one of the many advanced technological skills achieved by ancient Bharatiya Engineers.
No workshop today, anywhere in the world, knows how to do this and indeed the casting of seamless metal spheres is regarded as technically impossible. Before they were rediscovered in the 1980s, it was believed by modern metallurgists to be technically impossible to produce metal g
lobes without any seams, even with modern technology.
Seamlessly cast globes continued to be made in Lahore up to the mid 19th century. In 1842 Lala Balhumal Lahuri, a Hindu maker of precision instruments made such a globe for his Sikh patron.

The hollow metal globe was an outstanding technical 'miracle', it being cast seamlessly in one piece and produced by a workshop of precision instrument makers, shocked the world's leading metallurgical experts.
No one imagined that there might be anything extraordinary about the construction of some of these globes with their origins in classical antiquity. The very idea that they could be cast in one piece with no seam was dismissed, as being an impossible feat.

[Note: It's said to be from circa 1630AD inscribed in Sanskrit and Arabic both. It is also possible that this technological wonder is far ancient and Arabic words are just a later edition. One can observe that glyphs inscribed are typical to Bharat.