Crossbow Building Wiki

Plan for a simple leaf-spring prod[]

I usually make my bows around 80-90cm in length, because bows of this length are still relatively manageable and light yet allow relatively long draw and high energy storage. The width at the center is usually 40-50mm and 6-8mm at the tips, depending on the bow thickness. The rationale for these thin tips is described here.

The bow described here has the following dimensions:

  • 900mm long
  • 6,2mm thick
  • 40mm wide at the middle
  • 6mm wide at the tips

It tapers linearly in width. Draw length is 40cm for a bow that's deflexed slightly (~45mm). Draw length could be safely increased by at least 2-3cm, but it's better to play it safe if you're making your first bow. The bow will draw ~150 pounds (~68kg) at 40cm draw. A bow of similar dimensions but 8,2mm thick seems to give draw weights of ~300 pounds, making a cocking device necessary.

Plan of a typical pyramid-shaped steel bow

As you can see from the plan, the tips are raised slightly so that the bowstring is above stock when the bow is at rest. An alternative approach is to cant the bow slightly upwards when you attach it to the stock. In either case, the idea is to avoid the bowstring from pressing against the stock during release, thus wearing out quickly and wasting lots of energy.

As shown in the plan the middle part of the bow (20+20mm) is of uniform width (40mm). This makes the bow easier to align with the bow irons and the stock. It does not affect performance as the middle part bends only a little if you use a strong stirrup with bow irons. If you use other kinds of bow attachments then you should omit this slightly narrower middle part for safety. If your bow is made from an actual leaf spring, you should make sure that the center hole is in the exact middle of the bow. Also make sure you leave the holes at the end of the leaf outside the bow. These things may limit the length of the bow, so preferably get a leaf spring which does not yet have the holes punched or drilled into it.

If you're making your first bow, you should definitely make a simple model bow out of cardboard, wood or plastic before you start making the real one. It's easy to spot silly mistakes when you have a model at your disposal. If you have to deviate from this plan, you should first understand the basics of bow design. You should also understand the risks involved in using steel as a bow material. Practical instructions on how to actually make this bow are available here.

WARNING: A common misconception is that a (leaf-spring) bow that's narrow at tips is somehow dangerous, although the exact opposite is actually true; aggressive width tapering makes the bow safe, as stresses of stretch and compression are more equally distributed along bow's entire length. A bow with wide tips (and no thickness tapering) is strained most at the middle and will break there if drawn too far, with potentially fatal results.