1、Designation: F 1880 98 (Reapproved 2004)An American National StandardStandard Test Method for theDetermination of Percent of Let-Off for Archery Bows1This standard is issued under the fixed designation F 1880; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the procedure to be used todetermine the percent of le
3、t-off for archery bows.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior
4、 to use.2. Referenced Documents2.1 ASTM Standards:2F 1832 Test Method for Determining the Force-Draw andLet-Down Curves for Archery Bows3. Terminology3.1 Definitions:3.1.1 ATAan acronym for the Archery Trade Association.3.1.2 ATA draw length, nthe perpendicular distance fromthe point where the shoot
5、ing string of the bow contacts thebottom of the nock slot of the arrow to a line parallel to thestring at brace height through the pivot or low point of the handgrip (draw length-pivot point), plus a standard dimension of134 in. (44.5 mm). Draw length shall be measured with thearrow in the full-draw
6、 position.3.1.3 brace height, nthe distance in inches or millimetresfrom the shooting string of a bow to the pivot or low point ofthe hand grip, measured perpendicular to the string.3.1.4 compound bow, na type of bow that imposes asecondary system of control of the force-draw characteristic onthe us
7、ual limb geometry control system of the conventionalbow. This secondary control system can be composed of cams,levers, cables, or other elements, or a combination thereof. Thedual control system permits great versatility in the design of theforce-draw characteristic and simplifies the inclusion of l
8、et-off.In general, it is normal for compound bows to have greaterstored energy than conventional bows for a given level of peakor maximum draw weight.3.1.5 conventional bow, na bow constructed in the con-ventional manner, having two flexing limbs extending out-wardly in opposite directions from a ha
9、ndle. A single shootingstring of a length shorter than the bow, connects the extremeends of the limbs causing them to assume a prestressed flexedcondition. Drawing the bow causes additional bending andstressing of the limbs, storing the energy necessary to propelthe arrow. Control of the force-draw
10、characteristic of the bowis exercised entirely by the static and dynamic geometry of theflexing limbs.3.1.6 draw, nto move the shooting string of a bow fromthe rest or brace position toward the fully drawn position byapplying force to said string. Such action causes the limbs ofthe bow to bend and s
11、tore energy. Moving the string from braceheight to the full-draw position corresponds to the draw cycleof a bow.3.1.7 draw force, nthat level of force necessary andcoincidental with drawing a bow to a specific position withinits draw length.3.1.8 force-draw curve, nthe curve obtained when thedraw fo
12、rce is plotted versus the draw length for a given bow.3.1.9 full draw, nthe position in a draw cycle of a bowfrom which the string of the bow is released and the forceapplied to the rear of the arrow to commence the launch. Thefull-draw position of individual archers will vary due topersonal physica
13、l characteristics and shooting style. Archerybows are specified as to the range of draw length that they willaccommodate to permit archers to select a size that will fitthem. Precise draw length is less of a factor on conventionalbows as compared with compound bows, since it is ideal tomatch the dra
14、w length of the archer to the position ofmaximum let-off in the draw cycle of the compound bow. Theposition of maximum let-off for compound bows usually isadjustable within specified limits.3.1.10 holding force, nthe force required to retain thebowstring of a drawn bow at a specific draw length.1Thi
15、s test method is under the jurisdiction of ASTM Committee F08 on SportsEquipment and Facilities and is the direct responsibility of Subcommittee F08.16 onArchery Products.Current edition approved May 1, 2004. Published May 2004. Originallyapproved in 1998. Last pervious edition approved in 1998 as F
16、 1880 - 98e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor D
17、rive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.11 let-down curve, nthe curve obtained when theforce necessary to restrain the bow from returning to braceheight is plotted versus the draw length.3.1.12 let-down force, nthe force required to retain thebowstring of the drawn bow
18、 at a specific draw length duringthe let-down cycle. This force differs from the draw force at thesame length by the amount of static hysteresis.3.1.13 let-off, nthat characteristic of an archery bow thatresults in a reduction in the force necessary to increase thedraw length of the bow after the hi
19、ghest level of draw force hasbeen reached. This is a characteristic generally associated with,but not restricted to, compound type bows.3.1.14 let-off force, nthe minimum force required to retainthe bowstring of the drawn bow subsequent to peak draw forceunder a condition of constant tension on the
20、bowstring.3.1.15 peak or maximum draw force, nthe maximumforce required to retain the bowstring of the drawn bow at aspecific draw length under a condition of constant tension onthe bowstring. No relaxation of the drawing force is permittedwhen measuring this force, since this introduces static hyst
21、er-esis. The peak or maximum force for compound bows usuallyoccurs about half way through the draw cycle, while onconventional bows it normally occurs at the end of the drawcycle since there is no let-off.3.1.16 percent of let-off, nthe difference between the peakor maximum draw force reached during
22、 the draw cycle of abow and the lowest level of draw force reached subsequent tothat peak, expressed as a percentage of the peak force.3.1.17 power-stroke, nthe distance in inches or millime-tres from brace height to full draw.3.1.18 static hysteresis, nthe difference in pounds ornewtons, measured u
23、nder static conditions, between the drawforce and the let-down force for any given draw length.Integrated over the full power stroke of the bow, the statichysteresis is expressed as foot-pounds or joules of energy.3.1.19 stored energy, nthe energy required to draw a bowfrom brace height to full draw
24、, usually expressed in foot-pounds or joules.3.1.20 zero intercept, nthe point of zero intercept isdefined as the brace height plus 134 in. (44.5 mm). It is the zeroforce position on the force-draw curve.4. Significance and Use4.1 It is recognized that certain designs of the cams used inthe compound
25、ing systems of archery bows cause variation inthe percent of let-off with change in draw length, draw weight,or both. This is true particularly with the style of cam thatachieves draw length adjustment by effectively altering thelength of the shooting string by any of several methods. In thiscase, t
26、he mid-draw length and the maximum draw weightobtainable (but not to exceed the maximum rated weight of thebow) shall be used to determine the official percent of let-offfor the bow in question.4.2 Historically, two methods have been in use to establishthe percent of let-off for archery bows. The mo
27、st commonmethod uses the peak draw force and the minimum holdingforce read from the force-draw curve to calculate the percent oflet-off. The second method uses the peak draw force from theforce-draw curve and the minimum holding force from thelet-down for this calculation. This test method defines t
28、he twomethods and distinguishes between them.5. Determination of the ATA Percent of Let-Off5.1 Use of the Force-Draw CurveThe values of peakforce and let-off force used to calculate the ATA percent oflet-off shall be taken from the force-draw curve. The peak forceis the maximum force obtained during
29、 the draw cycle. Thelet-off force is the low force read at the rated draw length. In allcases, the force shall be read within 2 s under continual pullconditions, without relaxation to reach the draw length speci-fied. This technique eliminated the hysteresis effect, which candistort the reading. Ref
30、er to Test Method F 1832 for the methodto be used in determining the force-draw curve.5.2 Method of CalculationThe percent of let-off shall becalculated using the following formula:percent let2off 5 100 peak force let2off force! / peak force (1)5.3 HysteresisThe reduction due to hysteresis shall not
31、 beconsidered in the determination of the force value at eitherpeak or let-off condition when determining the ATA percent oflet-off.5.4 Rating ConditionsThe bow shall be rated for percentof let-off with the draw length set in mid-range and the peakdraw weight adjusted to the maximum rated value for
32、thatspecific draw length.6. Effective Percent of Let-Off6.1 Hysteresis EffectThe difference in force at the fulldraw condition between the draw and let-down curves isnormally in the range of 6 to 10 % of the peak draw force.Under certain conditions, this hysteresis can increase theeffective percent
33、of let-off, however, the exact effect is depen-dent on the specific bow design. The hysteresis becomes afactor when the bow is drawn past full draw and let down orrelaxed to the anchor position. It is not a factor when thebowstring is drawn to the anchor position without incipientlet-down. For this
34、reason, it can influence let-off, but its effectis dependent upon the technique used to bring the bowstring tothe anchor position.7. Precision and Bias7.1 PrecisionIt is not practical to specify the precision ofthe procedure in this test method because it has not yet beendetermined.7.2 BiasThe proce
35、dure described in this test method hasno bias because the percent of let-off is defined only in termsof this test method.8. Keywords8.1 brace height; draw length; force-draw curve; full-draw;let-offF 1880 98 (2004)2ASTM International takes no position respecting the validity of any patent rights ass
36、erted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time b
37、y the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will rece
38、ive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM Inte
39、rnational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).F 1880 98 (2004)3
