yl ind rical ▁( plan et ary ) ▁sh ar pen ers ▁▁ ▁These ▁mechan isms ▁are ▁also ▁called ▁planet ary ▁sh ar pen ers , ▁in ▁reference ▁to ▁their ▁use ▁of ▁planet ary ▁g ears . ▁A ▁larger , ▁station ary ▁planet ary ▁sharp ener ▁can ▁be ▁mounted ▁on ▁a ▁des k ▁or ▁wall ▁and ▁power ed ▁by ▁a ▁hand ▁c rank . ▁Typ ically , ▁the ▁p enc il ▁is ▁inserted ▁into ▁the ▁sharp ener ▁with ▁one ▁hand , ▁and ▁the ▁c rank ▁is ▁turned ▁with ▁the ▁other . ▁This ▁rot ates ▁a ▁set ▁of ▁hel ical ▁cyl ind rical ▁cut ters ▁in ▁the ▁mechanism , ▁set ▁at ▁an ▁ac ute ▁angle ▁to ▁each ▁other . ▁The ▁multiple ▁cutting ▁edges ▁quickly ▁sh ar pen ▁the ▁p enc il , ▁with ▁a ▁more ▁precise ▁finish ▁than ▁a ▁single - bla de ▁device . ▁Some ▁cyl ind rical ▁sh ar pen ers ▁have ▁only ▁one ▁hel ical ▁cut ter ▁cyl inder , ▁but ▁most ▁have ▁two ▁cyl ind ers ▁or ▁more . ▁▁ ▁Most ▁planet ary ▁sh ar pen ers ▁have ▁a ▁large ▁opening , ▁with ▁a ▁rot atable ▁guide ▁disk ▁in ▁front ▁of ▁it ▁that ▁has ▁multiple ▁holes ▁of ▁different ▁sizes , ▁to ▁accommod ate ▁p enc ils ▁of ▁many ▁different ▁diam eters . ▁Advanced ▁models ▁have ▁a ▁spring - dri ven ▁holder ▁for ▁the ▁p enc il , ▁so ▁that ▁the ▁p enc il ▁automatically ▁is ▁pushed ▁into ▁the ▁mechanism ▁while ▁being ▁sh ar pen ed . ▁Some ▁versions ▁also ▁offer