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[Jeremy McCreary]

But, in retrospect, I can say that this was one of the purchases that made me most happy.

The day you purchased that lathe was a very good day for all of us, my friend.

[Iacopo]

my experience with tops of many shapes and sizes makes me think that a smaller copy of Nr. 30 might stay up longer.

Yes, you might be right. This is something I will want to try, one day. 

Of course, this does not count for a record. The "top" does not topple and spins down to zero. Therefore it's not working as a real top, at least not towards the end.

Not to topple down is a strong advantage for the spin time. I calculated that my Nr. 30 could spin for approximately 50 minutes instead of 36 if it wouldn't topple down.

The Kemner top in the video, in the last minutes, spins slow enough that it is possible to see what is its spin decay:
it loses , on average, 23 RPM per minute in the last 6 minutes.
My tungsten top loses 10 - 12 RPM per minute during the last minutes of spinning.
But, being littler, the Kemner top supposedly was started at a quite higher speed than the mine.
Difficult to judge.

One of my customers has exactly that same top, and he can hit with it around 10-15 minutes max. only.
He is not bad at spinning, because he can spin my tops for 40 minutes or so.
The others that got the same Kemner top can't reach 20 minutes spins with it, he says.
49 minutes is so much longer, so I don't know what to think. One day I will try making a little tungsten top to see how it behaves.

[Jeremy McCreary]

What is the Kemner top made of? The stem and rotor look to have been cut from a single piece of aluminum or satin-finished stainless steel.

What about the tip? Guessing all those long sleeping spins have worn a small flat at bottom dead center.

[Iacopo]

What is the Kemner top made of? The stem and rotor look to have been cut from a single piece of aluminum or satin-finished stainless steel.

What about the tip? Guessing all those long sleeping spins have worn a small flat at bottom dead center.

The flywheel is made of tungsten.
The core and the stem are of aluminum.
It weighs 51.2 grams, and it has a ceramic ball tip.
The diameter is maybe 33 mm, less or more.

The name of the top is "Dynamo".
In the Kemner site there is written about this top:

"The top weighs in at 51 g.  It has reported spin times over 20 minutes. 
Due to the inherent issues with tungsten the top may have some flutter near the end of the spin even after being balanced."

[Jeremy McCreary]

"Due to the inherent issues with tungsten the top may have some flutter near the end of the spin even after being balanced."

Thanks! Wonder what that statement from Kemner means? Do tungsten's high density and difficult machinability limit the ability to fine-tune balance, centering, or alignment?

[Iacopo]

Thanks! Wonder what that statement from Kemner means? Do tungsten's high density and difficult machinability limit the ability to fine-tune balance, centering, or alignment?

I believe that the tungsten they use is not pure but an alloy which is not very homogeneous, then they balance it making holes under the top, so, while correcting the static unbalance, they may cause a bit of dynamic unbalance ...

[ortwin]

Thanks! Wonder what that statement from Kemner means? Do tungsten's high density and difficult machinability limit the ability to fine-tune balance, centering, or alignment?

..., then they balance it making holes under the top, so, while correcting the static balance, they may cause a bit of dynamic unbalance ...

See, that is what I mean: if there would be setscrews for  dynamic and for static balance one would have a chance to correct this in a more elegant way. Also a ring on the upper surface prepared with regard to be useful for "the balancing by laser" method would be nice in these tops that are meant to spin for a long time. I can't believe all those tops are perfectly balanced and still show such a big difference in spin time.

With the difficult machinibility and all of tungsten, why not using something different? It does not have to be gold, platinum is a lot cheaper these days and also it has a higher density. I do not know about machinibiity though.  Don't you think you can easily find a collector amongst your customers willing to finance such a project?

 Of all those Kemner tops for example with times from <25 minutes to >40 minutes, do you know if the same person had two spinning on the same surface for very different times? Or could it also be on the other hand that different persons use different bases that also could account for a part of the differences? I recall with my Euler's Disk I got far better times when I glued my base to the floor......
 

... Have you considered to buy a lathe ? 

No Iacopo I really don't consider buying a lathe. I know people who either own a lathe or have access to very good ones. I think I could ask them for a favor one day I have a good plan..... 

 Actually my favorite top would be a set where you can balance the top static and dynamically by set screws, you would have tips of different material and diameter to choose from, different interchangeable stems, tip height could be adjusted and finally also different flywheels (material, dimensions) could be fitted. Size about as large as the Quark top. Anyone here willing to make a good offer ??    

Jeremy, you wrote:"... But air resistance, another powerful limit on spin time, may well favor smaller tops. Many tops have disk-like rotors. Consider, then, the swirling air flow induced by a thin smooth spinning disk of radius R.

The resulting aerodynamic braking torque generated by the disk face grows with R⁴."

Do you think that (3) spokes going out to the flywheel would make considerable improvement compared to a disk?

[Iacopo]

With the difficult machinibility and all of tungsten, why not using something different? It does not have to be gold, platinum is a lot cheaper these days and also it has a higher density. I do not know about machinibiity though.  Don't you think you can easily find a collector amongst your customers willing to finance such a project?

 Of all those Kemner tops for example with times from <25 minutes to >40 minutes, do you know if the same person had two spinning on the same surface for very different times? Or could it also be on the other hand that different persons use different bases that also could account for a part of the differences? I recall with my Euler's Disk I got far better times when I glued my base to the floor......

Someone asked me to make a large size gold top, long time ago, but I refused; to work with such an expensive material would have made me nervous.  I am not rich, what if something went wrong ..?  The most bizarre request I received was for an uranium top, but I don't know if this was a serious request, I refused right away. Platinum is still too much expensive.  If someone wants an expensive material, I am willing to consider silver, its density, about 10.5, is good, not far from that of lead, and the cost not so intimidating.  Sometimes I used lead, or tungsten alloy, when I wanted the longest spin times.  I developed a good method for balancing my tops so I have no problems using inhomogeneous materials like wood or tungsten alloys.

One reason that the Kemner top of George spun for so long is that that top didn't topple down but continued to spin until stopping, in vertical position.  This happens when the tip is worn out and a tiny flat surface has developed at the contact point, so that the top can stay upright even while not spinning, balanced on it.
I don't know what bases exactly were used and how much this could contribute to the difference between the spin times. Usually concave glass mirrors are used. Lubrication could make some difference too.     
     

[Iacopo]

Burning desire department: Gee, wish Iacopo hadn't mentioned uranium. Now I want a U top! Yes, even depleted U has some residual radioactivity. And U is both combustible and very hard to put out. So a lead-lined fireproof storage bunker well away from the house might be in order. 

I think I can say it...  The person who asked me such a top is Andrew Baer; his grandfather was Hugo Gernsback, known as a father of the science fiction.
Mr. Andrew wanted from me a really very special spinning top for to commemorate his grandfather.
We had a very long correspondence, five years ago. 
He asked for an uranium top, probably he was joking... but I am not so sure, he seemed to love the idea.
Another his idea was to have a diamond spinning surface, because of the very low friction, (he wanted extremely long spin times). His father was jeweler. I explained him that the spinning surface had to be concave. He tried if it was possible to have a concave diamond, but it turned out that it is impossible to cut a diamond in that way.
He also asked for replaceable tips, which I refused to make, because at that time I believed that it is impossible to have replaceable tips and perfect balance.
In the end, I didn't make any top for him.  But he partly contributed to the development of my design, because some time later I considered more seriously to have replaceable tips in my tops, and now practically all my new tops have them.

[Jeremy McCreary]

Jeremy, you envision a small version pf this bicycle wheel with a stem ?
Or maybe without a stem? There must be some crossover point (regarding the diameter) where a top is spinning longer when spun with two hands and without a stem as opposed to the same top with a stem that brings up the CG higher.

Yes, like that bike wheel. Wonder what the optimal profile for the missing outer flywheel would be? Semi-circular, half-ellipse, some kind of ridge?

Also my "Amazon purchase"  comes to mind:

Only one  spoke. The Spoke (a streamlined version of course) and the ring inside the platinum flywheel could be 3D printed .

Very cool design concept.

The tops you show in your pictures look great. Do you get your inspiration more from Star Wars or rather from 2001: A Space Odyssey ?
That "modular building system" results in quite large tops, right?

Most of my inspiration comes from the totally cool mothership currently orbiting behind the moon. Our moon.

Seem like nice folks. From Zargon IV, they say. But I'm pretty sure they're gonna eat us.

[Jeremy McCreary]

@ta0: On closer look, the bicycle wheel spokes seem to have reinforcing ridges that the top wouldn't need for strength and would be much better off without aerodynamically.

Agree about the crossover point, but there's a 3rd alternative: A detaching stem that you pull away to release the top. I've had good luck with both dog and centrifugal clutches in this regard.

You'll see what I mean in the first minute...

[ortwin]

Yes, I guess the detachable stem would work, but you have a second piece of equipment.   It is in a sense like using the ribbon method to start the top. But with the string you reach farR higher RPMs.
Of course it is no official contest with official rules, everybody like me can make his own rules. Like, no recessed tip, only one twirl, only one piece....
To continue the list of possibilities:
- no lubricant
- flat surface
- glass surface
- only one hand allowed to start the top
....

Probabely I am just picking the set of rules so that I   have a niche where I think I have the chance of achieving  something. Of course that process can look quite arbitrary.  Anyways, at the moment, .....no recessed tip, only one twirl, only one piece... is what I personally like to go for.

I am also guessing that the Kemner tungsten Dynamo top being only  33 mm in diameter is close to that crossover point we discussed.

[Iacopo]

It has been my guess for a while that a platinum wheel with 3 needle spokes would have the absolute longest duration possible.

For the spokes, note that a circular rod moving sideways through the air generates a lot of drag -- partly due to its complex turbulent wake. Best for the spoke coming behind to see as little wake as possible.Think of how racing bicycle frames have evolved.

I like the idea of three very thin spokes.  Probably there is no need to make them flattened because the air flow seems laminar at the typical speed of spinning tops, in which case having the littlest surface exposed to the air is an important factor relatively to have streamlined shapes.
The top with a single spoke is elegant, but a single spoke should be quite robust for to have sufficient stiffness, while three spokes could be very thin.
 

[ta0]

Probably I am just picking the set of rules so that I   have a niche where I think I have the chance of achieving  something. Of course that process can look quite arbitrary.  Anyways, at the moment, ..... no recessed tip, only one twirl, only one piece... is what I personally like to go for.[/font]

I think your rules are very reasonable and among the most logical to have for a record, so not too arbitrary.

Now that was an inspiring remark for me! Especially the word "needle". I remembered these pins with the yellow glass head my wife has in her sewing set. When I looked for them I also found these white plastic rings - they are used for curtains or something.

That's a nice homemade top! It reminds me the exclamation point top minus the stem.
But I don't think that a single spoke top could be made balanced and rigid enough to go for a record. I think 3 spokes would be the minimum.

[ortwin]

It reminds me the exclamation point top minus the stem.
But I don't think that a single spoke top could be made balanced and rigid enough to go for a record. I think 3 spokes would be the minimum.

It also reminded me of the exclamation point top when I had it spinning for the first time. We could call this one "PERIOD."


I do not see a problem with balance with only one spoke. Remember, I insist on setscrews . Also I have some other small ideas for that. Rigidity is not a big problem, I would say, since you don't twirl it by a stem. The largest problem that I see, is to get a good tip attached if the glass of the needle proves to be of insufficient quality.