Crossbow Building Wiki

Making a medieval-style nut

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The crossbow lock which combines a revolving nut and a separate trigger iron was invented and taken into use during 12th century (Alm 1998: 14). It's structure is explained thoroughly by Payne-Gallway (1990: 95-100) and to a lesser extent by Alm (1998: 14-15). The nut-and-trigger lock was superior to the older and simpler lock mechanism which consisted only of a wooden trigger and a pin which pushed the string from it's socket (see Alm 1998: 9). During 16th century the simple nut and trigger crossbow lock was enhanced by adding a third piece between the trigger and the nut to increase leverage and make the pull of the trigger smoother (Alm 1998: 55). Obviously this was especially useful later in crossbows with very high draw weight which were spanned with a cranequin or a windlass. Later on, until 18th century crossbow locks became increasingly sophisticated (Alm 1998: 56-59).

Making the nutEdit

Historically crossbow nuts were made from several different materials, but usually from horn (Payne-Gallway 1990: 96-97). However, here we cover making the nut from steel. If you wish to use horn or soft metal such as aluminum, bronze, brass or copper for the nut, reinforce the part that meets the trigger with a piece of (preferably hardened) steel.

There are two basic approaches when making the nut from steel:

  • Use one piece of steel
  • Use three pieces of steel

Unfortunately I don't have any pictures from the nut-making process, but textual explanation is at least better than no explanation. To make the nut from one piece of steel you need a length of round steel rod 4-5cm in diameter. Making the nut is a dull but relatively easy job:

  1. Cut a slice from the steel rod, it's width depending on how wide you want the nut to be. That, in turn, is determined by the width of your bolts' rear end and your crossbow's width at the lock.
  2. Bore a hole of 6-8mm in diameter to the exact center of the nut. The nut's axle will go through this hole. For crossbows of 150 pounds or less 6mm steel axle is strong enough. The more poundage you bow has, the thicker the axle has to be. Alternatively you need to make a proper socket for the nut to avoid the need for an axle altogether (see below).
  3. Cut the nut roughly to form using a hacksaw or an angle grinder
  4. Finish the job with and a good flat metal file.

If you don't have thick round steel rod of appropriate size, you can make the nut from three pieces of steel. This process is somewhat more complicated than the previous one:

Three piece nut

  1. Use a punch to mark the centre of nut to a steel plate 1,0-1,6cm thick
  2. Use a pair of compasses to mark the outline of the nut
  3. Bore a 6-8mm hole to the centre of the nut.
  4. Cut the nut roughly to form
  5. Repeat previous steps three times
  6. Attach the pieces together using a bolt and a nut
  7. Grind and file the three pieces together so that they are as close to identical as possible
  8. Remove the bolt and nut and cut each piece to it's correct form. At this point the side pieces will be identical so you can attach them together with the bolt and the nut for convenience.
  9. Round the outer edges of the "fingers" where string touches them.
  10. Attach the pieces together with the bolt and the nut and bore several small rivet holes through all of them. Then rivet the pieces together. Alternatively you can just weld the pieces together, which is probably easier and faster.
  11. Make final adjustments with a file and a piece of sandpaper

NOTE: There are several other articles describing how to make the socket for the nut.

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