referring now to fig1 a rotary patio door lock 10 , according to the present invention , is mounted on a sliding patio door assembly 12 which consists of an inner door 14 and an outer door 16 . typically , one of the doors 14 , 16 is fixed and the other of the doors 14 , 16 slides . the door 14 has a frame 18 to which the lock 10 is mounted by three mounting screws 20 . the lock 10 has a first body shell member 22 and a second body shell member 24 which are fixed to one another to form a case 25 by expanding a small diameter end - extension 54 of a shaft 26 , so as to enclose a barrel lock assembly 28 , disk 64 and bolt 30 ( see fig2 ). a locking bolt 30 extends out of the lock 10 on both sides thereof . the door 16 has a plurality of apertures 32 drilled therein into which the bolt 30 may be extended so as to lock the sliding door assembly 12 in the desired position , which may be either completely closed or partially opened to provide ventilation if desired . fig2 is an exploded view of the rotary lock 10 showing the first and second body shell members 22 , 24 separated from one another . the barrel lock assembly 28 is seen to have a barrel lock 34 which is disposed in a barrel lock housing 36 and is locked into the housing 36 by a spring - biased retainer leaf 90 . the locking cam lug 38 has an aperture 40 formed thereon into which a cam 42 depending from the barrel lock 34 is disposed . a key 44 is used to rotate the barrel lock 34 within the housing 36 so as to selectively extend or retract the locking cam lug 38 into or out of retaining slots 46 , 48 of shell 22 and 46a and 48a of shell 24 when assembled as showin in fig1 to form the case 25 . the body shell members 22 , 24 each have three mounting apertures 50 formed therein to receive the three mounting screws 20 which extend through the case 25 to mount the lock 10 to the door frame . the shaft 26 has a shoulder 52 and a smaller diameter tip 54 . the first body shell member 22 has a face 56 , with a passage 58 formed therein to receive the tip 54 of the shaft 26 , so that the shaft shoulder 52 abuts the face 56 . the second body shell member 24 has an alignment pin 60 which mates with a cylindrical recess 62 in the first body shell member 22 so as to properly align the body shell members 22 , 24 when they are placed together . after being positioned together , the tip 54 is expanded against a shoulder ( not shown , see fig3 ) in the passage 58 to thereby hold the body shell members 22 , 24 together to form the unitary case 25 which can not be separated into the shell members 22 , 24 without drilling out the expanded tip 54 . a disk 64 is mounted on the shaft 26 so as to be rotatable thereabout . the disk 64 has an arcuate pinion gear section 66 formed thereon so as to be offset approximately 90 degrees from a crank pin 68 extending outwardly from the disk 64 parallel to a bearing aperture 70 , through which the shaft 26 extends so as to rotatably mount the disk 64 on the shaft 26 . the bolt 30 has a rack portion 72 formed thereon of circular teeth in the central portion thereof , the bolt 30 being selected to be of a length so as to extend out both sides of the lock 10 . as seen in fig2 the bolt 30 is disposed within pairs of semi - circular recesses 74 , 76 formed in the first body shell member 22 and complementary recesses 74a , 76a formed in the second body shell member 24 . referring now to fig3 the rotary patio door lock 10 is shown in left side elevational view , partially broken away , so as to illustrate the attachment of the two body shell members 22 , 24 together . the shaft 26 is seen to abut the face 56 and the tip 54 to extend through the passage 58 which opens onto a face -- 78 of the first body shell member 22 so as to form an enlarged aperture 80 . the end of tip 54 has been expanded , shown by 54a , into the enlarged aperture 80 , thereby locking the two body shell members 22 , 24 together to form the case 25 . as shown in fig3 the barrel lock assembly 28 is in its extended position , in which it extends the greatest length beyond the body shell members 22 , 24 . the barrel lock assembly may be fixed in this disposition by rotating the lock 34 by the key 44 , so as to cause the locking cam lug 38 to extend into the first retaining slots -- 46 , 46a . referring now to fig4 there is shown a plan view , partially broken away , of the lock 10 . in fig4 the lock 10 is locked in its extended barrel lock assembly disposition , thereby locking the bolt 30 in a disposition so as to extend principally out of the right hand side of the lock 10 . the bolt 30 is held in this locked disposition by the engagement of the rack portion 72 with the arcuate pinion gear portion 66 of the disk 64 , which is fixed against rotation by the combined engagement of the crank pin 68 with an elongated lateral recess 82 formed in a laterally offset extension arm 84 of the barrel housing 36 ( see fig7 ). as will be apparent from fig3 and 4 , the extension arm 84 is laterally offset with respect to the plane of disk 64 , the plane of the disk 64 being coplanar with the bolt 30 . in fig6 the lock 10 is shown in its barrel lock assembly retracted disposition . the disk 64 has been rotated clockwise from the disposition shown in fig4 thereby causing the pinion gear portion 66 , which engages the rack portion 72 of the bolt 30 , to move the bolt 30 to the left , thereby causing the bolt 30 to extend principally out of the left hand side of the lock 10 . the clockwise rotation of the disk 64 is caused by forward movement of the barrel housing 36 into the lock case 25 which rotates the crank pin 68 disposed in the elongated lateral recess 82 of the extension arm 84 . in fig6 the barrel lock assembly 28 is shown as unlocked in the retracted position , as the locking cam lug 38 does not extend into the second retaining slot 48a . rotation of the key 44 in a counter - clockwise direction will cause the locking cam lug 38 to be extended out into the slot 48a . in order to initiate the movement of the barrel lock assembly 28 from the disposition shown in fig4 to the disposition shown in fig6 the key 44 is inserted into the lock and rotated , thereby retracting the locking cam lug 38 into the barrel housing 36 , so as to permit the movement of the barrel lock assembly 28 in response to manual pressure by the user . fig7 is an isometric view of the barrel lock housing 36 which illustrates a slot 86 in which the locking cam lug 38 is disposed ( see fig2 ) so as to be selectively extendable therefrom and retractable therewithin . fig7 also illustrates the depending extension arm 84 and elongated lateral recess 82 which , in cooperation with the crank pin 68 , translates the linear longitudinal movement of the barrel lock assembly 28 into linear longitudinal movement of the bolt 30 in a direction normal to the barrel lock assembly movement by means of the bolt rack 72 and arcuate pinion gear 66 of the disk 64 . as will be seen in fig3 the axis of symmetry of the barrel lock assembly 28 lies in the plane of rotation of the arcuate pinion gear 66 , but the extension arm 84 is laterally offset therefrom . the arcuate pinion gear 66 and bolt 30 are coplanar with respect to one another , so that the longitudional axis of movement of the barrel lock assembly 28 intersects the longitudional axis of movement of the bolt 30 and is normal thereto . a particular advantage of the rotary patio door lock of the present invention is that the door lock 10 is either a right hand or a left hand lock . that is , the bolt 30 can be locked in an extended position either extending from the right hand side of the lock 10 or the left hand side of the lock 10 as desired . thus , the lock 10 can be mounted in either the lower portion of the door , and the key 44 inserted downwardly into the lock 10 , or the lock 10 can be mounted &# 34 ; upside - down &# 34 ; in the upper portion of the door , and the key 44 inserted upwardly into the lock 10 . in either such mounting , the body shell member 22 , through which the expanded tip end 54a is exposed , is placed against the door frame so as to cover the tip 54 . in such usage , the screws 20 have unidirectional heads , which prevent unscrewing the screws , so as to remove the lock 10 from the door 12 at the installation . conventional locks of this type , such as the lock shown in u . s . pat . no . 4 , 163 , 375 , are not designed for such use . a further advantage of the lock 10 with respect to conventional locks is that the barrel lock 34 may be removed from the lock 10 and a new barrel lock substituted therefor . such a feature is of particular advantage when it is desired to install a plurality of locks 10 in a residence , for example , without the necessity of the user having multiple different keys in order to operate the various locks . in order to provide for such a feature , the barrel lock 34 has a spring biased retainer leaf 90 ( see fig2 ) which is normally biased outwardly to retain the barrel lock 34 in the housing 36 by engaging an inner circumferential groove formed in the housing 36 and which opens into the slot 86 , so that both the retainer leaf 90 and locking cam 38 ( when retracted ) may rotate within the housing 36 upon rotation of the barrel lock 34 . the housing 36 has a small passageway 92 ( fig6 ) extending therethrough so as to open onto the retainer leaf 90 when the barrel lock 34 is in its unlocked position . the lock case 25 has a pair of holes 94 , 96 formed at the junction of the shells 22 , 24 so as to be in alignment with the passageway 92 when the barrel lock 34 is either unlocked or extended . when the lock 34 is in its extended position as shown in fig4 the passageway 92 in the housing 36 is aligned with the case hole 96 . when the lock assembly 28 is in the retracted position as shown in fig6 the case hole 94 is in alignment with the passageway 92 . in either such alignment , a small rod 98 may be inserted through the respective one of the case holes 94 , 96 and the passageway 92 so as to depress the retainer leaf 90 into the barrel lock 34 when and only when the barrel lock 34 is in its unlocked position with cam lug 38 retracted in the barrel lock housing 36 , thereby permitting the lock 34 to be withdrawn from the housing 36 by pulling on the key 44 . identically keyed new barrel locks 34 may then be inserted into the desired number of locks 10 , so as to provide the identically keyed feature for the user without the necessity of taking the lock 10 apart , which would destroy the lock 10 in view of the expanded end of the tip 54a which holds the two shell members 22 , 24 of the case 25 together .