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Re: Reed Testing and development

Postby Francis Wood » Thu Aug 25, 2011 12:28 pm

Mike,

Local results may suggest otherwise but the thickness of the reed tip at various areas along this edge will decide the effective mass of the cane and, inescapably (?), its vibration behaviour.

Excellent that you have found a use for the USB microscope, an ideal tool in these investigations.

Another (less convenient) method of measuring the aperture is to project light from a small LED source through the staple, directing a beam of light through the tip, and casting an illuminated shape which can be measured with a ruler. Calibration would be provided by the shadow of a wire of known thickness as you already do, preserving all distances as a known quantity. I have observed this effect and noted it as potentially useful, though I have not done similar investigation.

All highly useful research and I'm keen to follow its progress!

Francis
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Re: Reed Testing and development

Postby Richard Evans » Fri Aug 26, 2011 7:52 pm

I have built a pressure testing system using a bottled gas demand valve. For those who don't know, this releases compressed air at a user-defined pressure, in a volume which autmatically matches usage. The air supply is the same compressor I use for the gun drills. If you hook it up to a set of pipes, the sensation is very odd since your left arm has no effect on the pressure supplied to the reeds. Squeezing harder simply reduces the bag volume, but the constant pressure is maintained. Your right arm tends to flap a bit too.
I originally thought I would be able to test a chanter without using the bag- just a stock attached to the air line. I quickly discovered that in those circumstances the chanter would always be out of tune, which I should have realised would be the case. The bag of course has a very marked effect on tuning, particularly the neck region. Presumably the chanter stock internal volume is also important- I haven't tested this but these days all our sets have split stock and I put a thin foam plastic filter in the top of the stock as a matter of course.

It is actually several years since I used the system- I now find the digital manometer more convenient- but it is still there if I want it.

Cheers
Richard
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Re: Reed Testing and development

Postby Barry Say » Sun Aug 28, 2011 7:49 pm

I have taken a little while to catch up with this thread and there are several aspects on which I would like to comment and the first is tip thickness. Colin Ross made a concerted effort to put reed-making on a predictable footing, measuring his work as far as possible in an attempt to make his skills available to others. This was only partially successful, partly because chanters have varied so much over the years and partly because of the reluctance of pipemakers and reedmakers to give up the methods they themselves have become accustomed to. However, one particular measurement that seems to be consistent is a combined tip thickness of 0.015 " for F reeds. This is most easily measured with a pair of dial calipers placed across the tip of the reed. The thickness of the tip predominately affects the top notes particularly the high b. A thin tip makes a flat note and a thick tip can make the b sharp.

I have looked closely at the picture of the Ross reed and I do not think that Colin would wish this to be presented as an ideal reed as it falls far short of the standards he himself sets. There is, of course no guarantee that this reed has not been 'adjusted' since it left Colin's hands. I would make 4 points
  1. The upper blade looks considerably thicker than the lower. Colin pays great attention to having the blades of equal thickness.
  2. The upper blade is thinner at the right and the lower at the left. This is generally due to a bias in rubbing down. This is a problem which Colin is very aware of and takes steps to avoid.
  3. The aperture is irregular, as opposed to the ideal shape indicated in the third photograph.
  4. Observing the way the blades go out of focus, it looks as though the lips of the reed are bending inwards near the tip. This could be a symptom of reed ageing.

Having a made these points I would also like to suggest that there is no reason why any of these faults should adversely affect the reed's performance. Many unattractive reeds give excellent results.

So, I would urge caution before readers draw conclusions based on this particular photograph. I think this also illustrates the possible difficulties associated with describing or presenting the work of others in forums such as this without first seeking their approval.

More later.

Barry
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