Primer Recurve Bowstrings

The recurve trilogy is the riser, the limbs, and the string.  Without the string, there’s not much of a bow.

Materials

Since archery is an ancient sport, there have been many materials used for bowstrings.  Like many things changed by the chemistry of plastics, modern bowstrings are synthetic and are likely either polyester or polyethylene.  The dominant polyester string is Dacron.  Currently, the polyethylene variant of choice is known as Ultra High Modulus Polyethylene  or (UHMPE).  Three variants of UHMPE that are popular are Spectra, Vectran, and Dyneema.  Many bowstrings are specific blends of different types of UHMPE like Spectra+Vectran.  The synthetic strings have replaced most other types because of their ability to handle different amounts of moisture, wide temperature ranges, and durability.

Creep

The bowstring material provides tension to the recurve limb.  If the material stretches or elongates without recovery, this is creep.  Too much creep can make your bow difficult to shoot or dangerous.  Dacron polyester stretches too much and is rarely used outside of beginner bows.  It’s advantage is that it is highly durable.  A bowstring made out of Kevlar would have very little creep, but is notorious for breaking and is not used by many archers.  The Spectra, Vectran, and Dyneema bowstrings won’t creep for most recurve needs (maybe under very hot conditions like inside a car at an outdoor summer shoot in the desert) and are very common choices for this reason.

Twists

Traditionally, twisting the bowstring has had two purposes.  Non synthetic materials will have an uneven distribution of the bowstring fibers.  Twisting helps keep the bowstring more uniform.  Twisting will also change the length of the bowstring which can be used to counteract the effects of creep and adjust the brace height of the bow.

Modern bow strings are also twisted for the same two reasons, although there is less creep and generally the synthetic fibers are more uniform.

Twist rate (twists per unit length) can also have a significant impact on string performance.   Too few twists will be a higher performance string, but it will be harder to adjust.  Too many twists may cause performance issues and strangely may lead to a string which is more prone to stretching with use.  This is because your hand twisted string will have more unevenness than the fibers of the bowstring and your twists will tighten and loosen.

Brace Height

A modern bowstring can work with a wide variety of twist rates.  Most strings can take anywhere from 20-60 twists.  The key is to match your brace height designed for your bow and limbs.  Fewer twists will make a longer string and a lower brace height with a slight improvement in speed.  More twists will make a shorter string and increase the brace height with a slightly slower velocity and slightly more control.

Strand Count

A recurve bow is all about tension.  The bowstring is the unit of tension.  The bowstring has to be strong enough to provide the tension of the bow and it needs to do that safely.  A single strand for a bowstring will probably stretch or break.  Bowstrings are made up of multiple strands.  How many are the right amount?  The right answer is you should have enough strands to make your bow safe.  That number used to be higher but it is now shrinking due to the strength of UHMPE materials.  The strand count will affect serving choices.

Serving

bowstring-serving-annotated

Your bowstring will likely have three areas of serving.  The end loop serving is at either end of the string.  You can tell the top of the bowstring from the bottom of the bowstring because the top loop is a little larger.  The third area of serving is the center serving.

These two different zones of serving have two different roles and thus can be made up differently.  The end loop servings must be resistant, but cannot be abrasive since they come into contact with the limb tips.  End loop servings create the loop and must tightly grip the underlying string strands to prevent separations, loosening, or fraying.

Center servings connect with your arrow’s nock.  The center serving must yield a smooth and consistent release of the arrow.  The center serving must avoid shifts and changes to prevent the nocking point from suffering variance.  The center serving should keep the same diameter over a long period of time to avoid variance in the nock connection.  The center serving is coupled to your nock size.  Nocks come in different sizes and

Different materials may be appropriate for the two types of serving or it may not matter if you aren’t looking to geek out on your bowstring.  You will definitely to pay attention to the thickness of the center serving since it will be matched to the nocks on your arrows.

Waxing

When archery bowstrings were former cats or sinew from other animals, keeping the string waxed just made sense.  Today’s polymer bowstrings can also be waxed, but you will be looking for a silicone based synthetic wax.  A wax blended with silicone penetrates the string material very well and keeps the inside fibers lubricated as well as the outside.

Waxing includes the two large sections above the middle serving and before the bow loops.  Some of the waxes may need a little heat generated from your own hands running over the strings rapidly to generate friction.  This will help the wax into the material of the bowstring.  Waxing a modern bowstring can help with

  1. Avoid or prevent fiber to fiber abrasion
  2. The wax keeps the strands together and may prevent stray strings from fraying
  3. May extend the life of the string
  4. Prevent water absorption

The frequency of waxing depends largely upon your environment and how frequently you shoot.  Get used to your bowstring and you’ll probably figure out when it needs waxing.

References

http://www.eastonarchery.com/blog/bowstring-tech-tips

http://www.bcyfibers.com/FAQs.php

http://www.archerytalk.com/vb/showthread.php?t=1549354

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s