This article describes a simple push-trigger crossbow with a wooden bow. The stock design is 15th century style (see Harmuth 1986: 90-91), so this is not designed to be a realistic "period" bow. At that time heavy crossbows with steel bows were already in wide use.
The full CAD drawings are available here:
If you have any questions, please send mail to my Google mail account (samuli.seppanen).