Junk Machine

You can't put hammers in the Junk Machine

[4SlotToaster]

The reason for this is because you need a hammer to break the Junk Machine. Nothing else can.
Therefore, when you hit it, it can't produce materials, as it registers as "must break".

Hope I cleared that up for you. Welcome to the forums!

[unfaithful p1nkbr0]

It's the same with shelves and showcases… although you might be able to hex hammers into those.