alfredo_buscatti
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My involvement (Mike Smith, MS) with GL Pease’s (GLP) concept of“the articulate pipe” began when I heard Neill Archer Roan’s use it in podcast on Olie Sylvester’s site. Roan used the phrase “the articulate pipe” and referenced GLP as its originator. Roan said that American pipe artisan Will Purdy’s pipes totally embodied this concept and even went so far as to say that he didn’t understand why his pipes didn’t sell for thousands of dollars as they delivered the taste of blends in a superlative way.
I’ve not communicated with Mr. Purdy or Mr. Roan but have traded a number of emails with GLP and pipe maker Mike Brisset (MB) in the effort to try to understand why Purdy’s stems are unique. What follows is a pastiche of their responses to my questions.
(GLP) One thing to remember is this: there are infinite many ways to create an exit passage with a constant cross-sectional area. Mike (MB) is right - defining the radial cross-section mathematically is trivial. You can imagine a straight drilled hole. If you flatten one end of the tube, the instantaneous radial area will remain constant at any given point, but the flow characteristics will change. That's more or less what we're talking about - how is that tube flattened. What's the shape of the curve that represents the AXIAL cross-section.
(MS) The axial cross-section refers to the inside of a stem that is in the shape of <, where the smallest point is closest to the round part of the stem that exits the tenon and the largest part is at the button. Of course that round hole must flatten to become a surface to enter the smoker’s mouth.
(GLP) What we are after is the shape of the curve, the axial cross-section, that describes the internals of the stem, and most especially that curve at the button.
To complicate matters, you can almost always improve the mouthpiece, but it takes care. If you go too far in any direction, the structure of the bite region can be compromised, and you'll end up with something too fragile to be useful.
Also, I'm actually not convinced that a constant flow is ideal. I'm not convinced that some slight restriction in the middle, coupled with some expansion at the bit end isn't preferable. I do know that the way Will cuts his mouthpieces, and other makers, I'm sure, results in a smoking experience that is sufficiently different - TO ME - to stand out a bit. When I refer to it as articulate, that's precisely what I mean. (MS), italics mine.
It IS a minor thing, but if one is smoking with their critical faculties engaged, it can be important.
(The downside of it is that if I smoke one of my prototypes in a Purdy, and it's not quite right, the flaws in the blend seem to be amplified! Maybe it's not such a downside, as it does provide an interesting "litmus test)."
It's important to realize that my hand waving about flattening a tube assumes that it's desirable to maintain that constant cross sectional area. I'm not sure that's the case. Most mouthpieces do have some reduction, some taper along their length, and this doesn't seem to be a bad thing.
it's a tin of worms. There are a lot of opinions "out there," and I suspect very few of them can be backed up with empirical evidence, or, *gasp*, actual fact.
As an addition, speaking of a well-known piper’s specifications for shank/stem bore diameter, he advocates 4.7mm throughout, or as much as the pipemaker can accommodate him where the stem is flattened, I suppose. Here GLP said to remember that the cross-sectional area increases with the square of the increase in the diameter. The increase from 4mm to 4.7mm reflects a 1.38x increase in area and accordingly increases the temperature of the smoke at the exit.
This is the end of GLP’s comments; on to MB.
The following are three questions that I asked MB:
1. Looking as deeply as I can into the stems of the pipes you made for me you very definitely are doing this or something very much like it. Just what configuration do you use? If this is not the < then what is its shape and why do you use it?
2. You said that it would be easy to plot a mathematically ideal airway/exit. . .but that in practice it would be impossible to apply this shape to the interior of the stem. Why?
3, Why do you say that pipe makers would have discovered the ideal shape for the stem's airway/exit long ago, and that thus the < shape is just another variation?
I will reproduce MB’s answers to these questions in the order that they were received; I didn’t rearrange any of his text.
I don't believe that smoke exit hole geometry is something that most pipe makers obsess over, at least not to the extent that some pipe smokers do. If there were an ideal size and shape, those crafting a stem by hand would have discovered it long ago. Hence the large variation of exit hole shapes among different pipe makers.
Geometry itself will not magically transform a harsh or wet or hot smoking pipe into a pleasant smoker, or a good smoking pipe into a better one.
It would be easy to plot a mathematically ideal airway/exit hole design where the cross sectional area would remain constant. This would insure a constant velocity and pressure through out the stem, possibly resulting in slightly less condensation in the smoke passage. In practice, it would be nearly impossible to physically apply this shape to the interior of the stem.
What do we want or not want from a stems airway/exit design?
We don't want it to produce condensation.
We want a smooth, easy draw.
We want a quiet draw.
We would like to reduce the temperature on the tongue.
I will try explain this in reverse order.
The purpose of the slit at the exit hole is to produce a wider stream of smoke exiting the stem. The effect is two fold, the temperature of the smoke is distributed over a larger area of the tongue, rather than one small spot, and therefore feels cooler. The same distribution applies to the tobacco, and results in a greater flavor sensation.
The shape of an ideal airway/exit would be nearly impossible to cut by hand because of the precision required and the inability to control the cutting instrument in a confined area.
Third on the list of what we want is a quiet draw. If a pipe whistles or hisses, we usually attribute it to the entrance hole at the tip of the tenon, and most pipe makers cut a bevel or otherwise round over the sharp edges of the hole. This goes a long way in reducing or eliminating the noise. What is often overlooked is the smoke passage through the rest of the stem. Any sharp edge, abrupt angular change or restriction at the exit hole can set up a series of pressure changes that induce vibration and hence noise.
Next, a smooth easy draw. The way to achieve this is obvious.... a larger airway. But this larger diameter will have to be flattened into an oval shape to keep the stem from becoming too thick at the lip end. The transition will have to be done as gradually and smoothly as possible, keeping in mind the requirements of the other 3 parameters.
Finally the necessity to eliminate condensation caused by the airway design itself.. If the other 3 requirements have been properly addressed, they will go a long way in eliminating moisture and the final step is relatively easy to accomplish. The entire internal surface of the stem must be polished. "Drag reduction"
Getting back to your original question of why do I use a < shape exit, I use it because it provides a manageable method to enhance all 4 qualities that I expect from a pipe stem. (Italics MS)
This shape allows for smooth transitions, eliminates sharp edges, fans out the smoke flow and permits incorporating a thinner bit.
Having said all of the above, I do not believe that the exit design alone is going to make or break a stems performance.
What I do know is that pipe smokers as a group will seldom agree on anything regarding the hobby. We are overwhelming individualistic and once convinced by our own experiences, virtually nothing will change our likes and dislikes.
What I do find disturbing is that many inexperienced and some not so inexperienced pipe smokers are convinced by the "experts" opinions as to what is good and bad.
What is worse is that much of this anecdotal information is exchanged over the internet as infallible fact.
I’ve not communicated with Mr. Purdy or Mr. Roan but have traded a number of emails with GLP and pipe maker Mike Brisset (MB) in the effort to try to understand why Purdy’s stems are unique. What follows is a pastiche of their responses to my questions.
(GLP) One thing to remember is this: there are infinite many ways to create an exit passage with a constant cross-sectional area. Mike (MB) is right - defining the radial cross-section mathematically is trivial. You can imagine a straight drilled hole. If you flatten one end of the tube, the instantaneous radial area will remain constant at any given point, but the flow characteristics will change. That's more or less what we're talking about - how is that tube flattened. What's the shape of the curve that represents the AXIAL cross-section.
(MS) The axial cross-section refers to the inside of a stem that is in the shape of <, where the smallest point is closest to the round part of the stem that exits the tenon and the largest part is at the button. Of course that round hole must flatten to become a surface to enter the smoker’s mouth.
(GLP) What we are after is the shape of the curve, the axial cross-section, that describes the internals of the stem, and most especially that curve at the button.
To complicate matters, you can almost always improve the mouthpiece, but it takes care. If you go too far in any direction, the structure of the bite region can be compromised, and you'll end up with something too fragile to be useful.
Also, I'm actually not convinced that a constant flow is ideal. I'm not convinced that some slight restriction in the middle, coupled with some expansion at the bit end isn't preferable. I do know that the way Will cuts his mouthpieces, and other makers, I'm sure, results in a smoking experience that is sufficiently different - TO ME - to stand out a bit. When I refer to it as articulate, that's precisely what I mean. (MS), italics mine.
It IS a minor thing, but if one is smoking with their critical faculties engaged, it can be important.
(The downside of it is that if I smoke one of my prototypes in a Purdy, and it's not quite right, the flaws in the blend seem to be amplified! Maybe it's not such a downside, as it does provide an interesting "litmus test)."
It's important to realize that my hand waving about flattening a tube assumes that it's desirable to maintain that constant cross sectional area. I'm not sure that's the case. Most mouthpieces do have some reduction, some taper along their length, and this doesn't seem to be a bad thing.
it's a tin of worms. There are a lot of opinions "out there," and I suspect very few of them can be backed up with empirical evidence, or, *gasp*, actual fact.
As an addition, speaking of a well-known piper’s specifications for shank/stem bore diameter, he advocates 4.7mm throughout, or as much as the pipemaker can accommodate him where the stem is flattened, I suppose. Here GLP said to remember that the cross-sectional area increases with the square of the increase in the diameter. The increase from 4mm to 4.7mm reflects a 1.38x increase in area and accordingly increases the temperature of the smoke at the exit.
This is the end of GLP’s comments; on to MB.
The following are three questions that I asked MB:
1. Looking as deeply as I can into the stems of the pipes you made for me you very definitely are doing this or something very much like it. Just what configuration do you use? If this is not the < then what is its shape and why do you use it?
2. You said that it would be easy to plot a mathematically ideal airway/exit. . .but that in practice it would be impossible to apply this shape to the interior of the stem. Why?
3, Why do you say that pipe makers would have discovered the ideal shape for the stem's airway/exit long ago, and that thus the < shape is just another variation?
I will reproduce MB’s answers to these questions in the order that they were received; I didn’t rearrange any of his text.
I don't believe that smoke exit hole geometry is something that most pipe makers obsess over, at least not to the extent that some pipe smokers do. If there were an ideal size and shape, those crafting a stem by hand would have discovered it long ago. Hence the large variation of exit hole shapes among different pipe makers.
Geometry itself will not magically transform a harsh or wet or hot smoking pipe into a pleasant smoker, or a good smoking pipe into a better one.
It would be easy to plot a mathematically ideal airway/exit hole design where the cross sectional area would remain constant. This would insure a constant velocity and pressure through out the stem, possibly resulting in slightly less condensation in the smoke passage. In practice, it would be nearly impossible to physically apply this shape to the interior of the stem.
What do we want or not want from a stems airway/exit design?
We don't want it to produce condensation.
We want a smooth, easy draw.
We want a quiet draw.
We would like to reduce the temperature on the tongue.
I will try explain this in reverse order.
The purpose of the slit at the exit hole is to produce a wider stream of smoke exiting the stem. The effect is two fold, the temperature of the smoke is distributed over a larger area of the tongue, rather than one small spot, and therefore feels cooler. The same distribution applies to the tobacco, and results in a greater flavor sensation.
The shape of an ideal airway/exit would be nearly impossible to cut by hand because of the precision required and the inability to control the cutting instrument in a confined area.
Third on the list of what we want is a quiet draw. If a pipe whistles or hisses, we usually attribute it to the entrance hole at the tip of the tenon, and most pipe makers cut a bevel or otherwise round over the sharp edges of the hole. This goes a long way in reducing or eliminating the noise. What is often overlooked is the smoke passage through the rest of the stem. Any sharp edge, abrupt angular change or restriction at the exit hole can set up a series of pressure changes that induce vibration and hence noise.
Next, a smooth easy draw. The way to achieve this is obvious.... a larger airway. But this larger diameter will have to be flattened into an oval shape to keep the stem from becoming too thick at the lip end. The transition will have to be done as gradually and smoothly as possible, keeping in mind the requirements of the other 3 parameters.
Finally the necessity to eliminate condensation caused by the airway design itself.. If the other 3 requirements have been properly addressed, they will go a long way in eliminating moisture and the final step is relatively easy to accomplish. The entire internal surface of the stem must be polished. "Drag reduction"
Getting back to your original question of why do I use a < shape exit, I use it because it provides a manageable method to enhance all 4 qualities that I expect from a pipe stem. (Italics MS)
This shape allows for smooth transitions, eliminates sharp edges, fans out the smoke flow and permits incorporating a thinner bit.
Having said all of the above, I do not believe that the exit design alone is going to make or break a stems performance.
What I do know is that pipe smokers as a group will seldom agree on anything regarding the hobby. We are overwhelming individualistic and once convinced by our own experiences, virtually nothing will change our likes and dislikes.
What I do find disturbing is that many inexperienced and some not so inexperienced pipe smokers are convinced by the "experts" opinions as to what is good and bad.
What is worse is that much of this anecdotal information is exchanged over the internet as infallible fact.
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