Activate Grinding Station by tapping it and sacrificing Sword of the Meek.
Skittering Precursor triggers, creating a 0/1 Eldrazi Spawn creature token.
When the Eldrazi Spawn enters the battlefield as a 1/1 due to Weapons Trainer, Sword of the Meek triggers, returning Sword of the Meek from your graveyard to the battlefield attached to the Eldrazi Spawn.
When Sword of the Meek enters the battlefield, Grinding Station triggers, untapping Grinding Station.
Resolve the Grinding Station ability, causing target player to mill three cards.