A small forge was installed above his private library to indulge the King in his pursuit of this particular hobby. Here there were two anvils and every tool that could possibly be needed was available. As it happened, locks were of a particular interest to Louis. The room was filled with all kinds of locks: common locks, hidden locks and elaborately gilded locks.
The château's blacksmith by the name of Gamin was employed to teach the King all he knew - probably in all secrecy . When he was not with the King he was in charge of all the locks at Versailles. From him we know that Louis was eager to conceal this hobby from his courtiers and his Queen which resulted in the two coming up with countless stratagems for removing and bringing in the anvils. Sadly, Gamin would eventually betray Louis during the revolution.
The court was not very approving of their King's hobby. It was thought to be a profession for the lower classes - not a a hobby for a King. Even Marie Antoinette had the occasional complain about this hobby but for a far more practical reason: the work left the King's hands blackened and he would often visit her without washing them first much to the damage of her furniture.
Louis XVI seemed to have paid them little mind. Instead, he agreed with Rousseau that every man should know a manual craft. Meanwhile, the pamphleteers had a field day making the King's interest in keys and locks a fitting symbol of his ... marital problems.
Once a delegation of professional locksmiths came to visit their sovereign to present him with a special, secret lock. The King insisted on finding the lock himself which he did indeed and when he touched the spring a small dolphin wrought in steel emerged. Louis was delighted.
Even when the royal family had been forced from Versailles Louis refused to give up this hobby. Once in the Tuileries he taught his son how a lock worked and explained the use of the different tools used by the locksmiths - who had come to change the lock on the King's prison door.