Another Example of Archers Getting Screwed

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?

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Top Limb Bolt showing missing locking screw (top), Bottom Limb Bolt (bottom)

* * *

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.

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3 Comments

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3 responses to “Another Example of Archers Getting Screwed

  1. Kristina

    Dear Mr Ruis, thank you for an informative article. I have a query regarding the locking screw. I have purchased a new riser (Gillo G1), and due to manufacturing fault the locking screw at the back of one of the limbs would not unscrew (simply because it is a bit ‘chewed’ and the key does not turn in it); however I have been able to obtain a spare. The question is- is it easy to replace it by yourself or do I have to go to the shop? How do I go about refitting the defective screw that is still in the bolt? ( The nearest shop is far away from me, and I do prefer to repair things on my own; finding this type of information in the user’s manuals has proven unfruitful). However, if going to the specialist is the only option, then I will have to make the trip. Thank you for your advice in advance- I love reading your articles!

    • Hi, Kristina,
      There is no reason you can’t do the job if you have some tools and can use them. This is “simply” a matter of removing the old screw and replacing it with the new. (I like the Grillo people by the way and their products seem quite well designed.) The problem you seem to have is that the socket in the locking screw is deformed, creating a socket that no longer accepts the proper Allen wrench. If this is correct, there is one possible quite simple trick that might get that screw out. You want to make sure that the riser is separated from the limbs so there is no force from the limbs involved. Since the locking screw and the limb bolt are not fixed to the bow, you need two wrenches: one for the front of the limb bolt and one for the rear (the locking screw). The front Allen wrench needs to be held in position so that when we try to turn the back screw, that we do not turn both of them.

      So, here is the trick. It depends on how much extra space there is around the Allen wrench. You may end up using the “normal wrench” or you may need to use the next smaller one in your set. What you do is take a small piece of aluminum/aluminium foil and wrap it around the tip of the Allen wrench and then you press this into the damaged hole. If the normal wrench (with the Al wrap) fits then you may be able to turn the wrench and the screw, thus removing it. (The Al foil takes up the extra space and gives the wrench something to work on.) If you can’t get the “foil wrapped “normal” wrench” in, try the next smaller wrench in your set.

      If this “trick” doesn’t work, there is a tool called a “screw extractor” you should be able to find online. (If you can’t find one, let me know and I will see if I can find one and send you a link to it.) Screw extractors have spiral flutes on then that have threads in the opposite direction to normal screw threads. With normal threads, if the threaded device is turned clockwise the screw threads take the shaft they are on into whatever threaded hole they are in. The screw extractors threads are backward. So, when you turn it counterclockwise (the direction we want the screw to be turned) the extractors flutes dig into the hole they are in deeper and deeper. These screw extractors come in sets because they have to be matched to the size hole they are to work in, so you may have to buy a set but they aren’t so expensive.

      Aw, heck, in for a penny, in for a pound. Here’s an inexpensive set available online (http://www.harborfreight.com/screw-extractor-set-12-pc-61981.html)

      Let me know if you get this job done!

      • Kristina

        Wonderful! Thank you for an in depth explanation and the link ! I will try the ‘foil’ first and see how it goes. Will let you know once I have fixed the problem- most grateful, Mr Ruis !

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