ASTM F1880-09

Standard Test Method for the Determination of Percent of Let-Off for Archery Bows

ABSTRACT
This test method covers procedure to determine the percent of let-off for archery bows. Percent of let-off shall be determined from formula using force-draw curve. Other factors for percent of let-off determination include hysteresis effect and rating conditions.
SIGNIFICANCE AND USE
It is recognized that certain designs of the cams used in the compounding systems of archery bows cause variation in the percent of let-off with change in draw length, draw weight, or both. This is true particularly with the style of cam that achieves draw length adjustment by effectively altering the length of the shooting string by any of several methods. In this case, the mid-draw length and the maximum draw weight obtainable (but not to exceed the maximum rated weight of the bow) shall be used to determine the official percent of let-off for the bow in question.  
Historically, two methods have been in use to establish the percent of let-off for archery bows. The most common method uses the peak draw force and the minimum holding force read from the force-draw curve to calculate the percent of let-off. The second method uses the peak draw force from the force-draw curve and the minimum holding force from the let-down curve for this calculation. This test method defines the two methods and distinguishes between them.
SCOPE
1.1 This test method covers the procedure to be used to determine the percent of let-off for archery bows.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Oct-2009
• ICS: 97.220.40 - Outdoor and water sports equipment
• Technical Committee: F08 - Sports Equipment, Playing Surfaces, and Facilities
• Drafting Committee: F08.16 - Archery Products

Relations

• Replaces: ASTM F1880-98(2004) - Standard Test Method for the Determination of Percent of Let-Off for Archery Bows
• Effective Date: 01-Nov-2009

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: F1880 − 09 AnAmerican National Standard
Standard Test Method for the
1
Determination of Percent of Let-Off for Archery Bows
This standard is issued under the fixed designation F1880; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope force-draw characteristic and simplifies the inclusion of let-off.
In general, it is normal for compound bows to have greater
1.1 This test method covers the procedure to be used to
stored energy than conventional bows for a given level of peak
determine the percent of let-off for archery bows.
or maximum draw weight.
1.2 This standard does not purport to address all of the
3.2.4 draw, n—to move the shooting string of a bow from
safety concerns, if any, associated with its use. It is the
the rest or brace position toward the fully drawn position by
responsibility of the user of this standard to establish appro-
applying force to said string. Such action causes the limbs of
priate safety and health practices and determine the applica-
thebowtobendandstoreenergy.Movingthestringfrombrace
bility of regulatory limitations prior to use.
height to the full-draw position corresponds to the draw cycle
of a bow.
2. Referenced Documents
2
3.2.5 draw force, n—that level of force necessary and
2.1 ASTM Standards:
coincidental with drawing a bow to a specific position within
F1832 Test Method for Determining the Force-Draw and
its ATA actual draw length.
Let-Down Curves for Archery Bows
3.2.6 force-draw curve, n—the curve obtained when the
3. Terminology
draw force is plotted versus the ATA actual draw length for a
3.1 Acronyms: given bow.
3.1.1 ATA—Archery Trade Association
3.2.7 full draw, n—the position in a draw cycle of a bow
3.2 Definitions: from which the string of the bow is released and the force
applied to the rear of the arrow to commence the launch. The
3.2.1 ATA actual draw length, n—distance from the bow’s
string at the nocking point location, while at the bow’s full full-draw position of individual archers will vary due to
personal physical characteristics and shooting style. Archery
draw condition, measured perpendicular to a vertical line
3 1
through the pivot point of the bow grip, plus 1 ⁄4 in. (+ ⁄4,– bows are specified as to the range of draw length that they will
0 in.). accommodate to permit archers to select a size that will fit
them. Precise draw length is less of a factor on conventional
3.2.2 brace height, n—the distance in inches or millimetres
bows as compared with compound bows, since it is ideal to
from the shooting string of a bow to the pivot or low point of
match the draw length of the archer to the position of
the hand grip, measured perpendicular to the string at the
maximum let-off in the draw cycle of the compound bow. The
un-drawn condition.
position of maximum let-off for compound bows usually is
3.2.3 compound bow, n—a type of bow that imposes a
adjustable within specified limits.
secondary system of control of the force-draw characteristic on
3.2.8 holding force, n—the force required to retain the
the usual limb geometry control system of the conventional
bowstring of a drawn bow at a specificATAactual draw length.
bow. This secondary control system can be composed of cams,
levers, cables, or other elements, or a combination thereof. The 3.2.9 let-down curve, n—the curve obtained when the force
dualcontrolsystempermitsgreatversatilityinthedesignofthe
necessary to restrain the bow from returning to brace height is
plotted versus the ATA actual draw length.
3.2.10 let-down force, n—the force required to retain the
1
This test method is under the jurisdiction of ASTM Committee F08 on Sports
Equipment and Facilitiesand is the direct responsibility of Subcommittee F08.16 on bowstring of the drawn bow at a specific ATA actual draw
Archery Products.
length during the let-down cycle. This let-down force differs
Current edition approved Nov. 1, 2009. Published December 2009. Originally
from the draw force at the same length by the amount of static
approved in 1998. Last previous edition approved in 2004 as F1880 – 98 (2004).
hysteresis.
DOI: 10.1520/F1880-09.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.2.11 let-off, n—that characteristic of an archery bow that
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
results in a reduction in the force necessary to increase the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. draw length of the bow after the highest level of draw force has
Copyright © ASTM International, 100 Barr Harbor Drive,
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
An American National Standard
Designation:F1880–98 (Reapproved 2004) Designation:F1880–09
Standard Test Method for the
1
Determination of Percent of Let-Off for Archery Bows
This standard is issued under the fixed designation F1880; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the procedure to be used to determine the percent of let-off for archery bows.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2
2.1 ASTM Standards:
F1832 Test Method for Determining the Force-Draw and Let-Down Curves for Archery Bows
3. Terminology
3.1Definitions:
3.1 Acronyms:
3.1.1 ATA—an acronym for the Archery Trade Association.
3.1.2ATA draw length—Archery Trade Association
3.2 Definitions:
3.2.1 ATA actual draw length, n—the perpendicular distance from the point where the shooting string of the bow contacts the
bottom of the nock slot of the arrow to a line parallel to the string at brace height through the pivot or low point of the hand grip
3
(draw length-pivot point), plus a standard dimension of 1 ⁄4 in. (44.5 mm). Draw length shall be measured with the arrow in the
full-draw position.
3.1.3—distance from the bow’s string at the nocking point location, while at the bow’s full draw condition, measured
3 1
perpendicular to a vertical line through the pivot point of the bow grip, plus 1 ⁄4 in. (+ ⁄4 , – 0 in.).
3.2.2 brace height, n—the distance in inches or millimetres from the shooting string of a bow to the pivot or low point of the
hand grip, measured perpendicular to the string at the un-drawn condition.
3.1.43.2.3 compound bow, n—a type of bow that imposes a secondary system of control of the force-draw characteristic on the
usual limb geometry control system of the conventional bow. This secondary control system can be composed of cams, levers,
cables,orotherelements,oracombinationthereof.Thedualcontrolsystempermitsgreatversatilityinthedesignoftheforce-draw
characteristic and simplifies the inclusion of let-off. In general, it is normal for compound bows to have greater stored energy than
conventional bows for a given level of peak or maximum draw weight.
3.1.5conventional bow, n—a bow constructed in the conventional manner, having two flexing limbs extending outwardly in
opposite directions from a handle.Asingle shooting string of a length shorter than the bow, connects the extreme ends of the limbs
causing them to assume a prestressed flexed condition. Drawing the bow causes additional bending and stressing of the limbs,
storing the energy necessary to propel the arrow. Control of the force-draw characteristic of the bow is exercised entirely by the
static and dynamic geometry of the flexing limbs.
3.1.6
3.2.4 draw, n—to move the shooting string of a bow from the rest or brace position toward the fully drawn position by applying
force to said string. Such action causes the limbs of the bow to bend and store energy. Moving the string from brace height to the
full-draw position corresponds to the draw cycle of a bow.
1
ThistestmethodisunderthejurisdictionofASTMCommitteeF08onSportsEquipmentandFacilitiesandisthedirectresponsibilityofSubcommitteeF08.16onArchery
Products.
´1
Current edition approved May 1, 2004. Published May 2004. Originally approved in 1998. Last pervious edition approved in 1998 as F1880-98 . DOI:
10.1520/F1880-98R04.
Current edition approved Nov. 1, 2009. Published December 2009. Originally approved in 1998. Last previous edition approved in 2004 as F1880 – 98 (2004). DOI:
10.1520/F1880-09.
2
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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F1880–09
3.1.7
3.2.5 draw force, n—that level of force necessary and coincidental with drawing a bow to a specific position within
...