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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 5:35 am 
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Ah, well, my feeling is we can safely put this whole question to rest, at least for the time being. So far we have absolutely no evidence for "chambering" in front of us. We have a vague statement by a single 19th century writer (Rockstro) who is known to be an unreliable source. And nothing more!

As I said above, to warrant resurrecting this topic, we'd need a graph of a carefully measured bore and some datum lines added to stake out the claim. And of course to give us scope and permission to take pot-shots at. At this stage, I'm happy to write off any allegations of chambering as evidence of bore compression. We know that's a thing, we don't know that "chambering" is. Quod non erat demonstrandum.

And Conical Bore, I actually have here some X-rays of a 19th century Metzler flute taken many years ago by Sydney radiologist Ian MacKenzie who has gone on to become a flute and pipes maker. They were surprisingly disappointing, but for really obvious reasons when one thinks about it.

Firstly, x-rays work well with bones vs soft tissue. Wood, even as dense as cocus isn't as opaque as bones. And the bore is shadowed by the wood at front and back, and its sides blurred by the curvature of the inner surface. So it's very hard to make out the demarcation between wood and bore.

Secondly, it's 1:1 y:x ratio. When you look at the bore images above, we show them at about 40:1 to highlight fine detail. So what you see as bold vertical leaps are probably less than 1mm. When you see them at 1:1, you see nothing. Air molecules though are very small. They see lots!

I do remember someone in Boston (from memory) doing CT or MRI scans, which were much clearer, but again, I think, still 1:1 ratio. I imagine there are variant industrial technologies that offer rescaling. Or that offer sufficient resolution to permit rescaling.

We do have to be careful in interpreting drawings. For example, the two graphs of multiple bores made by me were not made with the intent of looking for "chambering" or even bore compression, and so cannot be safely regarded as indicative of either. They were broad bore trend examples. There might be only one or two measurements made in the areas where such anomalies would surface.

The Potter bore measurement however was made with detecting bore compression in mind. I made lots of measurements in the afflicted areas to get really good data. Eight each in the areas of the three tenons alone, 66 all up. Anyone seeking to assert evidence of chambering would need to take lots of measurements. The crazier your assertion, the better the proof needs to be.


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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 8:49 am 
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Terry McGee wrote:
Ah, well, my feeling is we can safely put this whole question to rest, at least for the time being. So far we have absolutely no evidence for "chambering" in front of us. We have a vague statement by a single 19th century writer (Rockstro) who is known to be an unreliable source. And nothing more!


With respect, this statement seems dismissive of some very cogent arguments put forth by paddler. We are not limited to a vague statement from a single source, and while it is interesting that Rockstro made the observation (and I agree that it is not in itself "evidence") it does make one take a closer look to see what he is talking about. In this case, paddler made some very telling observations based upon data that you yourself provided, so there is definitely some strong evidence before us! It is true that bore measuring has limits on how refined it can be, depending upon tools and technique, but I've measured a fair few bores myself and one can achieve a pretty good picture of bore variations if one is willing to take enough data points. The question is, what was your method with these bores? Was it consistent from flute to flute? You don't seem like one to do sloppy measuring :-) So based upon that I'm guessing that regardless of how broad you were being, you probably took pretty accurate data points from these bores? Because paddler spotted what to my eye are some very interesting (and repeating) trends among those R&R flutes that are not exhibited on other bore profiles. Even granting that your measuring method was very "broad", isn't it noteworthy that these R&R flutes exhibited these repeating variations and other bores did not?

Looking at paddler's numbered list of points showing what is unique about the R&R bores compared to others is also worthy of evaluation. Those are some pretty noticeable peaks on those R&R bores (relative to a projected datum line), and while the compressed nature of the graph exaggerates their height I don't think that means that they can therefore be dismissed, simply because they show up on all of the R&R flutes except at the head tenon, which is also interesting. How would you account for these inconsistencies?

Terry McGee wrote:
So what you see as bold vertical leaps are probably less than 1mm


A bulge in a bore that is anywhere near 1mm is a lot! Spread that bulge along 25 or 30mm of bore length and that is a significant perturbation. It may not look like much when you peek inside the bore, but it is certainly enough to impact the behavior of the flute, wouldn't you agree?

Anyway, we can all agree to disagree of course, but I think paddler put forth more than enough evidence of chambering that it would certainly be worthy of a much closer examination.

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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 1:12 pm 
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Terry, you seem to be saying that your graphs are not worth looking at, since you can't trust that the
largest and most obvious features shown on them actually exist or correspond to real data. Did you just
make up those peaks that you plot for all the Rudall flutes? They appear on all of the different graphs
you have posted that include Rudalls, and on no other kind of flute. They surely can not have occurred
randomly. And what about the data that Casey posted on Rudall bore profiles. That shows the same basic
pattern too. What is your reasoning for ignoring that data?

When you are going to publish data, in the form of graphs or in any other form, you really should be sure to
collect your data objectively and then draw your conclusions from the data, not selectively use data to back
up conclusions you have already decided on, and then ignore the same data if that contradicts your conclusions.

Based on all available data so far, I still believe the evidence for chambering by back reaming at the last two
joints in Rudall and Rose flutes is strong, and I have yet to see any evidence that disproves this theory. Showing
a graph of a damaged Potter flute does not disprove the theory I have put forth about Rudall bores, no matter how
many data points you gather from it. You have also presented no evidence to disprove Rockstro's claim.


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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 1:39 pm 
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What's goal of chambering? Is it tuning, or timbre, or both? I'll admit I'm not getting the physics here, and also wondering why perturbations in the bore would not carry over into cylindrical flute making, like forming a silver flute over an armature with "bulges" strategically placed. Would chambering work on/with a boehm flute, or is it a technique specific to conical bore flutes?


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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 1:53 pm 
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PB+J wrote:
What's goal of chambering? Is it tuning, or timbre, or both? I'll admit I'm not getting the physics here, and also wondering why perturbations in the bore would not carry over into cylindrical flute making, like forming a silver flute over an armature with "bulges" strategically placed. Would chambering work on/with a boehm flute, or is it a technique specific to conical bore flutes?


It's not specific to conical bore flutes. I've talked with a headjoint maker (for Boehm flute) who confesses that he has made perturbations to the parabolic taper in the head of the flute to enhance certain harmonics, etc.. I have no idea if it worked with the Boehm flute. Rather, I should say that I don't have any information on whether it achieved what he claimed his objective was, since I'm sure tiny variations do have some effect. Just not sure how audible/measurable it is with the Boehm flute specifically. My own work with headjoints has led me to believe that the parabolic taper is more forgiving (or less, depending upon your viewpoint) about irregularities than is a conical bore.

As for cylindrical bore chambering, the most extreme and effective example I've ever seen was done by Yang Lan (who I mentioned previously) who did massive perturbations in the bore of a xiao (which is normally a completely cylindrical bore flute--the bei xiao anyway). I'm actually holding my own version of that flute right now. If you were able to bisect the bore and examine it you would see a sine wave effect, or as I like to put it: a bore that resembles a snake that has swallowed a series of rodents. He created this bore using some pretty sophisticated computer modeling and specialized measuring equipment, in a lab at the University of British Columbia. His results are impressive. I make traditional xiao as well and I'm very familiar with their strengths and weaknesses, and he engineered the weaknesses almost out of existence. Superior tuning balance and rich harmonic overtones. But as I've said before, my big critique is that it sounds less like a xiao as a result and more like a conical bore flute!

The point is that chambering is something that flute makers can and do utilize for strengthening notes or spot tuning. I have not done any of it myself (on purpose) though I've known it done by shakuhachi makers, I've heard of it being done by Baroque flute makers, and I've copied the xiao described. In the case of the xiao, it's impact on tuning was substantial.

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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 2:35 pm 
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PB+J wrote:
What's goal of chambering? Is it tuning, or timbre, or both? I'll admit I'm not getting the physics here, and also wondering why perturbations in the bore would not carry over into cylindrical flute making, like forming a silver flute over an armature with "bulges" strategically placed. Would chambering work on/with a boehm flute, or is it a technique specific to conical bore flutes?


I think it can be both. Perturbations in a bore may take the form of either constrictions or chambers, and they will have opposite effects.
The location along the bore of a chamber or a constriction will determine which frequencies are affected (either sharpened or flattened) by it.
The size of the chamber or constriction will determine the amount of sharpening or flattening. A perturbation in a specific location along
the bore might be targeted at a particular note to either sharpen or flatten it slightly, or to allow the tone hole position for that note to
be moved slightly, hence improving ergonomics. However, it is not easy to isolate the effect. You may affect some notes and not others,
and the notes affected may not all be affected in the same way (some sharpened and some flattened).

A perturbation may be placed such that it affects some harmonics of a note and not others, hence changing the voice. Or it might be placed
such that the nodes for certain higher octave notes move slightly and are better located with tone holes that are used as vents in cross-fingering
patterns for that note, hence making a previously difficult to sound, or poorly tuned, third octave note easier to play. The effects of perturbations
are larger on higher frequencies than on lower frequencies.

The size and position of the chambers discussed in this thread seems to indicate that they would have little impact on lower notes, which I think
is one of the sources of Terry's skepticism, but I wonder if they were intended to affect third octave performance or higher frequency harmonics.
It is relatively easy to lip low octave notes into tune, but the third octave notes are much more difficult, and were critically important in the music
these flutes were originally intended to play.

I honestly don't know the specific intended purpose of the perturbations I identified in the R&R flute bores, and I do not know if these specific
perturbations were the target of Rockstro's comments. I'm simply pointing out that they are there, they seem quite specific to R&R flutes, and they
are not inconsistent with Rockstro's statement. It is also well established, both in theory and in the practice of flute making, that bore perturbations
can be used to affect tuning and voicing.


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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 2:52 pm 
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In an attempt to shed a bit more data on this issue, here is a graph of bore profile data for R&R 3801.
I've had this data for a while and believe it came to me from JonC, but I'm not 100% sure of that.

I've added the actual measurements to the graph so you can see that data points themselves. The
curved line is computed to best fit the data points. The faint dotted line is a computed linear fit.
The high point for each of the peaks is the last data point taken on the flute section above it.
This means that the peak coincides with the tenon end. Note that this means that any tenon
compression that has taken place would cause the chamber to be smaller than it originally was.
Hence, any chambering that was originally present is likely to be under-represented in this
graph.

Image


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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 7:23 pm 
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Given that most C19 makers didn't use chambering, but RR did, then it is interesting to wonder what the chambering achieved, and why this approach appears unique to R+R. No one appears yet to have specified why it was done, but that many assume it was for a good reason.

If chambering is a positive feature, why didn't other flute makers use it? One possibility is that there are at least two ways to achieve the positive feature and that chambering was one of them, but not the only one., so other makers chose the other one. In this case chambering can be considered a hack rather than an advantage.

It is also possible that the R+R design had a defect, and that chambering was a way to overcome it, and the net result brought their flutes to the standard of other makers. In other words chambering was necessary, but it didn't provide a novel benefit.

Would it not be relatively simple to make two bodies, one with a chambered bore, and one without, and use the same player(s) and head joint and compare tuning, sonographs, and sounds and see if there is a difference, and if so, what?

Hugh

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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 8:09 pm 
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I think those are all good questions flutefry. I don't pretend to be able to answer them, but it is clear
that flute making involves many trade-offs in terms of bore profiles, tone-hole sizes and positions,
embouchure cuts etc, and there are often several distinct ways of addressing a single tuning issue.

At some level, all flute makers are producing more or less the same product, and doing it more or less
the same way. But yet there seems to be a little bit of magic about some maker's instruments compared
to others. It may be difficult to identify quantitatively, but nevertheless you see consistent preferences
among significant numbers of players. Trying to figure out where the important differences lie and why they
have the effect they do, in terms of issues such as timber, say, is difficult and leads makers to examine
instrument designs very closely. You can make a close replica of an old instrument, and end up copying
both its features and any damage it has sustained over the years. Or you can try to second guess the
original maker and remove details that you decide must be damage, but without really knowing. There is
a real danger of hubris in this endeavor.

If you replicate some of these old bore profiles precisely, and use other techniques to tweak the tuning
in order to get A=440 hz tuning, you still seem to end up with an instrument that retains some of the character
of the original, in terms of its voice. On the other hand, if you make a flute with a straight reamer you generally
seem to end up with an instrument that sounds boring. But those are just subjective comments, but if you
look at the pofiles of bores from the most prized modern makers, you see bore perturbations and some
surprising similarities (which unfortunately can't be posted in detail here due to board rules). I'm not saying
that the best flutes are chambered, but the bore profiles are certainly not straight.

The other issue is that if the intended effects in the R&R case were all to do with third octave notes, then we
would not tend to notice them on instruments that are refined to play optimally in the lower two octaves.
To do an accurate study you would have to make multiple accurate copies of an original fully keyed flute
(because the closed tone holes also create chambers in the bore which are acoustically significant) with and
with out back reaming the two lower joints. But even then you would have to decide how much tenon compression
had likely occurred in order to correct for that. Or you would make reamers that incorporated the tenon compression
and all the other bore characteristics. This is all quite a lot of work in order to try to answer a question that may not
yield any useful information.

It wouldn't really be a legitimate experiment to try to do this with simpler, keyless flute sections, because
the bore profiles would be different (due to lack of keyed tone holes), and so the locations of the various nodes along
the bore would be affected. You would also not be able to vent notes the same way as on the original flutes, so
the whole approach to fingering would be different. This is also a problem for computer modeling of the effects.

It is a puzzle, and I do understand Terry's skepticism, but I think it is clear that these bore characteristics do exist
repeatedly in R&R flutes. At one stage I even wondered if it was the result of wear due to some work-holding technique
they used to mount those flute sections in the lathe. Or perhaps there was some reaming done on either side of a joint,
after construction, to make sure that the transition from one flute section to the next did not produce an abrupt step
that might disturb air flow. And maybe that is what makes a subtle, but noticeably difference? Who knows?


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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 9:28 pm 
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paddler wrote:
In an attempt to shed a bit more data on this issue, here is a graph of bore profile data for R&R 3801.

Ah, very good, Paddler. That should give us something to sink our collective teeth into.

Now, would it be possible to give us the data in tabular form so any of us that wants a shot can use it to illustrate their own interpretations?

And the lengths of the three tenons? (or their XY co-ordinates)?

And can you also give us the fingerhole dimensions? I'd like to dig through my data for flutes of nearby serial number to see if we could be lucky enough to be able to compare like flutes. But we'd need to make sure they were the same model, and I'm guessing hole size and section lengths would be the best indicators. You might have other thoughts.

When you say "The high point for each of the peaks is the last data point taken on the flute section above it. This means that the peak coincides with the tenon end." Do we take that to imply that it doesn't also represent the first measurement in the next section? EG, if the LH section ends at 15mm diameter, the start of the bore at the bottom of the RH section socket isn't necessarily also 15mm. That the first data point in the RH section is 14.7mm, some small distance further down?


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 Post subject: Re: Rockstro
PostPosted: Sat Feb 15, 2020 9:43 pm 
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I don't have the actual flute in my possession, so I can't provide all the data you requested Terry, but here is the data I have,
which answers some of your questions. As I said, I believe this originally came from JonC some years ago. I graphed it to show
that it has the same overall shape as that of the other Rudall bores, which differ from the bore graphs of other flutes that you
have posted and the ones that I have measured. The point to focus on is not whether there is evidence of tenon compression,
which I believe there is, but to explain why these Rudall bore graphs have such a distinctive shape compared to those of other
flute bores, with respect to the flaring at the ends of the lower two tenons.

Here is a classic Rudall & Rose measurements for reference:
R&R 3801

000-18.3
010-17.9
020-17.6
030-17.2
040-17.2
050-17.2
060-17.1
070-16.9
080-16.7
090-16.6
100-16.3
110-16.2
120-16.1
130-16.0
140-15.9
150-15.6
160-15.3
170-15.1
180-14.9
190-14.8
200-14.7
205-14.7
208-15.0

Lower Section
000- Socket
020-14.7
030-14.4
040-14.1
050-13.9
060-13.7
070-13.4
080-13.3
090-13.1
100-13.0
110-12.6
120-12.5
135-12.7

Foot Section
000-Socket
020-12.4
030-12.1
040-11.8
050-11.7
060-11.6
070-11.4
080-11.2
090-11.0
100-10.8
110-10.4
120-10.4
130-10.3
142-10.5


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 Post subject: Re: Rockstro
PostPosted: Sun Feb 16, 2020 12:15 am 
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Thanks Paddler.

Now can I alert you to what I think is an error in compiling the "all-together" graph? You've added the X measurements of the RH section and foot on to the end of the 208mm LH section, but not subtracted the depths of the sockets from the X measurements in the lower sections. This has the visual effect on the graph of making those junctions seem bigger than they are.

Do we happen to know the tenon lengths (or socket depths)? They can be no greater than 20mm as that is the first bore measurement in each piece. I'd guess at something like 20 and 18mm respectively.

Oh, and a reminder if we happen to have finger hole diameters, so we can try to compare this one with concurrent similar flutes.


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 Post subject: Re: Rockstro
PostPosted: Sun Feb 16, 2020 1:19 am 
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Terry McGee wrote:
Thanks Paddler.

Now can I alert you to what I think is an error in compiling the "all-together" graph? You've added the X measurements of the RH section and foot on to the end of the 208mm LH section, but not subtracted the depths of the sockets from the X measurements in the lower sections. This has the visual effect on the graph of making those junctions seem bigger than they are.

Do we happen to know the tenon lengths (or socket depths)? They can be no greater than 20mm as that is the first bore measurement in each piece. I'd guess at something like 20 and 18mm respectively.

Oh, and a reminder if we happen to have finger hole diameters, so we can try to compare this one with concurrent similar flutes.



No, I did not do that. The sockets are indicated to be 20 mm long. I subtracted the socket length because tenons and sockets overlap when
the flute is assembled, and used the last 20 mm of tenon bore values for the section of the bore that overlaps the socket.

There is, however, a slight visual error in the graph in the sense that the peaks occur at bore length values that are not rounded to the nearest
10 mm, like all the other measurements. If you look carefully at the data you see that all values are taken at 10 mm intervals going down the
bore of each section, except the final value, which is taken wherever the end of that section occurs (208 mm in the case of the top section, and
208+135-20 in the case of the next section.

For reasons of difficulty wrestling with the graphing software, I placed the 15 mm value that occurs at 208 at 210 instead, so the graph plots it at
210 mm, which is 2mm further along the bore than measured. This would not appreciably change anything visually. A bigger issue is that the next
measurement down the bore occurs at the start of the next flute section, which, if the tenon is the same length as the socket, should also be plotted
immediately adjacent to the previous data point. On my graph it is plotted as the next data point 10 mm further along, and there is a line between
those two points. This does not alter the fact that the tenon flares at the end, but it makes the connection to the next section look smoother than
it is, and this accumulates at both joints to make the overall bore length look longer than it is.

By rights, the bore profile should be represented as three separate lines, with one stopping where the next starts, instead of a single continuous line.
Specifically, the value of 14.7 on the graph that follows the peak value of 15 should be right after it rather than 10 mm later. Similarly for the next
peak: the 12.7 value should be placed 5 mm later than it is, and the 12.4 value should be placed immediately after that.

Visually, this would make a minor difference to the look of the graph, making the flare of the tenon look even pointier, but it would not change the fact that these
two tenons have a flare at their end, just like the equivalent tenons of all of the other dozen or so Rudall flutes whose bore profiles have been posted. This is in
contrast to what you would expect from tenon compression, and to what is measured and shown on bore profiles of other flutes, such as your Potter. In all other
cases, when a tenon is compressed the bore under the tenon ends up being smaller than the bore that immediately follows it in the next flute section, that is
not subject to tenon compression. The discontinuity in the bore profiles jumps in the other direction. But here we have the opposite. We only seem to get this
on bore profiles of Rudall flutes, and we get it on all of them, and never on the head tenon.


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 Post subject: Re: Rockstro
PostPosted: Sun Feb 16, 2020 2:20 am 
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If the end of the LH section is 15mm diameter at 208mm along the X axis, and the lower tenon and the RH section socket are 20mm long, and the first bore measurement (14.7mm) in the
RH section is 20mm from the start of its socket, then the 14.7mm should lie directly under the 15mm point, not 10mm to the right.

I became aware of the difference when I plotted your data points and got a quite different looking graph. I'll post it when I've had time to contemplate what it might be telling us and put in my best guess.

(It's always possible I've made a mistake, but we should be able to work that out pretty quickly! As a check-sum, I get 208+135+142-20-20 = 445 for the total length of the conical section. Agreed? "Conical" in inverted commas!)


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 Post subject: Re: Rockstro
PostPosted: Sun Feb 16, 2020 9:45 am 
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Terry McGee wrote:
If the end of the LH section is 15mm diameter at 208mm along the X axis, and the lower tenon and the RH section socket are 20mm long, and the first bore measurement (14.7mm) in the
RH section is 20mm from the start of its socket, then the 14.7mm should lie directly under the 15mm point, not 10mm to the right.

Yes, that is what I said. It would create a discontinuity in the bore line that drops down from the supposedly compressed tenon to the supposedly non-compressed bore section it connects to.
This happens at both tenons, leaving the basic question I have been repeatedly asking unanswered: why is the bore under the tenon end enlarged on R&R flutes.

Terry McGee wrote:
As a check-sum, I get 208+135+142-20-20 = 445 for the total length of the conical section. Agreed? "Conical" in inverted commas!)

Yes.


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