Changing Recurve Limbs

QandA logoIt is easy to forget how confusing changing limbs on a recurve bow is. Not that long ago, you bought a heavier or lighter set of limbs (of the correct length) and then just bolted them on. Now things are different. Here is just one of the questions I got regarding this topic.

I read on the internet about the SF Premium forged riser, it says 5 turns. But how do I count 5 turns? I’m not sure about that. Thanks, Steve!

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Turns on limb bolts are counted starting from all of the way in. It is also important that you use the same wrench to do this task each and every time (Wrenches have different shapes which means that if you insert different wrenches you can appear to be in different orientations (bolt head to the riser).) So, the limb bolts are released from whatever locking mechanism involved (typically a screw in the back of the bolt) and the limb bolts screwed all of the way in. This is easier done with the bow unstrung. Then insert the wrench, typically we want to line the wrench up with the body of the riser so as to have a reference (in case the wrench slips and falls out), and back the screw out 5 turns (or how ever many you want, always check with the manufacturer’s specs for the maximum number of turns allowed for safety). Then the locking mechanism is reengaged (usually with a second wrench while the first is used to make sure the limb bolt does move when the locking screw is re-engaged.

Here is an ordinary Allen wrench inserted into a limb bolt. The "handle of the wrench is lined up with the riser in a standard starting position. Note also the red pen mark on the bolt head used as a reference mark.

Here is an ordinary Allen wrench inserted into a limb bolt. The “handle” of the wrench is lined up with the riser in a standard starting position. Note also the red pen mark on the bolt head used as a reference mark.

Then the limbs are fitted. There may be problems at this point. I have found limbs to not fit at the extreme positions of the limb bolts from time to time. If this is the case, the limb bolts have to be adjusted back in until the limbs do fit. (By making this limb bolt position change you are changing the angle of the limbs to the riser but the angle change is being made between the limb and limb bolt, too. Hoyt makes limb bolts with “floating heads” to allow the bolt head to rest flat on the top of the limb, for just this reason.

Typically backing the limb bolts out the maximum number of turns reduces the draw weight by approximately 10%. So, 30# limbs would be reduced by 3# to 27#, etc. Realize that this is approximate and can be affected by all kinds of things. For example, a set of limbs labeled 30# isn’t exactly 30#. Each manufacturer has a “tolerance” it allows itself to be “off” from the listed draw weight. 30# limbs might be 29# or even 31.5#. There is also no guarantee that the top and bottom limbs will be the same, but they will almost always be very close (unless a shipping error ocurred!). The 10% “letoff” is only approximate and it varies with limb butt design, actual draw weight, limb bolt design and any number of other variables.

Because of this fact it is always wise to measure the draw weight with the bolts all of the way in and then all of the way out. This then allows you to determine the amount of change per turn of the limb bolts. So, if the difference between all of the way in and all of the way out is 4# and it is 4 turns, then each turn creates or removes 1# of draw weight.

Here is a different wrench inserted into the same limb bolt. Note the different orientation of the wrench handle. To avoid confusion assign one wrench to make all of your limb bolt changes, so you will get used to its orientation in the bolt heads.

Here is a different wrench inserted into the same limb bolt. Note the different orientation of the wrench handle. To avoid confusion assign one wrench to make all of your limb bolt changes, so you will get used to its orientation in the bolt heads.

Compound bows have much wider ranges of draw weight adjustment, often up to 25% of peak weight and with ultra-adjustable bows the range of draw weights available can be much, much wider. This ability to vary the draw weight is the main reason why a wider selection of arrows is possible for compounds over recurves or longbows.

 

 

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2 Comments

Filed under For All Coaches, Q & A

2 responses to “Changing Recurve Limbs

  1. A shooter from my club says he felt his limbs “softened” a bit, and he had to lower his sight at a 2x70m tournament last weekend.
    At our range we practice below a shade and there’s forest like 10 yards aside the range, so it is always cool and bearable during summer…
    Could a very different tournament setting (twice as hot than practice) really do what he says he felt?

    • It … might … as limbs get warmer they can lose a bit of resilience. Also true when they get cold. It depends on the limbs and whether the bows were sitting in the warm sunshine (if so, they can get significantly warmer than the air temperature. Also 70m is a fair distance. Any slight change in launch angle of an arrow just gets worse and worse, the farther the arrow travels. This might not show up at a short distance, like 18m.

      This temperature effect is less with “carbon” limbs than standard fiberglass limbs and less with molded limbs, like Uukhas.

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