9。A method  of  providing  a continuous circumfer•ntial

;;roove having alternate helical and para11e1 sections on a          drum core and consisting  of providing  a plurality of   par- allel grooves on the outer periphery of a cylindrical steeve,

cutting at least one pair of complem•。ntary wedge-shaped segments from the grooved sleeve, intercfianging the wedge-shaked segments, arranging th• se /ered sleeve and interchanged wedg•-shap<•d segments around the outer periphery of the drum core whereby the groove-s on the interchanged segments are in substantial  alignment with the grooves of the adjacent s-•gments to provide the con- tinuous helical and parallel groove, and securing the sev- ered sleeve and wedg•--shaped segments to the chair。  core。

10。A method of providing a continuous circumferen- tial groove having alternate  helical  and  parallel sections on a drum  core  and  consisting  of  providing  a plurality of parallel groos-es on the outer periphery of a cylindrical sleeve, deleting at least a portion of one groove from the sleeve, cutting at least one pair of complementary wedge- shaped segments from the grooved sleeve, interchanging the wedge-shaped segments, arranging the severed sleeve and interchanged wedge-shaped segments around the outer periphery of tire drum core whereby tne grooves of the interchanged segments are in substantial  alignment with the grooves on the sleeve to provide the continuous helical

: nd parallel groove, and securm' g the severed sleeve and xv•dg•e-shaped segments to the drum core。

11。A method of providing a counterbalanced groo-ring syst•m on a drum core and consisting of providing a plu- rality of parallel grooves on  a  master  cylinder, severing the yooved master cylinder into a plurality of segments comprising a pair of substantially scm'i-cylindrical s-•ctions and two pairs of compleme:itary wedge-shaped segments, interchanging the coinpiementary wedge-shaped segments of each pair trer•»of assembling th。 e semi-cylindrical sec- tions and the pairs of interchan;;ed wedge-shap=»d seg- ments aroun‹1 the outer periphery of the drum cor•, and s•-curing the sections  and segments to the drum   Core。

12。A mc"tnod of providing a counterba。lanced grooving system on a d ° core and consisting of providing a plu- rality of parall•1 grooves on a  master  cylinder, severing the grooved master cylinder Tinto a plurality of segments comprising a pair of substantially semi-cylindrical sections red two pafi-s of compiementary wedge-shap<•d segments,

‹Deleting a groove from at least one of the severed seg- ments of the master cylinder, interchanging the comple- in。eniary wedge-shaped segments of each pair thereof, as- sembling the semi-cylindrical sections and pairs of ,nter- changed wedge-shaped  segments around the outer periph-

ery of th»•  drum  core in a manner  v。'hcreby  the grooves of the interchanged wedge-shaped segments and the adja- cent semi-cylindrical sections are in substantial alignment, ar。d  securing the  assembled  sections  and s•grnents to the

5   drum  core。

13。A m-•thod or providing a counterbalanced grooving system on a drum core which consists of providinq• a plu- rality of parallel grooves on the outer periphery of a cylin- drical sleeve, severing the grooved sleeve along a plurality of spaced longitudinally extending lines to provide a plu- rality of arcuat• sections, severing a portion of the arcuate sections along canted longitudinally extending lines to provide at least one pair of complementary wedge-shaped segm•»nis, interchan¿;ing the wedge-shaped segments, as- sembling the arcuaie sections and interchanged wedge- shaped s•gments around the outer periphery of the drum core in a manner to provide a continuous groove between Lh•。interchanged wedge-shaped segments and the adjacent arcuate  segments,  and securing  the  assembled sep•ments