To achieve maximum spin times, there are certain qualities a finger top should have. These include the following: excellent balance, mass concentrated along the edge, the tip being as close as possible to the center of mass, a sharp conical hard tip, a slightly concave hard spinning surface, some lubrication, a light weight core and a knurled spindle.
Here is some information about each of the characteristics:
If a spinning top is balanced well, than there is no side which is lighter or heavier. It is easy for a spinning top to be unbalanced and hard to make one balanced again. Often the problem is either placement of the tip or distribution of weight. To fix unbalance, you can either add or remove weight to one side of the top, or you cans shift the tip. To find which side is heavy, one technique is with a paintbrush. While the top is spinning slowly, hold a fine paintbrush with a contrasting paint to the spindle. The heavier side will lean away, brushing the paint and leaving a mark. Once a few marks are made to indicate the heavier side, one can either shift the tip in that direction or remove weight on that side.
The vast majority of the weight of the finger top should be located as far from the center as possible. This can be achieved by making a dense flywheel. The denser the flywheel, the better. For example, tungsten metal is optimal, although other metals may be more suitable. The shape of the flywheel should be rounded and smooth to limit air resistance.
The tip, on which the spinning top spins, should be located as close as possible to the center of mass. This is to make the top as balanced as possible, whilst maintaining the ability for it to fall over ( a necessary property of spinning tops ). To put the tip so close to the center of mass, you may wish to design a recessed top. This means the tip is actually inside the top. The underside would be deeply concave in this scenario. Examples of this technique can be observed on the finger tops of 'Iacopo Simonelli'.
Type of Tip:
There are 2 main types of tips: spherical balls and conical spikes. Although ball tips are more forgiving and easier to deal with, for maximum spin times, a conical tip is required. The tip should be made of a hard material to reduce wear during spins which would create unbalance. Examples of this include: synthetic ruby and sapphire, tungsten carbide, HSS. Conical tips are usually either tungsten carbide or HSS.
Type of Base:
The base should be concave and of a hard material such as tungsten carbide or HSS. Glass bases get scratched easily by hard tips which reduces spin times. The base must be extremely smooth, preferably polished to around 5 microns or better.
A small volume of lubricant should be used with conical tips. However with round tips, a larger surface area would be in contact with the lubricant, creating a fluid drag. This would harm spin times instead of helping them.
The core of the spinning top should be a light as possible. This is to avoid unnecessary wear on the tip during the spin. Usually, the core is made from either a light metal such as aluminium or magnesium, or a type of wood. Woods are lighter than either magnesium or aluminium, however the metals are more durable.
The spindle is the part you spin with your fingers. By knurling this, the better grip allows a faster starting speed. If the top is balanced well enough, you can spin it multiple times to increase the rpm.