The aim of all these production quests is to teach you to have (at least a small) surplus on every level of the production chain.
This to help you in the future from having smelters and workshops constantly complaining from lack of raw materials.
To have a production of "at least 0" means you must have a surplus, not that you must shut everything down to get exactly 0.
Thus...
- if your mines do not supply enough copper ore for your smelters, build another mine.
- if your smelters do not supply enough bronze for your workshops and toolmakers, build another smelter (or upgrade an existing one), and return to point 1.
- if your toolmakers do not supply enough tools for the quest, and you do not want to produce more, buff your toolmakers.
You may of course also buff all mines and smelters as well, and thus get the quest fulfilled.
But that won't help you or teach you how many mines your smelters need or how many smelters your workshops need.
Walking distances also play a role of course... if possible, try placing your smelters a little closer to a storehouse and your workshops and toolmakers a little (not miles) further away from the storehouse.
