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CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation application of U.S. Ser. No. 09/021,607 filed Feb. 10, 1998, now U.S. Pat. No. 6,385,911, which is a further continuation of U.S. Ser. No. 08/575,143, filed Dec. 19, 1995, now U.S. Pat. No. 5,765,308. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention is directed toward window operators, and more particularly toward window operators wherein the operating mechanism is supported directly by the cover and the base. The present invention is also directed toward window operators having reduced air/water infiltration. 
     2. Background Art 
     Windows are commonly constructed having a frame and a sash. The sash is pivotally secured to the frame for motion between a closed position, wherein the sash fits substantially within the frame, and an open position, wherein the sash is rotated relative to the frame so that the sash is not substantially within the frame. 
     Window operators used to control the movement of the sash between the open and closed positions are well known in the art. A window operator typically has a mounting base with a flat planar bottom secured to a corresponding flat planar surface on a sill of the frame. The mounting base rotatably mounts a gear or gear train and an arm. The gear or gear train meshes with a worm on a worm shaft having either a manually operated handle or motorized controller attached thereto. The arm is operatively connected to the sash of the window whereby rotation of the worm shaft results in rotation of the gear or gear train and the arm for movement of the window between the open and closed positions. Examples of typical manually operated window operators can be found in U.S. Pat. Nos. 4,253,276, 4,266,371, 4,445,794 and 4,845,830. 
     As illustrated in greater detail in U.S. Pat. Nos. 4,445,794 and 4,845,830, window operators are typically manufactured with the worm mounted in an upwardly angled generally tubular housing integrally formed in the base. Through an aperture in the housing, the worm meshes with the gear or, alternatively, the gear train. The gear is operably associated with the arm such that rotation of the worm results in rotation of the gear and associated arm about a fixed pivot pin. 
     To secure the worm in place in the tubular housing, a retainer bearing is threaded into position at an open end of the housing. The threaded retainer bearing, as shown in U.S. Pat. No. 4,253,276, may be held in place by use of an additional structural element, such as a locking pin, wedged between the threads of the bearing and the housing. Use of the locking pin may be avoided through the use of a specially shaped retainer bearing and limited deformation of the housing, such as shown in U.S. Pat. No. 4,505,601. Yet another alternative locking arrangement is shown in U.S. Pat. No. 4,445,794, wherein the retainer bearing locks the worm in place by stripping the threads at the open end of the housing as the retainer bearing is advanced into the housing 
     To install the assembled operator to the window, the flat planar bottom surface of the operator is placed against the flat planar bottom surface of a window frame sill. A gasket may be placed around the rear of the operator and between the operator and the sill. The base is then secured against the sill through the use of fasteners, such as screws, disposed through apertures in the base. 
     The above window operators are hard to make, and are consequently expensive to make. Cores or paddles must be used to shape the tubular housing. 
     Moreover, additional manufacturing steps must be performed and additional costs must be incurred because a separate, threaded retainer bearing is required to hold the worm in the tubular housing. Use of a separate retainer bearing increases the part count and the complexity of the assembly process. Furthermore, because a threaded retainer bearing is commonly used, additional preparatory machining steps must be performed on the tubular housing prior to assembly. Costs may be increased even further if an advanced locking mechanism, such as that shown in U.S. Pat. No. 4,505,601, is used because of the sophistication of the retainer bearing used and the assembly steps required. 
     Additionally, by securing the arm to the base using a simple pin, the operator is sensitive to variations in the tolerance of the constituent pieces and in the manufacturing processes. Therefore, in order to control the sensitivity of the device, as expressed in the gear arm backlash, tolerances and processes must be kept within narrowly defined limits. By restricting the range of allowable tolerances and processes, however, the cost per operator is necessarily increased. 
     Furthermore, the design of the above operators allows for air and water to infiltrate through the operator. Use of a retainer bearing normally prevents the operator from being assembled with a seal which acts to prevent substantial air flow through the worm housing opening. Additionally, air and/or water may infiltrate around the rear of the operator and between the bottom of the base and the flat planar surface of the window frame sill. 
     Attempts have been made in the industry to address some of these problems. For example, an operator has been designed which uses a conventional tubular worm housing, similar to that shown in U.S. Pat. No. 4,266,371, but in combination with an arm which is secured between mating interior surfaces of the cover and the base. In particular, a central post depends from an interior surface of the cover through an aperture in the base. The arm having a gear and a bearing associated therewith is pivotally mounted on the central post. The arm is secured in place by passing the central post through the aperture, and then riveting the post in place. 
     Additionally, this operator has a rearwardly protruding edge integral with the base disposed around the rearwardly facing surface of the base. A gasket may be placed around the rearwardly protruding edge to limit the infiltration of water and air around the operator. 
     However, this operator still presents all of the problems outlined above when a conventional worm housing integral with the base is used. Additionally, this operator fails to address the problem of infiltration of air and/or water at the base/sill interface. 
     The present invention is directed toward overcoming one or more of the problems discussed above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, an operator for controlling the movement of a window sash relative to a frame between open and closed positions includes a base attachable to the frame and having a first support surface, and a cover secured to the base and having a second support surface with a hole therethrough defining an internal shoulder, the second support surface mating with the first support surface. An arm is pivotally secured to the base and attachable to the sash to control the movement of the sash between open and closed positions. A worm drivably engages the arm. The worm has a worm shaft and a worm shoulder disposed on the worm shaft. The worm is directly supported by the first and second surfaces at one end and the worm shoulder engages the internal shoulder as the worm shaft protruding from the hole. 
     In another aspect of the invention, an operator for controlling the movement of a window sash relative to a frame between open and closed positions comprises a base attachable to the frame and having a first support surface and an aperture, and a cover secured to the base and having a second support surface with a hole therethrough defining an internal shoulder, the second support surface mating with the first support surface. A post extends from the cover and through the aperture. An arm is pivotally secured to the post and attachable to the sash to control the movement of the sash between open and closed positions. A worm drivably engages the arm and includes a worm shaft and a worm shoulder disposed on the worm shaft. The worm is directly supported by the first and second surfaces at one end and the worm shoulder engages the internal shoulder with the worm shaft protruding from the hole. 
     In an additional aspect of the invention, a method of manufacturing a window operator is provided wherein the operator includes a base attachable to a frame and having a first support surface and a plurality of apertures, a cover secured to the base and having a second support surface with a hole therethrough defining an internal shoulder, the second support surface mating with the first support surface, a central post and a plurality of fastener posts extending from the cover and through the plurality of apertures, an arm pivotally secured to the central post and attachable to a sash to control the movement of a sash between open and closed positions, and a worm drivably engaging said arm and having a worm shaft and a worm shoulder disposed on the worm shaft, said worm directly supported by the first and second surfaces at one end and the worm shoulder engaging the internal shoulder with the worm shaft protruding from the hole. The method includes the steps of passing the worm shaft through the hole with the worm shoulder engaging the internal shoulder and the worm disposed against the first support surface, fitting the arm to the central post, the arm in drivable engagement with the worm, placing the base and the cover together with the worm disposed between the first and second support surfaces and the central post and plurality of fastener posts protruding through the plurality of apertures, forming the central post, controlling the time and force applied in said central post forming step to eliminate the axial play along the central post, and securing said plurality of fastener posts. 
     In a further aspect of the invention, an operator for use with a window having a frame with a raised surface protruding from a frame sill and a sash moveable relative to the frame between open and closed positions includes a base having an interior support surface and a bottom exterior surface with a slot therein, the base attached to the frame with the raised surface fitting substantially within the slot. An arm is pivotally secured to the base and attachable to the sash to control the movement of the sash between open and closed positions. A worm is disposed within the interior support surface and drivably engages the arm. 
     In another aspect of the invention, an operator for use with a window having a frame with a raised surface protruding from a frame sill and a sash moveable relative to the frame between open and closed positions includes a base having a first support surface and a bottom exterior surface with a slot therein, the base attached to the frame with the raised surface fitting substantially within the slot, and a cover secured to the base and having a second support surface with a hole therethrough defining an internal shoulder, the second support surface mating with the first support surface. An arm is pivotally secured to the base and attachable to the sash to control the movement of the sash between open and closed positions. 
     A worm drivably engages the arm and has a worm shaft and a worm shoulder disposed on the worm shaft. The worm is directly supported by the first and second surfaces at one end and the worm shoulder engages the internal shoulder with the worm shaft protruding from the hole. 
     It is an object of the invention to provide a window operator using parts which are easier and less expensive to manufacture and assemble. 
     It is a further object of the invention to provide a window operator which is less sensitive to tolerance or assembly process variations. 
     It is also an object of the invention to provide a window operator which prevents substantial air and water infiltration therethrough. 
     It is additionally an object of the invention to provide a window operator system with a complete sealing surface at the system/window interface which prevents substantial air and water infiltration therethrough. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of an exemplary embodiment of the present invention; 
     FIG. 2 is a bottom plan view of a cover according to an exemplary embodiment of the present invention with a worm disposed in a support surface; 
     FIG. 3 is a plan view of a base of the present invention; 
     FIG. 4 is a bottom plan view of an assembled operator according to the present invention with the arm partially shown; 
     FIG. 5 is a cross-sectional view taken along line  5 — 5  in FIG. 4; 
     FIG. 6 is a perspective view of an exemplary embodiment of the present invention installed to a window having a frame and a sash; 
     FIG. 7 is cross-sectional view of a window showing an exemplary embodiment of the present invention installed therein with the arm and part of the handle removed; 
     FIG. 8 is a plan view of an exemplary embodiment of a window operator gasket fitting tool for use with an exemplary embodiment of the present invention; 
     FIG. 9 is a side view of the window operator gasket fitting tool; 
     FIG. 10 is a cross-sectional view of the window operator gasket fitting tool taken along line  10 — 10  in FIG. 9; 
     FIG. 11 is cross-sectional view of a window and a window operator gasket fitting tool showing the window operator gasket fitting tool in an intermediate position relative to an opening in a sill of the window; and 
     FIG. 12 is a partial elevation view showing a gasket fitted around an opening in a window sill. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An exemplary embodiment of the present invention is shown generally at  10  in FIG. 1. A cover  12  is attached to a base  14 . Disposed between mating surfaces of the cover  12  and the base  14  is a worm  16  having a worm shaft  18  extending through an aperture  20  in the cover  12 . An arm  22  is also pivotally secured between the cover  12  and the base  14 . The arm  22  is drivably engaged by the worm  16  at one end and is capable of being secured to a rail  24  of a sash  26  at the other (see FIG.  6 ). 
     More specifically, referring to FIGS. 1,  2  and  5 , the cover  12 , preferably of a zinc die cast manufacture, has a central tapered cylindrical post  28  and four tapered cylindrical fastener posts  30  protruding outwardly from an interior side of the cover  12 . The fastener posts  30  are spaced to roughly coincide with the four corners of the cover  12 . 
     The cover  12  also has an angled tubular surface  32 . At one end of the tubular surface  32  is the aperture  20 . The aperture  20  is formed as the intersection of a circular cylinder and an elliptical cylinder. A wall transverse to the axis of the tubular surface  32  surrounds the aperture  20  and defines an internal shoulder  34  (see FIG.  5 ). At the second end of the tubular surface  32  is an outwardly protruding stop  36 . The stop  36  has a partially cylindrical surface  38  preferably co-axial with the axis of tubular surface  32  and capable of contacting a first end of the worm  16  (See FIG.  5 ). 
     The worm  16  is disposed within the tubular surface  32  such that the worm shaft  18  protrudes from the aperture  20 . A frustoconical section intermediate to the ends of the worm shaft  18  and having a surface transverse, and preferably perpendicular, to the axis of the worm shaft  18  defines a worm shaft shoulder  40 . When the worm shaft  18  is placed through the aperture  20 , the worm shaft shoulder  40  and the internal shoulder  34  cooperate to prevent the outward axial motion of the worm  16 . 
     Preferably, a bushing  42  is placed between the shaft shoulder  40  and the internal shoulder  34 . The bushing  42  substantially prevents the movement of air and water along the worm shaft  18  and through the aperture  20  in the cover  12 . The bushing  42  is preferably made of a resilient material, such as plastic. 
     The arm  22  is rotatably mounted to the central post  28 , with the central post  28  extending through a circular aperture  44  in the arm  22 . Preferably, a tubular bearing  46  is disposed between the cover  12  and the arm  22  along the central post  28 . Most preferably, the bearing  46  is placed in an interference fit with the cover  12 , centering on a raised surface  47  protruding from the cover  12 . 
     Preferably, the arm  22  has a first elongated end which is attachable to the sash  26  and a partially circular second end  48  in which is formed an integral worm gear  50 . The worm gear  50  meshes with the worm  16 , whereby rotation of the worm  16  causes the arm  22  to rotatably pivot about the central post  28 . Alternatively, a separate worm gear may be disposed on the central post  28  and secured to the arm  22  such that rotation of the worm  16 , in mesh with the separate worm gear, causes the arm  22  to pivot about the central post  28 . 
     The base  14 , also preferably of die cast zinc manufacture, has a central circular aperture  52  and four circular fastener post apertures  54  (see FIGS. 3,  4 , and  5 ). The central aperture  52  and the fastener post apertures  54  correspond spatially with the central post  28  and the fastener posts  30 , respectively. 
     The base  14  has an angled tubular worm support surface  56  and a depressed trapezoidally-shaped stop support surface  58 . The worm support surface  56  mates with the tubular surface  32  and the stop surface  38  to define an enclosure  60  therebetween in which the worm  16  is disposed. Together, the worm support surface  56 , the internal shoulder  34 , the worm shoulder  40 , the tubular support surface  32  and the stop surface  38  substantially prevent the axial and transverse motion of the worm  16 . 
     The stop support surface  58  defines a depression in which the stop  36  is seated. The stop support surface  58  substantially prevents the movement of the stop  36  along the interior surface of the base  14  when the base  14  is secured to the cover  12 . 
     On the bottom side of the base  14  is formed a slot  62  of rectangular cross-section which extends from one side of the base  14  to the other. As shown in FIG. 7, a raised wall  64  of rectangular cross-section extending along a sill  66  of a frame  68  fits substantially within the slot  62  when the operator  10  is secured to the frame  68 . The wall  64  prevents the unobstructed flow of air and water along the bottom of the base  14  between the base  14  and the sill  66 . 
     Additionally, a gasket  70  may be placed around an opening in the sill  66  to ensure that a sealing surface is provided around the operator  10 . When the operator  10  is secured to the sill  66 , the gasket  70  fits around a rearwardly facing edge  72  protruding from a rearwardly facing surface of the cover  12  and the base  14 . The gasket  70  ensures that a water and airtight sealing condition is maintained between the operator  10  and the sill  66 . 
     To ensure proper placement of the gasket  70 , a special window operator gasket fitting tool is used, shown generally as  74  in FIGS. 8-11. The tool  74  includes a support surface  76 , a handle  78 , and a raised central portion  80 . The support surface  76  has a raised outer edge  82 , defining a groove  84  between the outer edge  82  and the central portion  80 . 
     During installation, the gasket  70 , preferably made of polyethylene foam with an adhesive backing, is placed on the fitting tool  74  so that the gasket  70  seats within the groove  84  (see FIG.  11 ). The fitting tool  74  is then placed within the opening in the sill  66 . In doing so, the gasket  70  will be placed in the proper position for use with the operator  10  (see FIG.  12 ). Use of the tool  74  eliminates the need to apply the gasket  74  directly to the operator  10 , which might cause some alignment difficulties. 
     Preferably, the operator is assembled as follows. The bushing  42  is placed on the worm shaft  18 . The worm  16 , thus assembled, is disposed within the tubular surface  32  with the worm shaft  18  extending through the aperture  20  and the first end of the worm  16  seated on the stop surface  38 . The bearing  46  is then placed on the central post  28 , followed by the arm  22 . The arm  22  is positioned with the end  48  meshing with the worm  16  so that the arm  22  will lie parallel to the rear of the operator  10  in a first position, and perpendicular to the rear of the operator  10  in a second position when the worm  16  rotated. Finally, the base  14  is positioned with the central post  28  and fastener posts  30  protruding through the central aperture  52  and the fastener post apertures  54 . 
     The posts  28 ,  30  are then formed and staked to fasten the cover  12  to the base  14 . To eliminate warpage of the parts in the operator  10 , the central post  28  is secured first using a radial forming method. In performing this radial forming method, a radial riveter is preferably used, having a forming tool designed to create a flat surface on the center post  28 . Through control of the time and force parameters, the axial play in the assembled arm  22  can be greatly reduced, preferably to less than a 0.005 inch gap between components. 
     The specific settings for the time and force parameters will need to be adjusted depending on the characteristics of the cover  12 , the base  14 , the center post  28 , the arm  22  and the associated bearing  46 . For example, the parameters will necessarily vary with the arm thickness and the amount of interference between the bearing  46  and the surface of the base  14  designed to receive the bearing  46 . However, it has been found that preferably the time required to perform the radial forming method varies between 1 and 2.5 seconds, and that the force behind the forming tool varies between 1200 and 2400 pounds. 
     After the central post  28  is formed, the fastener posts  30  are preferably staked simultaneously, although alternatively the posts may be staked in a number of different sequences, including individually, for example. In particular, during the staking process, the operator  10  is held stationary while four flat-faced punches are used to simultaneously impart a significant force to the four fastener posts  30 . The force imparted to the fastener posts  30  causes the post material to extrude outwardly, thereby securely fasting the corners of the cover  12  to the base  14 . 
     This operator  10  has a number of advantages. The use of mating surfaces on the cover  12  and the base  14  to support the worm  16  and the arm  22  allows for the straight die cast manufacture of the cover  12  and the base  14  without use of paddles and cores. Additionally, by using mating surfaces on the cover  12  and the base  14  to directly support the worm  16 , the number of pieces required for assembly of the operator  10  can be reduced. Moreover, the use of mating surfaces on the cover  12  and the base  14  to secure the arm  22  allows for greater range of tolerances and processes to be used to manufacture the arm  22  and associated gear. 
     Additionally, the elimination of the retainer bearing allows for the placement of the bushing  42 , substantially limiting the flow of air and water through the enclosure  60 , along the worm shaft  18  and out of the operator  10 . Moreover, the slot  62  and corresponding raised wall  64  on the sill  66  cooperate to prevent air and water infiltration along the operator/sill interface in a highly effective fashion. 
     Furthermore, by spinning down the central post  28  first, and then staking down the fastener posts  30 , warpage of the parts and loss of fit will be reduced or eliminated. 
     Still other aspects, objects and advantages of the present invention can be obtained from a study of the specification, the drawings and the appended claims.

Summary:
An operator for controlling the movement of a window sash relative to a frame with a raised surface along a frame sill thereof, wherein the operator includes a base having a first support surface, an aperture and a bottom exterior surface with a slot therein, the base attached to the frame with the raised surface fitting substantially within the slot. Also a method for manufacturing the operator includes the steps of passing the worm shaft through the hole with the worm shoulder engaging the internal shoulder and the worm disposed against the first support surface, fitting the arm to the central post, the arm in drivable engagement with the worm, placing the base and the cover together with the worm disposed between the first and second support surfaces and the central post.