I received my two Yen Spin today, gold and pink gold.
Great quality as expected
and the ball bearing are not only smooth as butter, but really silent.
The axes slid in and out without locking into the bearing. I could spin the tops like that, as there is a stop on the side of the tip, but I wanted to fixed them, so I looked at the assembly instructions on the website. It suggests slightly nicking the axis with pliers, so the bump grabs the inside of the bearing. But the "slightly" part is no exaggeration. I thought I had been careful but when I tried to put back the one I nicked, I had to press quite hard to install it. Now it's probably installed permanently.
The real bad news is that it's affecting the bearing: that top now spins considerably less than the untouched one if I hold them by the axes.
On the other hand, the spinning times on the table are not affected much, what proves that even for such high-end ball bearings, the friction at the tip (on a hard surface) and the air drag (for such a small top) are much less than the bearing friction. In fact, while on the table it easily spins 5 minutes, on the finger my record was just
15 30 seconds!
My conclusion is that the benefit of a ball bearing is mostly in allowing several starting methods but not in spin times.
Taka did a great job with this Kickstarter and I'm looking forward to the next one.
PS: The top's English name is officially "Yen Spin", not "Yin Spin". Correct this thread's title to facilitate future searches?
Done!
Update:
I could take out the nicked axis and the bearing is working fine. I will probably sand the axle and then use Loctite or a small O-ring to keep it in place.
Update 2:
After sanding a bit the axle (spinning it on a drill), it now fits securely but with little force on the bearing
My spins on the bearing have increased, and now my record is 1 minute on the finger.
Perhaps the bearings need some break in.