I received an urgent email from one of my students who discovered that one of the locking screws from the rear of the limb bolt on his recurve bow was missing. He didn’t know how long it had been missing and he had been shooting a great deal so his concerns were twofold: was it safe to continue shooting with that screw missing and how was he to find a replacement?
Top Limb Bolt showing missing locking screw (top), Bottom Limb Bolt (bottom)
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For those of you who do not shoot modern recurve bows, the screw being referred to is a common part on “adjustable limb pocket bows.” Compound people know that turning the limb bolts in or out creates more or less draw weight, respectively. It has only been recently that this feature has been added to recurve bows. A common mechanism designed to accomplish this involved taking the limb bolt and drilling a hole in the very end and tapping it to accept another, slightly oversized, screw. The drilled and tapped end of the limb bolt has several saw cuts made into it and then it is inserted into the bow. Through a hole in the other side of the riser, the “locking screw” is screwed into the newly tapped hole, causing the end of the limb bolt to spread out in its hole, effectively locking it into place.
Compound people don’t have locking screws of this nature (although some models have used a kind of locking mechanism). Because three-piece recurve bows are typically dismantled after every use, they need some sort of locking mechanism, otherwise the limb bolts could move around while the bow was being jostled while traveling in your car. Compound bows are not dismantled after each use and the tension on the limbs tends to keep the limb bolts in place (although it is wise to index then with marks on the bolt heads to show whether they have turned or not).
So, the residual vibration from shooting this recurve bow caused the “locking screw” to wiggle its way out and fall to Earth. (I keep a strong magnet available to find small iron-based parts in the grass. Sliding such a magnet around where one shoots frequently might turn up the missing part.)
Is it safe to shoot without the locking screw? Yes and no. Those limb bolts are often quite tight all by themselves. But if the vibration left over from shots causes the limb bolt to turn, you are changing the tiller setting of your bow which will effect the size of your groups, etc. Nobody wants their bow to give them poorer feedback on how well they are shooting, so, clearly, it is in any archer’s best interest to replace that screw.
Here is where archers have been screwed in the past. It was almost impossible to obtain replacement parts for bows. Local vendors didn’t stock them and even their manufacturers didn’t always stock them. Once a manufacturer has made a “new, improved” model that doesn’t contain that part, they don’t have an incentive to maintain an obsolete parts inventory. When you sell millions and millions of units, you can have a thriving parts industry serving it, consider auto parts stores and restoration auto parts companies as examples. But if you don’t sell millions. . . .
So, I would recommend that archers remove the back screw from the other limb (remember to hold the front screw in place while doing so) and take it down to a good hardware shop to see if they could get a replacement (or two or three if they are cheap). The store should be able to check the threads to see whether they are metric or Imperial/Standard/English/SAE. The bow companies almost never sold spare parts but you may be able to get on the phone with customer service of said manufacturer and talk them out of one. If you had a good relationship with them, you might just get what you want.
In this case it turns out that Lancaster Archery Supply carries the needed part! They also carry replacement limb bolts for Hoyt and Win&Win bows. They aren’t cheap ($49.99 for a pair of limb bolts!) but at least they are available.
Addendum For you history buffs, before the adjustable limb bolt bows were available, people did adjust their bow’s draw weight and tiller but it was a clunkier process. Since limb bolts were just plain bolts, archers would back the limb bolt out (or nor screw it in as far) and then slip tiny wedges, also called “shims,” between the limb butt and the pocket, then tighten down the limb bolt. If you shimmed both sides of the limb butt equally, you adjusted the draw weight of the bow (downward, slightly). If you shimmed the top limb differently from the bottom limb, you were adjusting the bow’s tiller. If you had a larger shim on one side of the limb bolts than the other, you were actually rotating the limb (slightly) which could be enough to compensate for a slight twist in the limbs.
One can argue that the advent of the adjustable limb pocket systems currently available were the result of too many bows being returned to manufacturers when initially bought due to very slight limb twists and tillers being out of spec. With the adjustable limb pockets this small issues could be adjusted out as a matter of course. I suspect that the “spare parts” available in Lancaster’s catalog (Bless LAS!) are there because of so many of them either wearing, or falling, out.