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[Bob Gunther]

Hi all -

The mail carrier came today with 100 carbon steel and 10 ceramic bearing balls! So I got to work straight away and here is the result. A maple finger top finished in beeswax and mineral oil. The bearing ball was glued in using thick CA glue (super glue). Any and all reviews, comments, criticisms welcome!

Bob










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[mailman]

I love it!  Simple, understated, and elegant.

How well does it spin?

[mailman]

Also, it's hard to tell from your photos, but how big is it?

[Jeremy McCreary]

Elegant indeed -- and quick! Would love to hear some stats:
Mass?
Rotor diameter?
Rotor length at outer edge?
Rotor center height above tip when vertical?
Best spin time by hand?
Best launch speed?

[Bob Gunther]

Ah yes ... got too excited and forgot to put the measurements in. So the bearing ball is 1/4" (6.35 mm) and the top stands about 2" (5 cm) with a width of 1 5/8" (4.13 cm). It weighs about 13 grams. Spin time is about 64 seconds. I am going to try to balance it as I have seen in Iacopo's video as it wobbles a bit and starts to get a bit jerky after about 30 seconds.

[Bob Gunther]

Elegant indeed -- and quick! Would love to hear some stats:
Mass?
Rotor diameter?
Rotor length at outer edge?
Rotor center height above tip when vertical?
Best spin time by hand?
Best launch speed?

  - Oh boy ... my newbieness is showing ... what's rotor? And launch speed? And how are these things measured?

[mailman]

My understanding is that the widest part....the body of the top....is technically the rotor.

I would guess the launch speed would be measured with a digital tachometer, perhaps infrared?

I'm certainly not a spin science expert, but I know a great looking top when I see one....

[Jeremy McCreary]

Elegant indeed -- and quick! Would love to hear some stats:
Mass?
Rotor diameter?
Rotor length at outer edge?
Rotor center height above tip when vertical?
Best spin time by hand?
Best launch speed?

- Oh boy ... my newbieness is showing ... what's rotor? And launch speed? And how are these things measured?

  No worries!  We were all newbies once. I see now that you've already given most of this info, but just to be clear...

Rotor: Like mailman said, the widest part of a finger top, with a "stem" for the fingers above and a "tip" for the ground below. The rotor carries most of the top's mass and even larger shares of the moments of inertia (see Wikipedia page) about the spin axis and tip. And since it generates most of the top's aerodynamic drag as well, the rotor effectively controls every aspect of top behavior, including spin time.
Rotor diameter: Diameter at the widest part, taken perpendicular to the spin axis.
Rotor length (aka thickness): Representative rotor measurement taken parallel to the spin axis. Since there are no clear stem-rotor or rotor-tip boundaries in this case, it would be reasonable to take the length at the rotor's flat outer edge.
Rotor center height: Distance from the tip-ground contact to the geometric center of the rotor, taken along the spin axis. The rotor's center generally won't be far from top's overall center of mass (see Wikipedia page).
Launch speed (aka release or starting speed): Angular speed of the top when the fingers finally leave the stem. As mailman suggested, this is usually measured with a cheap laser tachometer (see Amazon).
Best spin time: Longest elapsed time between launch and "fall". Knowing when to start the clock is easy. In tops that don't fall abruptly, it's reasonable to stop the clock when the wobble gets severe or when the rotor first scrapes the ground. Smartphones have good stopwatches.

And 2 important stats I forgot to ask for...
Total mass: Around here, usually in grams.
Total length (or height): Distance from tip contact to the opposite end of the stem.

This language is by no means universal, but it will generally be understood.

[Iacopo]

Nice top, Bob !
Certainly it is not designed for long spins, but I like its simplicity, and the clean realization.
It seems like you have experience working with the lathe.

[Bob Gunther]

Nice top, Bob !
Certainly it is not designed for long spins, but I like its simplicity, and the clean realization.
It seems like you have experience working with the lathe.

Thanks Iacopo! I have already decided to make another, this time with a denser wood for the rotor (Nanciton) and a lighter wood (Soft Maple?) for the stem and tip. The stem/tip will be one piece that is bored through the rotor. I will also sink the bearing ball a little deeper, beyond centre and use epoxy to hold it in place.

As for the lathe, I'm no expert but I know it quite well.

[Jeremy McCreary]

I have already decided to make another, this time with a denser wood for the rotor (Nanciton) and a lighter wood (Soft Maple?) for the stem and tip. The stem/tip will be one piece that is bored through the rotor. I will also sink the bearing ball a little deeper, beyond centre and use epoxy to hold it in place.

Sounds like you're headed toward a longer-spinning mass distribution. I'd just like to congratulate you on the current top's excellent aerodynamics. Drag is a key factor in finger top spin time.

In designing a low-drag top, it's handy to have a mental picture of the 3 main large-scale air flows stirred by a typical finger top at speed. You may have one already. If not...

A spinning finger top is effectively a viscous centrifugal pump with all of its outflow (Main Flow 1/3) emanating more or less horizontally from the rotor edge. You can easily feel this outflow on your hand. But you can't have a steady outflow without a steady inflow. A finger top's  primary inflow (Main Flow 2/3) swirls down onto the rotor from above. There will also generally be a swirling inflow from below (Main Flow 3/3), and it can be significant in tops like yours. I'm guessing that both inflows are very happy to follow this top's streamlined profile on their way to the rotor edge.

This brings up an effective strategy in the fight against drag: Go with the flows. Let the inflows merge smoothly into the outflow with the least possible interference from the top's solid surface. And keep an eye out for interference drag, which arises when incompatible flows try to occupy the same space at the same time. Your current top does a great job on both fronts. So do Iacopo's.

[Kirk]

You can't go wrong with the look of maple in my opinion.  You have a nice looking top.  Double fun can be had as it looks like you could spin it on the stem with a finger snap or in the more conventional way.

[Aerobie]

I hope the maker won't be insulted by frank comments.  I only mean to help him with the comments below.

Most people value tops by how long they spin.  To achieve long spin, it's desirable to minimize central weight and maximize perimeter weight.  Iacopo and I have made tops with wood centers and metal perimeters.  They retain the beauty of wood and best employ the outstanding property of wood, which is light weight.  Of course we prefer metal perimeters, especially heavy metal like brass.  But you might want to consider stone or marble perimeters if you desire natural materials.

Keep turning.

Alan

[Jeremy McCreary]

Double fun can be had as it looks like you could spin it on the stem with a finger snap or in the more conventional way.

Same thing occurred to me. The videos below demonstrate the underhand twirl with its palm-up snap of the thumb and middle finger. It's easy to learn and delivers exceptionally high launch speeds in small tops with favorable stem/tip diameters. Since the small tops below were meant strictly for underhand use, their tips are also their stems.

I get the most energetic spins with the 4.8 mm stem diameter used below. I later discovered that this top is even more entertaining with a longer stem/tip and higher rotor -- i.e., more like Bob's top would be standing on its stem.



The 10 mm ball tips on the first underhand tops shown here promote travel in broad closing spirals just predictable enough to make target shooting interesting. The 6 mm tips introduced at 2:17 promote straighter but more erratic travel paths.

[Kirk]

I hope the maker won't be insulted by frank comments.  I only mean to help him with the comments below.

I hope the commentator won't be offended by my comments
A top that spins for 10 or 30 minutes, while technically amazing, is so boring.  Grass can grow in this amount of time.
Then again I was never fascinated by fishing. So it might be me.