ASTM F1880-98
(Test Method)Standard Test Method for the Determination of Percent of Let-Off for Archery Bows
Standard Test Method for the Determination of Percent of Let-Off for Archery Bows
SCOPE
1.1 This test method establishes 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.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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An American National Standard
Designation: F 1880 – 98
Standard Test Method for the
Determination of Percent of Let-Off for Archery Bows
This standard is issued under the fixed designation F 1880; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.5 conventional bow, n—a bow constructed in the con-
ventional manner, having two flexing limbs extending out-
1.1 This test method establishes the procedure to be used to
wardly in opposite directions from a handle. A single shooting
determine the percent of let-off for archery bows.
string of a length shorter than the bow, connects the extreme
1.2 This standard does not purport to address all of the
ends of the limbs causing them to assume a prestressed flexed
safety concerns, if any, associated with its use. It is the
condition. Drawing the bow causes additional bending and
responsibility of the user of this standard to establish appro-
stressing of the limbs, storing the energy necessary to propel
priate safety and health practices and determine the applica-
the arrow. Control of the force-draw characteristic of the bow
bility of regulatory limitations prior to use.
is exercised entirely by the static and dynamic geometry of the
2. Referenced Documents
flexing limbs.
3.1.6 draw, n—to move the shooting string of a bow from
2.1 ASTM Standards:
the rest or brace position toward the fully drawn position by
F 1832 Method for Determining the Force-Draw and Let-
applying force to said string. Such action causes the limbs of
Down Curves for Archery Bows
the bow to bend and store energy. Moving the string from brace
3. Terminology
height to the full-draw position corresponds to the draw cycle
of a bow.
3.1 Definitions:
3.1.7 draw force, n—that level of force necessary and
3.1.1 AMO—an acronym for the Archery Manufacturers
coincidental with drawing a bow to a specific position within
and Merchants Organization.
its draw length.
3.1.2 AMO draw length, n—the perpendicular distance from
3.1.8 force-draw curve, n—the curve obtained when the
the point where the shooting string of the bow contacts the
draw force is plotted versus the draw length for a given bow.
bottom of the nock slot of the arrow, to a line parallel to the
3.1.9 full draw, n—the position in a draw cycle of a bow
string at brace height through the pivot or low point of the hand
from which the string of the bow is released and the force
grip (draw length-pivot point), plus a standard dimension of 1
3 applied to the rear of the arrow to commence the launch. The
⁄4 in. (44.5 mm). Draw length shall be measured with the
full-draw position of individual archers will vary due to
arrow in the full draw position.
personal physical characteristics and shooting style. Archery
3.1.3 brace height, n—the distance in inches or millimeters
bows are specified as to the range of draw length that they will
from the shooting string of a bow to the pivot or low point of
accommodate to permit archers to select a size that will fit
the hand grip, measured perpendicular to the string.
them. Precise draw length is less of a factor on conventional
3.1.4 compound bow, n—a type of bow that imposes a
bows as compared to compound bows since it is ideal to match
secondary system of control of the force-draw characteristic on
the draw length of the archer to the position of maximum
the usual limb geometry control system of the conventional
let-off in the draw cycle of the compound bow. The position of
bow. This secondary control system can be composed of cams,
maximum let-off for compound bows usually is adjustable
levers, cables, or other elements, and combination thereof. The
within specified limits.
dual control system permits great versatility in the design of the
3.1.10 holding force, n—the force required to retain the
force-draw characteristic and simplifies the inclusion of let-off.
bowstring of a drawn bow at a specific draw length.
In general, it is normal for compound bows to have greater
3.1.11 let-down curve, n—the curve obtained when the
stored energy than conventional bows for a given level of peak
force necessary to restrain the bow from returning to brace
or maximum draw weight.
height is plotted versus the draw length.
3.1.12 let-down force, n—the force required to retain the
bowstring of the drawn bow at a specific draw length during
This test method is under the jurisdiction of ASTM Committee F-8 on Sports
the let-down cycle. This force differs from the draw force at the
Equipment and Facilities and is the direct responsibility of Subcommittee F08.16 on
Archery Products. same length by the amount of static hysteresis.
Current edition approved April 10, 1998. Published September 1998.
3.1.13 let-off, n—that characteristic of an archery bow that
Annual Book of ASTM Standards, Vol 15.07.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 1880
results in a reduction in the force necessary to increase the let-down for this calculation. This test method defines the two
draw length of the bow after the highest level of draw force has methods and distinguishes between them.
been reached. This is a characteristic generally associated with
5. Determination of the AMO Percent of Let-Off
but not restricted to, compound type bows.
5.1 Use of the Force-Draw Curve—The values of peak
3.1.14 let-off force, n—the minimum force required to retain
force and let-off force used to calculate the AMO percent of
the bowstring of the drawn bow subsequent to peak draw force
let-off shall be tak
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