Inconsistent amount of resource to repair items

The bug

When repairing a shovel, 4 corresponding items are needed. When making a pickaxe, 3 corresponding items are needed, and when repairing, 4 items are needed, so I deduct from this that the repairing penalty is 1 item.

A shovel only needs 1 item and repairing still needs 4 items, so the penalty is suddenly 3. The same goes for swords, which need 2 items to make and also 4 items to repair.