All craftmetal locations in Hollow Knight: Silksong
via polygon.com
Short excerpt below. Read at the original source.
Finding Hollow Knight: Silksong‘s craftmetal locations might not be essential, but if you want some of the game’s best tools, like the Cogfly, it’s more than worth the hassle. The most powerful tools require craftmetal, and Silksong isn’t exactly forthcoming with this particular collectible.