Ok, I would have never searched for the volume tool in the arch workbench.
+1 to shift it to measurements.
I thought I share a bit more technical information about development of the spinning top. IMHO this part has a few interesting points.
This is the first iteration of the design in FreeCAD. If you want to see a picture of the real thing (It's ugly!) I recommend having a look at the prototypes gallery athttps://www.kickstarter.com/projects/1246976965/the-wozz-a-truly-amazing-spinning-top-with-a-twist/
The fly wheel is mounted onto a ball bearing (shown in green) which in turn is mounted onto the axle/handle (shown in orange). A string can be wound onto the spool on top of the fly wheel. When the user holds the axle in one hand and pulls the string, the flywheel starts to spin on the ball bearing while the axle is kept stationary.
My first thought was that to achieve full behavior of a spinning top (where fly wheel and axle spin as one) I need a 'connector' to block the axle inside the flywheel. That's what the strange object above the fly wheel is for. The idea was to drop this connector over the axle into the cone-shaped opening of the rotating fly wheel. On its way down the prongs on the connector would eventually be stuck between axle and fly wheel and would thus block the axle inside the fly wheel.
Well, it turns out this idea is pretty crappy: the necks of the prongs need to be really thin so that the weight of the connector is sufficient to make them bend and adapt to the axle. In reality they would need to be so thin that they would break easily. Or the connector could be extremely massive to put enough force onto the prongs. However the spinning top would then become top-heavy and wouldn't spin nicely anymore.
Luckily the connector isn't needed at all: the friction in the ball bearing (even in a bearing of very high quality) is way higher than the friction between the tip of the axle and the underground the top is spinning on. So what happens when you spin up this top and put it on a hard surface is that at first the fly wheel rotates around the stationary axle. The axle then quickly gets dragged along by the frictional force in the ball bearing and spins at the same rate as the fly wheel after only one or two seconds: voila, the behavior of an ordinary spinning top. Sounds nice, too!
It was clear from the beginning, that the tip of the top needs to be exchangeable. With the top spinning at high speeds (several thousand rpm) even very hard materials degrade quickly.
At first I thought about using bearing needles with rounded ends as tips: hardened steel in standardized geometry with extremely tight tolerances - perfect! It turns out everything about these needles is well defined and controlled to exacting standards - except for the rounded ends. These are just 'as is' and one can find all kind of variation here. However, the tip of the top needs to have a perfectly symmetric shape, otherwise the top will wobble badly. So bearing needles fall flat.
That's why the second design utilizes a hardened steel ball (from a ball bearing) as tip: these are also standard parts, available in extremely good quality for reasonable price. Furthermore they feature a near-perfect symmetric shape which can easily be centerd in the tip of the top - another very important point. To make the ball exchangeable a small cylindrical neodymium magnet (small bright yellow rectangle on the right side in the picture above) is incorporated into the lower end of the top. The magnetic attraction (most ball bearing balls are made from magnetic material) is strong enough to hold the ball in its bed for all but most extreme bumps. At the same time the ball can be easily extracted with another magnet and swapped with a new one.
Why this is a good idea is visible from this picture:
The ball on the right side is a pristine bearing ball while the one on the left was used as a tip for a few hours. With these defects on its surface it's not yet useless but spinning time is noticeably down.
Else the spool went from the top of the fly wheel to it's bottom. This way the diameter of the spool could be made smaller, which is important to reach the highest possible spinning speed. Also the handle was made bigger to give a more convenient grip (roughly the size of a pencil).
This iteration of the spinning top still features an axle going all the way through the fly wheel. In later iterations the axle was shortened to end inside the fly wheel and the lower tip of the spinning top was formed formed onto the fly wheel. This is because when the spinning top is dropped while it is spinning it will keep its orientation and will hit hard right on its tip. This gives an extreme shock for the ball bearing (the tip is pretty sturdy) which leads to the balls in the bearing punching little dimples into the groove they are running in. Not pretty!
The final version has a few more details and refinements I would like not to share at this moment, but from the principle it is pretty close.
All in all this was a fun project, both from the design work involved as well as from the result.