I've been playing a lot of Dark Souls 3 and The Witcher 3, which both have weapon degradation and repair. So I wanted to put a simplified mechanic into my ACKS games. Here's what I've got.
Weapons all have a quality attached to them that signifies how well crafted they are. This is represented by a weapon quality die. Standard quality weapons are a d8 quality, with masterwork/Hattori Hanzo/Damascus Steel weapons at a d10-d12 and poorer quality weapons at a d4-d6 range.
After using your weapon, roll your quality die. On a result of a 1, the quality drops a die step and the weapon gains a -1 to damage rolls. Minimum damage is still 1. When you roll a result of a 1 on a d4 quality die, the weapon is broken and only does 1d2 damage.
Different factors can make the quality roll more difficult. If a character doesn't take a turn to clean and hone the blade with a maintenance kit, then the quality roll will reduce a die step on a result of a 1 or 2. This is cumulative with using a weapon constantly without maintenance. Using a sword for three battles without maintenance would make the roll a 1-3. Other factors that can increase the difficulty include hitting a very hard object (stone, a dragon turtle's shell), leaving a bow strung constantly, or sunder attempts.
ACKS Optional Rule: Instead of the -1 to damage, you can roll on the Scavenging Treasure table on page 210 of ACKS each time your weapon goes down in quality, I'd roll a d16 to ignore the Shoddy Construct and Roll Twice results, since you won't want this weapon breaking so early.
Weapon Maintenance and Repair
Maintenance can be oiling and honing your sword, waxing and unstringing your bow, cleaning your musket out, etc. You can use a repair kit to bring up your weapon's quality die by one step, up to the maximum quality for its type. A repair kit is 7 gold and comes with the tools needed to repair the weapon it's for out in the field one time. Repairing your dinged weapon back to its maximum quality die using a blacksmith is simply equal to half the cost of the weapon. Repairing a broken weapon is just the cost of the weapon.
A maintenance kit is 20 gold. These help to keep the difficulty low when making a weapon quality roll. They are good for five uses, then must be restocked for 5 gold, representing buying more oil or wax or other consumable items.
You could also do this with armor and shields, with the negatives being a loss of AC or Initiative (or just using the Scavenging Treasure table, which I do prefer). Magic items probably won't need to be honed, or maybe they don't need to make the rolls at all. Haven't decided yet, but I think I prefer the former. These rules are meant to add some more depth to my wilderness survival games, where a broken sword can really mean the difference between life and death. But, I still want to keep it simple for myself and my players