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[James]

Hi!

It has been a while since I have made a decent spinning top due to DT coursework at school. However, I have finished this and have a little more free time. I finished making this top a week ago, a top which I started months ago.
The flywheel is solid brass. The core and spindle are zebra wood. The tip is a conical tungsten carbide piece housed in a steel screw, which is locked into a brass holder. This way, the height of the tip can be adjusted and it is replaceable. This is the first top where I have tried this method. The base is tungsten carbide as well, held in an aluminium sheath which is stood in a tulip wood base.
The top weighs 130g. It has a diameter of 48mm and a height of 80mm. I can start the top with a single spin of approximately 1100 rpm. With multiple twirls, I can achieve approximately 2500 rpm. I have recently achieved a spin of 28 minutes and 3 seconds - a new personal best!

Here are some images:



The cube is tungsten, 10x10x10mm for scale




This is a picture of the top spinning on my old base




This is a nicer picture of the full top




Here you can see the tip underneath

I have attached a short video of the top and of it spinning.

I will make a youtube video about this top at some point. It will go on my channel: HiPer Spinning Tops. Feel free to tell me what you think!

[Iacopo]

Wonderful !

I never used zebra wood, it looks very nice. 
And the top seems more accurate than your older ones, you are continuing to improve !

I looked at your data and compared them to the mine, they aren't very different.
I don't have 48mm/130 grams tops, but I have some similar, just slightly larger and heavier.
My best starting speeds by a single twirl with them range from 1206 to 1380 RPM, and by multiple twirls from 2081 to 2760 RPM.
I do better than you with single twirls, because my fingers are stronger, but, interestingly, by multiple twirls, we have more similar results; I have six tops similar to this your one, the highest multi-twirl speed I obtained with each one of them is 2453 RPM, 2370 RPM, 2081 RPM, 2453 RPM, 2659 RPM, and 2760 RPM.

This makes me think that you have very agile fingers, because to accelerate these kind of tops to that high speed, (nearly 50 rounds per second !), require agility, very quick but still accurate movements of the fingers, (while by the single twirl pure strenght is more important).  2500 RPM is very good !

I could spin the last two tops to an higher speed because by the time I have improved the shape of my stems;
long stems work better for an higher starting speed, and in fact I see a long stem in your top.
You can make even better if you can find a way to make a knurl for your stem, so to improve the grip for the fingers.
One trick for to improve the grip of the stem, invented by Aerobie, is to glue a piece of sandpaper to the upper part of the stem.
Before to knurl my stems, I resorted to rubbing my fingers with garlic, or even a piece of apple, to have better grip, when I wanted the longest spins.

Also I found that the diameter of the stem influences the starting speed: the best diameter for to have the highest starting speed, for my hands, is 3-4 mm, I believe that very probably it is the same for you.
3-4 mm is referred to a knurled stem.  With smooth stems is probably better to have them a bit larger. 
   
You had a 28 minutes spin starting with a single twirl or by multiple twirls ?

[ta0]

The stem makes it look so tall that's difficult to believe it can spin that long. Of course, that's deceiving as the center of mass is very low. The long stem also makes for a spectacular precession in this type of tops.



Good work!

[James]

@Iacopo,

Thank you very much! I achieved 28 minutes with multiple twirls. With a single twirl, I achieved 15 minutes (also a personal best). The diameter ant the very top is 5mm un knurled. I will knurl the stem at some point using small hand files.

@Tao

Thanks!!!

[Iacopo]

I achieved 28 minutes with multiple twirls. With a single twirl, I achieved 15 minutes (also a personal best). The diameter ant the very top is 5mm un knurled. I will knurl the stem at some point using small hand files.

Very good !  It seems like we have similar spin times by multiple twirls:  I have a 19'01" longest spin with a 110 grams top and a 41'59" longest spin with a 171 grams top.  You are somewhere in between.  Of course heavier tops spin longer.
 

[Jeremy McCreary]

Of course heavier tops spin longer.

Provided that the mass distribution per unit mass and CM height stay roughly the same, drag doesn't increase significantly, and tip resistance doesn't increase too much under the extra weight.

In other words, if you're going to add mass to make a top "heavier", you have to do so very carefully. Iacopo's a master at this.

[Iacopo]

Of course heavier tops spin longer.

Provided that the mass distribution per unit mass and CM height stay roughly the same, drag doesn't increase significantly, and tip resistance doesn't increase too much under the extra weight.

I was too succinct.  I meant that, at parity of used materials and design, in this kind of tops I and James make, heavier (and bigger) tops spin longer.  I find this to be true up to approximately 300 grams, (for tops started by multiple twirls), then, over 300 grams, there isn't anymore further increase, or, at least, significant increase of the spin times. I obtained my absolute longest spin, almost one hour, with a 298 grams top. From there, the lighter the top, the shorter it spins. 

[Jeremy McCreary]

... at parity of used materials and design, in this kind of tops I and James make, heavier (and bigger) tops spin longer.  I find this to be true up to approximately 300 grams, (for tops started by multiple twirls), then, over 300 grams, there isn't anymore further increase, or, at least, significant increase of the spin times. I obtained my absolute longest spin, almost one hour, with a 298 grams top. From there, the lighter the top, the shorter it spins.

Very interesting! Expected from my own top building that spin times would eventually peak at some total mass within your usual design space. But didn't expect a limit as low as 300 g.

For one thing, your tips would eventually start flattening and/or boring into their supports under the weight. (As I recall, you've even posted photos of that process.) For another, if the well-understood aerodynamics of spinning disks are any indication, your drag should increase very rapidly with maximum rotor radius, all other things being equal.

Q1: Do your spin times decline with mass above 300 g or just level off?

Q2: Heaviest top (of your usual design) you've tested? Best spin time?

Q3: Any thoughts/evidence as to why your usual design stops gaining spin time above 300 g?

[Iacopo]

Q1: Do your spin times decline with mass above 300 g or just level off?
Q2: Heaviest top (of your usual design) you've tested? Best spin time?

Best spins, (tops started by multiple twirls):

110 grams = 19'01"
130 grams = 28'03" (James' top)
171 grams = 41'59"
298 grams = 58'19"
656 grams = 57'52"
847 grams = 41'25"(external tip)

All the tops apart from the last one have a recessed tip.
The last one would spin longer with a recessed tip, but still shorter than the 298 and 656 grams tops.
Maybe the longest spins could be with 400-500 grams tops, but I don't think that they would spin much longer than the 300 grams ones.

Q3: Any thoughts/evidence as to why your usual design stops gaining spin time above 300 g?

The best efficiency is not near 300 grams, but, my data say, simply, the heavier, the better, at least up to 847 grams, the heaviest of my tops. At parity of starting RPM, the heavier would spin longer.  But, started with fingers, heavier tops are started with less speed, and if tops are too heavy for the fingers, the starting speed is too low. So the longest spins happen with the best compromise between efficiency, (better with heavier tops), and starting speed, (better with lighter tops).

The amount of energy by which the top is started influences the ideal weight of the top.
If the tops are started by a single twirl, the longest spins are with 150-200 grams tops, approximately.
 

[Jeremy McCreary]

So the longest spins happen with the best compromise between efficiency, (better with heavier tops), and starting speed, (better with lighter tops).

True enough within your usual design space. But finger top designs vary tremendously. In the general case, "heavier" here should be replaced with "larger AMI", and "lighter" with "smaller AMI", as 2 tops of the same weight can have vastly different AMIs, and vice versa. In the end, the only thing riding on weight per se is contact resistance. As we've both learned from experience, to play the AMI vs. release speed trade-off well, you must also pick the right stem diameter, taper, and knurling.

Best spins, (tops started by multiple twirls):
110 grams = 19'01"
130 grams = 28'03" (James' top)
171 grams = 41'59"
298 grams = 58'19"
656 grams = 57'52"
847 grams = 41'25"(external tip)

Thanks for the data. If your masses changed only through density changes, it would be a lot easier to interpret. But I'm sure other things changed as well, and those details could have affected your outcomes. Even small differences in CM height could have major impacts.

[Iacopo]

True enough within your usual design space. But finger top designs vary tremendously.

You are right.  This is a rough interpretation of the available data, approximately valid just for this kind of tops.

[James]

Hi,

Yesterday, spinning the top on a glass table with the tip external (it is mounted in a screw so I can change it's height), the top spun for 21:45, although I think I can increase this to at least 25 minutes with better balancing. I will not have access to my balancing tools until I go back to school and finish my mocks by Jan 14. I balanced the top with trial and error so it was by no means perfect. With a single twirl it spun for 14:31 on the glass. I did not use any lubricant and the conditions were not perfect. I am sure this can also be improved. I thought this information may be useful.

Since the last post, I have knurled the wood spindle. I cut 8 grooves around the top, 3cm long each, using files. @Iacopo I have alsways admired the fine and near perfect looking knurling you achieve on the wood of your tops. How do you do this? Do you use the technique with the lathe that you also use on the aluminium knurls? Or with files? Any tips?

Here are some photos of the knurl from the top view and how the tip can be external.



emily dickinson faith is a fine invention analysis





is aluminum oxide toxic






Merry Christmas!

[Iacopo]

I balanced the top with trial and error so it was by no means perfect.

Hi, James.  In which way did you balance the top ?  By shifts of the contact point, (maybe filing the sides of the tip, as I do), or adding some weight to the top ?

Iacopo I have alsways admired the fine and near perfect looking knurling you achieve on the wood of your tops. How do you do this? Do you use the technique with the lathe that you also use on the aluminium knurls? Or with files? Any tips?

Yes, I use always the same technique, whatever the material of the stem.
For doing this, I use the lathe in an unconventional way;
I remove temporarely the feed screw from the tool post slide, so that the tool post slide is free and I can move it back and forth more quickly, (moving it by the handwheel would take too much time).
I made a knife specifically for cutting the grooves in my stems, I mount it in the tool post as shown in the photo, then, moving the tool post slide back and forth, I cut the grooves, one by one.



I don't keep the way of the tool post slide exactly at 0 degrees but I tilt it a bit, to the same angle of the taper of the stem, plus 0.5 degrees.  If, for example, the taper angle of the stem is 2.5 degrees, I set the way of the tool post slide at 3.0 degrees;
in fact you can see that the grooves are deeper at the right, while at the left they fade away.

For to have a regular spacing between the grooves, I use a little trick, I insert a stick in the gearbox, between the gearbox and one tooth of the main gear of the spindle axis. This marks a fixed position for the chuck.  That gear has 24 teeth, so, in this way, I have 24 fixed positions of the chuck with a regular spacing between each position and the next one.  (This is explained poorly, if it is not clear enough, tell me and I will add an explanatory sketch). 

This also allows me to cut the grooves two times, with my wooden stems;
the first time I cut the grooves in the wood.
Then I cover the wood with a thick layer of epoxy resin, the resin fills the grooves in the wood.
Then I cut the grooves for a second time, removing the excess of resin from the grooves.
The stick in the gearbox allows me to cut the second grooves exactly superposed to the first grooves in the wood.
In the picture above, the shaving is white because what was being removed was resin, not wood.
As I already said in the past, this is labor intensive, but the finish quality is very good:

 

 
 

[James]

Hi!

Thanks for the reply. I was shifting the tip to balance it. There is a slight play with the screw that holds the tip and the brass holder. I would unscrew the nut and re-screw it a few times until (by chance) the tip is centred quite well. When I return to my school, I will use my diamond file cards to file at the tip using the paint brush method to achieve a better balance. Your technique for knurling is very impressive! I may try it one day but it is very complicated. For now, I will be using files.

[Iacopo]

There is a slight play with the screw that holds the tip and the brass holder.

It was the same for me. This is the reason that I started using the taper joint, (which is quite more steady), instead of the screw joint.
But I lost the possibility to adjust the height of the tip.