I address this question here.

In short, in the later Middle Ages armour and weapons were absolutely the product of specialized Armourers, swordsmiths, brigandine-marks, and mail-makers. Weapons and armor manufacturing and selling was a multinational, highly developed industry that used state of the art manufacturing techniques to make it's product and state of the art financial instruments to fund manufacturing and to sell the finished goods.

Please let me know if you have any follow-up questions.