3。A  method  or  providing  a  continuous   circuinferen- tial yoove  having  alternate  helical  and  parallel  section3 on a drum core, and consisting of providing  a  substan- tim*1y smooth surfac• for the outer periphery of the drum core, providing a  plurality  of  parallel  grooves  on  the out•。r periphery of a master  cylinder,  severinp•  the  mas- ter cylinder into 。a plurality of segm•。tits, interch:inying certain of the several segments, re-arranging tP。e severed segments   tend  lnterchanged   segments  on  the  smooth  out-

•-r p•<iiphery of th<• dr'am core whereby the grooves on the interchanged segments and the remaining sepm' ier。ts adjacent thereto are in substantial  a1i;;nment,  and  se- curing=  the  re-arranged  s•-gmcnts  on  the  drum  core。

4。A m•iliod of pro-viéting a counterba1m= ced gi ooving system on a drtim core consisting or utilizing a master cylinder having parallel groo•finp•  on  the  outer  periph- ery thereof, s<•vering tire master cy11nd<•r to provid• a plurality of segments, inteichanging certain of the sev- ered se;;n。' •nts and s•-curing of the  int•rcl。' anged ship- ments anlt r•maining segments  on  the  drum  core  to  pro- vide   the   counterbalanced    grooving   system  thereon。

5。A method of providing a counterbalanced grooving system o:i :i drum core consisiing of utilizing a sleeve havin3 parallel groo•/ing on the outer periph<-ry thereof, s-•vering the master  cylinder  to provide  at least  one psir of complementary wedge-shaped segments, interchanging the wedge-shaped segm•nts, and s•curinp• the se-meted steeple and interchmnged wedge-shap<•d se¿;nients on the drum core to provide the counterbalanced grooving there- On。

6。。A in。•thod of providing :i counterbalanced grooving system on a drum core consisting of  providing  a plurality of  parallel   grooves   on  the  outer  pcriph»•ry   of   a  sleeve of a size complementary to  the  c*rum  core,  deleting  a portion of at 1•ast one groove on the sleeve, severfinp• the sleeve into a plurality of arcuate segments, interchan¿;jng certain of the severed arcuate segments and assemblying thereof with  the  remaining  segm•nis around  the  doim  core in accords。rice with the desired counterbalanced grooving system, and securing the assembled segments to the  drum core。

7。A method of providing a counterbalanced grooving system on a drum core consisting of providing  a pli  :il1ty of: parallel p•rooves on the outer periphery of a sleeve of a size complementary of the drum core, severing the grooved sleeve to provide a plurality of substantially scmicylindri- cal sections and at least one pair of complementary wedge- shaped segments, interchanp=inp• the wedge-sh=«ped seg- ments, assembling the semi-cylindrical sections and inter- changed wedge-shaped  segments  around the outer peripii-

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ery of the drum core to provide the desired counterbal- anced grooving system thereon, and securing the sections and segments to the drum coi’e。

8。A method of providing a counterbalanced grooving system on a drum core consisting of providing a p1uralii•y of parallel  grooves  on the  outer periphery  of  a sleeve of a size complementary to the drum core, severing the grooved sleeve to provide a plurality of substantially semi- cylindrical sections and at least one pair of complementary wedge-shaped segments, del•tin;; one groove from at least one sev•r•d section or segment, interchan¡;ing the wedge- shaped segments, assemblinp• the semi-cylindrical sections and interchanged wedge-shaped segments on the outer periphery of th• drum core to provid• the desired counter- balanced grooving system thereon, and securing the sec- tions and segments to the drum core。