Patent application title: Archery recurve bow limb
Colin William Robertson (Toronto, CA)
IPC8 Class: AF41B514FI
Class name: Element for archery projector bow handle or attachment thereto
Publication date: 2011-10-20
Patent application number: 20110253120
The making of carbon steel recurve bow limbs involves a number of
procedures. Strips of annealed or softer carbon steel 18 to 20 inches
long and 1.5 inches wide have a hole drilled at one end of each strip for
attaching the limb to the bow, and grooves made at the other end for
attaching the bowstring. After forming the limbs into the curvature shown
in FIGS. 1. and 3. they are heated in a furnace for 45 minutes at about
1550 degrees F. and then quenched (cooled quickly) in oil which makes the
steel hard and brittle. The hardened limbs are then reheated for two
hours at about 700 degrees F. depending on the steel percent carbon
content and then air cooled. This tempering makes the steel strong,
tough, and elastic; the finished limbs act as cantilever springs when
used on a bow. This is a new application of the art and science heat
treating to make the limbs of very effective sporting recurve style
1. An archery recurve bow limb made from hardened and tempered carbon
steel, where the percentage carbon content range of the steel is from
0.30% to 1.30%.
2. An archery recurve bow limb as defined in claim 1, where the thickness range of the carbon steel used is from 0.050 inches to 0.150 inches.
3. An Archery recurve bow limb as defined in claims 1 and 2, where the carbon steel is tempered to a range of Rockwell "C" scale hardness, from 35 to 55 (HRc 35 to HRc 55).
CROSS-REFERENCE TO RELATED APPLICATIONS
 Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPEMENT
 Not Applicable.
REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX
 Not Applicable.
BACKGROUND OF THE INVENTION
 This invention relates to the usage of heat treating of carbon steel to make new and improved archery recurve bow limbs. Present archery recurve bows have long limbs typically made from fibreglass and wood which put such bows at a disadvantage when being used, stored or transported. Fibreglass and wood recurve bow limbs have a limited range of elasticity, and moderate tensile strength due to the materials physical properties that are weaker than heat treated carbon steel. Recurve bows have two detachable or non detachable limbs connected at there ends by a bowstring that propels an archery arrow when drawn backwards. The term "recurve" is the common name of this archery bow type, and there is no other reference data available here with this new applied usage of carbon steel.
BRIEF SUMMARY OF THE INVENTION
 Heat treated carbon steel recurve bow limbs improves fibreglass and wood recurve limbs by having a greater range of elasticity, strength and toughness due to the higher tensile strength of heat treated carbon steel. These improvements enable carbon steel recurve limbs to be shorter in length and have a greater curvature as shown in FIGS. 1 and 3, and thus a greater range of movement due to the elasticity of the limbs as shown in FIGS. 4 and 5. The greater curvature and tensile strength of carbon steel recurve bow limbs replaces the need for longer, less curved limbs as in ones made from fibreglass and wood.
 Carbon steel recurve limbs are 18 to 20 inches in length, where fibreglass and wood recurve limbs are typically 26 inches and longer. The shorter, greater curved carbon steel recurve limbs would also reduce the overall length of such a bow to about 38 inches, compared to fibreglass and wood recurve bows at 48 to 62 inches or longer in length. When carbon steel limbs are attached to the main bow frame known as the "riser" with the bowstring on, the bow is more compact for storage, transporting, and for usage in situations where space is limited, such as hunting blinds, tree stands, and while carrying through thick forest.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
 In FIG. 1. a side perspective of a typical carbon steel recurve bow limb is shown.
 In FIG. 2. the table shows the draw weights and arrow speeds for varying limb thickness.
 In FIG. 3. the carbon steel recurve limb bow has no bowstring attached, showing a side view of the curvature of the limbs.
 In FIG. 4. the carbon steel recurve limb bow has a bowstring attached and is undrawn.
 In FIG. 5. the carbon steel recurve limb bow is shown with the bowstring drawn back and the limbs extended, showing the great range of limb movement.
DETAILED DESCRIPTION OF THE INVENTION
 This invention involves the usage of heat treating by quench hardening and tempering carbon steel at various percent carbon content, thickness, and hardness to make new and improved archery recurve bow limbs that are strong, tough, and elastic. The steel carbon percent content in claim 1, is also known as medium and high carbon Spring steel and Tool steel, and ranges from 0.30% to 1.30%. The steel carbon percent content, the steel guage or thickness, and the Rockwell hardness "C" scale number, all must be used in proper combination to make a useful and effective carbon steel recurve bow limb.
 The claims cover these requirements to make a wide range of recurve bow limbs that equate to archery draw weights from 30 to 60 pounds (see FIG. 2.), which covers most usage situations from target shooting to hunting game. The range of Rockwell hardness from HRc 35 to HRc 55 in claim 3, is the useful applied range of hardness for the carbon steel in claim 1, to cover the different situations that the steel limbs would be used for. The Rockwell hardness scale is recognized and accepted as a global standard for measuring metal hardness.
 The greater curved carbon steel recurve limbs (FIG. 1, 3) that have a more elastic movement range (FIG. 4, 5) than fibreglass and wood limbs, have great mechanical energy as shown in FIG. 2 with a carbon steel recurve limb bow speeds of over 200 feet per second are achievable at draw weights of 55 and 60 pounds. This is a big improvement as it reduces arrow trajectory and extends shooting distances. It is important to note that arrow speeds are variable according to arrow weight, draw length and weight.
 In the testing of the carbon steel limbs as covered in FIG. 2 the range of limb thicknesses from 0.085 inches to 0.115 inches, were all tested with a limb width of 1.50 inches. Similar test results could be achieved by varying the limb thickness and width. A thicker, narrower limb would have a similar draw weight in pounds, as a thinner, wider limb. The large number of limb thickness and width variable combinations that could result in an effective limb, are why a wider range of limb thickness is claimed in claim 2. The same large number of limb variations would be possible with limb thickness and hardness combinations. A thinner, harder limb would have a similar draw weight as a thicker, softer limb. This is why the wide range of Rockwell hardnesses are claimed in claim 3.
Patent applications in class Bow handle or attachment thereto
Patent applications in all subclasses Bow handle or attachment thereto