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[Iacopo]

some design directions like the down-and-out mass distribution just become inevitable. Taken to its ultimate conclusion, down-and-out leads directly to the recessed tip and the dense flywheel on a much lower density core. And once you have a recessed tip, you of course need a secure pedestal shaped to let the top do its thing.

This depends on the aim of the maker.
In my case, I decided to develop a design with the aim of the longest spin times, but this is a very particular and uncommon aim, there aren't many tops designed with this aim.  Then, there are many ways for making a top to spin longer, and the maker has to select which solutions to adopt and which not.  The recessed tip for this aim is not an obvious solution like you seem to believe, and you don't find many tops with recessed tip with this aim, in the present or in the past, at the countrary, (apart from the Malay gasing, I don't know any other, do you ?). 
The Maxwell top doesn't have a recessed tip for to spin longer, Maxwell's aims were completely different, in fact even if my design has some random similitudes with the Maxwell top, reality is that my tops have nothing to do with it.
I didn't even know the Maxwell top when I started recessing my tips. 
The story of the recessed tip in my tops is that, while looking for new solutions for improving the spin times, I found in internet that there are Malay spinning tops with the recessed tip, with the exact aim to spin longer.
I tried it and it worked well, it is a simple solution, also it has the advantage that the top doesn't fall down at the end of the spin, but it gently leans on the base, meaning that I can make refined, polished tops, as I like to do, without having to worry too much to scratch them while playing with them. It also allowed me to create objects a bit different from the usual finger tops, so I adopted it.         

[Jeremy McCreary]

The recessed tip for this aim is not an obvious solution like you seem to believe...

By no means obvious. But as I said, make enough tops, and the tops themselves will eventually lead you to this way of maximizing spin time -- unless you see it somewhere else first, as you did with the gasing. Whether you take advantage of it depends, as you say, on your other design priorities.

In any event, Simonelli tops are about a lot more than just the recessed tips. They bring together unparalleled craftsmanship and a breath-taking combination of artistic, scientific, and engineering design features in a way I've seen nowhere else -- even in big collections. Truly originals in that wholistic sense.

No surprise that other topmakers are following your lead. Would be nice if they gave credit. But to be frank, this is the first time I've seen you credit certain gasing for your inspiration regarding recessed tips. Maybe I missed it.

As for Maxwell, read his main paper about his dynamical top some time ago. Don't recall which design motivations he mentioned explicitly, but the relationship between his recessed tips and long spin times certainly wasn't lost on him. Like you, he was a serious and very clever experimentalist. And he would have greatly valued long spin time in an experimental top.

[Iacopo]

..intellectual property theft?

This is excessive terminology, I didn't make any accusations and I am not angry with anybody.
I myself took various ideas from the others, and I feel there is nothing bad if someone takes ideas from me.
For example, if Ortwin wants to adopt the grub screws as I made in my tops, he can do it freely, and I am happy with it.
I may feel just a tiny bit embittered if someone copies from me a whole blend of ideas, and then without acknowledging where this blend comes from, and then making a business with it...

There is a boy in England, James, who likes to make tops like the mine, but this is a particular case.
I feel he sincerely loves my work, he is respectful, open, never malicious. He is talented because it is not so easy to make tops in this way and he doesn't have large means... I am sure he can become a skilled artisan.
I am totally happy with him making tops like the mine.         

https://youtu.be/4s540si0jLU

[Jeremy McCreary]

..intellectual property theft?

This is excessive terminology, I didn't make any accusations and I am not hungry with anybody.

Sorry, I know you don't view others' Simonelli-style tops that way and should have been clearer. Just mentioned idea theft because that can happen in any endeavor. If someone were making close knock-offs of my deservedly high-priced tops and selling them without due credit or permission, I'd be more than a little miffed.

LEGO construction turns out to be really humbling when it comes to precedence, as it allows me to turn wild design whims into test tops with little time and effort. Sometimes the test top even turns out to have some redeeming play value. Some of these ideas seem pretty novel at the time -- and not just because they were being executed in LEGO.

Then reality sets in. "Wait, was that idea really all mine?"

Alas, in my case, generally not. Sometimes I just forgot that I'd seen it before -- maybe in a Grand Illusions video, in some big top collection, or in an illustration in a book like Gould's or Lourens'. Other times, the idea turns out to be just another case of convergent top-making evolution.

Oh well, I can live with, "Kinda cool that it came to me, too."

[ta0]

The recessed tip for this aim is not an obvious solution like you seem to believe, and you don't find many tops with recessed tip with this aim, in the present or in the past, at the countrary, (apart from the Malay gasing, I don't know any other, do you ?). 
The Maxwell top doesn't have a recessed tip for to spin longer, Maxwell's aims were completely different, in fact even if my design has some random similitudes with the Maxwell top, reality is that my tops have nothing to do with it.

I agree, the recessed solution would not have been obvious to a top maker.

And you are right, Maxwell's intention was not to prolong the spin but to study a body rotating around its center of mass (thus without the influence of gravity) for different values of its principal axes of inertia. In particular he wanted to apply it to the movement of the Earth. Here is a link to the paper from 1857 where the famous drawing of the top appears:
https://archive.org/details/scientificpapers01maxw/page/248/mode/2up
But, interestingly, in a very short report from the previous year he already describes the top and he mentions that he uses a: "top of the same kind as that used by Mr. Elliot to illustrate precession."  If I read it correctly, his main contribution to the design of the top was adding the color wheel to determine the instantaneous axis of rotation, in addition to more adjustment screws:
https://archive.org/details/scientificpapers01maxw/page/246/mode/2up
The article from Mr. Elliot appeared on the Transactions of the Royal Scottish Society of Arts, 1855, but it doesn't seem to be online.

I'm not sure which Malaysian gasing you are referring to. Maybe I forgot about them. The giant gasing I know, have a tip that starts recessed but finishes external (like my Simonelli top). The gasing spin to exhaustion on a pedestal but are traditionally first spun on the flat surface of a mount, so the tip cannot be fully recessed. In the last ten years they have started to catch them directly on the paddle, but I doubt the tips are recessed. I guess they will eventually catch them directly on the pedestals, in which case I expect them to be fully recessed.

[Jeremy McCreary]

Just reread Maxwell's 1857 paper  On a Dynamical Top..., and I stand corrected...
1. For the work on visualizing Poinsot's construction, the invariant axis, and the variation of latitude described in this paper, he did indeed adjust the top to put its CM exactly at its contact.
2. He also mentioned in passing that simpler precession experiments could be done in spindulum mode -- i e., with the CM below the contact.

At no point in that paper did he mention doing experiments with the top adjusted to have its CM above the contact. And that's where I went astray.

Now, the device was clearly capable of that last mode. And Maxwell loved his toys -- especially tops. So he must have fooled around with this setup. But maybe that was just icing on the cake.

[Iacopo]

this is the first time I've seen you credit certain gasing for your inspiration regarding recessed tips.

I have reported it, a few times.
Like this one, answering to a question of yours, do you remember ? (The video in the link shows the gasing with the recessed tip):

Iacopo: Taking away all the removable parts on Maxwell's dynamical top would leave something very much like your tops -- at least the ones we've been discussing on the "test" thread. Convergent evolution, or was Maxwell an inspiration?

No, it is the first time that I see this top.  Thanks to Jim in Paris for having posted this, because this top seems so interesting, and thank you Ta0 for the paper of Maxwell, I'll try to read it, and understand something more about the top.

I started recessing the tip in my tops after having seen the more recent design of the Malaysian traditional gasing, which is where my inspiration comes from:

https://www.youtube.com/watch?v=PS78I0TY7sE&list=PLksvI9o_0C0_I_V4M2qxl1JWZAao9ULaB&index=3

This solution permits longer spin times, which is what I was looking for.   The bell shape then is a consequence of the deeply recessed tip, having pushed the concept to the extreme.

[Jeremy McCreary]

I stand corrected again. My apologies. My memory has not served me well in this thread.

[ta0]

At the beginning it shows the flying giant gasing which, contrary to the regular giant gasing uri, are caught in the air and can spin 2.5 hours or half an hour more. With their recessed tips they cannot be spun on the ground.

I guess my memory was not that good, either.

I love how Maxwell had a jab against trying to understand physics purely on deriving equations:

If any further progress is to be made in simplifying and arranging the theory, it must be by the method which Poinsôt has repeatedly pointed out as the only one which can lead to a true knowledge of the subject, — that of proceeding from one distinct idea to another, instead of trusting to symbols and equations.

I find his writings quite clear and surprisingly modern (except for the use of vis viva for kinetic energy x2).

[Jeremy McCreary]

I find his writings quite clear and surprisingly modern (except for the use of vis viva for kinetic energy x2).

Same here!

I love how Maxwell had a jab against trying to understand physics purely on deriving equations:

If any further progress is to be made in simplifying and arranging the theory, it must be by the method which Poinsôt has repeatedly pointed out as the only one which can lead to a true knowledge of the subject, — that of proceeding from one distinct idea to another, instead of trusting to symbols and equations.

Maxwell makes an important point here. Feynman made the same plea in his famous published undergrad lectures. Not coincidentally, he did it in the chapter introducing rigid body dynamics -- the branch covering most of top physics.

But both showed the math, too.

Symbols and equations do have their charms, after all: Symbols provide a useful shorthand -- with the added benefit of meaning only what you explicitly say they mean at the time. Thus heading off a lot of potential misunderstandings. And the equations encapsulate the governing physical relationships in a very direct way -- one that also that brings out connections and insights you might have missed.

I seem to be better off trying to think and understand both with and without symbols and equations. Too bad I'm no good at writing about the top engineering that so interests me without math.

[Iacopo]

This morning I found a new one:

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