Abstract:
A CNC machine makes a single speed reducer by forming a worm recess, a worm gear recess, and a worm shaft groove that is discontinuous at the worm recess in a first solid block of aluminum. Matching recesses and grooves are formed in a second solid block of aluminum in the same way so that a worm cavity, a worm gear cavity, and a worm shaft bore are formed when the two blocks are placed in juxtaposition to one another. The worm shaft bore enables the reducer to have two different mounting configurations. A double speed reducer made by the same techniques has even more mounting configurations. The design also minimizes gear lash, end play, and inertia generated coasting and accommodates power transmission systems other than gear trains.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   This invention relates, generally, to speed reducers. More particularly, it relates to a method for making speed reducers from solid metallic blocks by CNC machining. 
   2. Description of the Prior Art 
   The conventional way to make a speed reducer is to cast the individual parts thereof in a mold. The parts that are individually cast include the housing and the gears or other power transmission means within the housing. The working parts of the speed reducer are assembled and the completed assembly is placed into the housing. 
   The housing is typically a box-like structure that encloses the gear train or other power transmission system. The housing not only protects the parts therewithin from the elements, it also acts as a safety cover to protect individuals from sprocket gears, sprocket chains, and the like that may form a part of the speed reducer. 
   Worms and worm gears are well-suited for use in speed reducers, but there are many other types of gears that can be used. For example, helical, bevel, mitre, and spur gears or any combination thereof can be used. 
   Nor are gears the only suitable means for performing lifting functions. For example, there are numerous hydraulic, pneumatic, and other power transmission systems that can be employed. However, in most applications a gear train is less expensive and usually more practical than such alternatives. 
   Speed reducers of the type that employ worms and worm gears have distinct advantages over other gear train power transmission systems. They have particular utility where a high-ratio speed reduction is required but where space is limited. They operate quieter and smoother than speed reducers employing sprocket gears and sprocket chains, helical gear trains, and the like. 
   Speed reducers that incorporate worms and worm gears also offer good resistance to back driving because a worm gear cannot drive its associated worm. When properly designed and installed for a particular application, they are generally self-locking when the load is at rest. For example, where a boat is lifted from water by a lift that incorporates a worm and worm gear speed reducer, the worm and worm gear speed reducer will self-lock and thus prevent the boat from re-entering the water. When a boat is being lowered, any tendency for lowering to continue after the motor has been turned off is called “inertia-generated coasting.” Worm and worm gear speed reducers are resistant to such inertia-generated coasting. 
   A worm and worm gear double speed reduction system is even more resistant to inertia-generating coasting, making such systems preferable to other gear systems when used for lifting and lowering heavy loads. 
   For example, spur gears exhibit little or no resistance to inertia-generated coasting and thus are not suitable for use in applications requiring the lifting of heavy objects where inertia-generated coasting is undesirable. 
   The success of a design is determined in large part by the gear material selected. For example, a system having steel worms and cast iron worm gears has only half the lifting capacity as a system having hardened steel worms and bronze worm gears. 
   The designer must also consider the amount of motion between the worm and the worm gear, also known as gear lash, and the lateral motion of the worm, also known as end play. 
   Moreover, appropriate thrust bearings and lubrication are critical to minimize unwanted friction to ensure efficient operation. 
   A weight-lifting and holding system is said to have a service factor of 1.0 if the system is subjected to a moderate shock lasting no more than fifteen (15) minutes for each two (2) hour period of uniform operation over a ten (10) hour or less day. A service factor of 1.0 or less is considered normal for the boatlift industry. It follows that a successful design should employ a worm and worm gear speed reducer having a hardened steel worm and a bronze worm gear, should minimize gear lash and end play, and should be installable in small spaces. Ideally, the design should enable the speed reducer to be re-configured as needed so that it can fit into differing areas having limited space. 
   An ideal design should also maintain the designed gear lash and end play with consistent repeatability, i.e., the gear lash and end play should remain about the same over many cycles of operation. 
   The known methods for making speed reducers, including the casting of individual parts as mentioned above, assembling the parts, and housing the assembled parts, is a relatively expensive process. If a new method could be found that substantially reduces the cost of manufacturing a speed reducer, it would revolutionize the industry. 
   However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the art of making a speed reducer could be advanced in a pioneering way. 
   SUMMARY OF INVENTION 
   The long-standing but heretofore unfulfilled need for an improved method for manufacturing a speed reducer is now met by a new, useful, and nonobvious invention. 
   In a first embodiment, a novel single speed reducer is manufactured from a first solid block of metallic construction and a second solid block of metallic construction having a common width, height, and thickness as the first solid block. 
   A first plurality of recesses is formed in the first solid block and a second plurality of mating recesses is formed in the second solid block by a CNC machine. When the first and second solid blocks are placed in confronting relation to one another, the union of the first and second pluralities of recesses forms a plurality of cavities that accommodate the various parts of a power transmission system. Thus, the first solid block and the second solid block form a speed reducer housing when disposed in confronting relation to one another. 
   The use of a CNC machine to form a plurality of mating recesses in a pair of metallic blocks to form a plurality of cavities adapted to accommodate the parts of a power transmission system is the primary teaching of the present invention. The recesses can be machined with precision so that the respective positions of the parts of the power transmission system can be precisely maintained against slippage, migration, and the like. For example, where a worm and worm gear power transmission is employed, gear lash and end play are tightly controlled. 
   Any type of power transmission system capable of lifting a heavy weight, of self-locking, and that is resistance to inertia-generated coasting may be positioned within the power transmission cavity and the novel method is not limited to power transmission systems of the type employing gear trains. 
   In a preferred embodiment, the power transmission system includes a worm and worm gear arrangement because of the low cost and practicality of such arrangements. However, the primary point of novelty of the present invention lies not in the use of worm and worm gear arrangements as the power transmission system, but in the use of a CNC machine to form first and second recesses in first and second metallic blocks, respectively, that collectively form a power transmission-receiving cavity when the first and second metallic blocks are placed into confronting relation to one another. 
   Where a worm and worm gear power transmission system is employed, the worm is mounted on a worm shaft. A worm-receiving cavity, hereinafter referred to as a worm cavity, is formed in the speed reducer housing. Similarly, a worm gear-receiving cavity, hereinafter referred to as a worm gear cavity, is formed in the speed reducer housing and a worm shaft-receiving bore, hereinafter referred to as a worm shaft bore, is also formed in said speed reducer housing. 
   The worm gear is mounted on a worm gear shaft and a worm gear shaft opening is formed in the second solid block to receive the worm gear shaft. 
   The worm shaft bore is discontinuous at the worm cavity. The worm shaft bore has a first part extending from the worm cavity to a first edge wall of the speed reducer housing and has a second part extending from the worm cavity to an opposed, second edge wall of the speed reducer housing. 
   A worm shaft is positioned in the worm shaft bore. In a first configuration, a first end of the worm shaft extends from the first edge wall of the speed reducer housing and in a second configuration, the first end of the worm shaft extends from the second edge wall of the speed reducer housing. 
   An outer end of the worm shaft is adapted to engage an output shaft of a motor means so that the output shaft rotates the worm shaft and hence the worm, and the worm rotates the worm gear and hence the worm gear shaft. 
   The worm cavity, the worm gear cavity, the worm shaft bore, and the worm gear shaft opening are each formed by a CNC machine-controlled milling process. Each cavity is a recess in the first or second metallic blocks, and confronting recesses collectively form a cavity. 
   Fastening means are provided for maintaining the first and second solid blocks in confronting relation to one another. The fastening means includes a first plurality of fastening bores formed in the first solid block and a second plurality of fastening bores formed in the second solid block. Fastener pins having their respective opposite ends press fit into said fastening bores align the first and second solid blocks and secure them to one another. The first and second plurality of fastening bores are formed by a computer-controlled milling process. 
   Gear lash and end play are controlled because the worm cavity is only slightly larger than the worm and the worm gear cavity is only slightly larger than the worm gear. 
   In a second embodiment, a double speed reducer includes a first solid block of metallic construction and a second solid block of metallic construction having a common width, height, and thickness as the first solid block. The first solid block and said second solid block form a first speed reducer housing when disposed in confronting relation to one another. 
   A first worm cavity is formed in the first speed reducer housing and a first worm is disposed in the first worm cavity. The first worm is mounted on a first worm shaft. 
   A first worm gear cavity is formed in the first speed reducer housing and a first worm gear is disposed in the first worm gear cavity in meshing relation to the first worm. 
   The first worm gear is mounted on a first worm gear shaft and a first worm gear shaft opening is formed in the second solid block to receive the first worm gear shaft. 
   A first worm shaft bore is formed in the first speed reducer housing. The first worm shaft bore is discontinuous at the first worm cavity. An outer part of the first worm shaft bore extends from the first worm cavity to a first edge wall of the first speed reducer housing and an inner part extends from the first worm cavity to a preselected point in spaced relation to a second edge wall of the first speed reducer housing. 
   The first worm shaft is positioned in the first worm shaft bore. An outer end of the first worm shaft is adapted to engage an output shaft of a motor means so that the output shaft rotates the first worm shaft and hence the first worm. The first worm rotates the first worm gear and hence the first worm gear shaft. 
   The double speed reducer further includes a third solid block of metallic construction and a fourth solid block of metallic construction having a common width, height, and thickness as said third solid block. The third solid block and the fourth solid block form a second speed reducer housing when disposed in confronting relation to one another. 
   The first speed reducer housing and the second speed reducer housing are disposed in abutting relation to one another. More particularly, a front wall of the first speed reducer housing abuts a first edge wall of the second speed reducer housing. 
   A second worm cavity is formed in the second speed reducer housing and a second worm is disposed in the second worm cavity. The second worm is mounted on a second worm shaft. 
   A second worm gear cavity is formed in the second speed reducer housing and a second worm gear is disposed in the second worm gear cavity in meshing relation to the second worm. 
   The second worm gear is mounted on a second worm gear shaft. A second worm gear shaft opening is formed in the fourth solid block to receive the second worm gear shaft. 
   A second worm shaft bore is formed in the second speed reducer housing. The second worm shaft bore is discontinuous at the second worm cavity and has an outer part extending from the second worm cavity to the first edge wall of the second speed reducer housing and has an inner part extending from the second worm cavity to a preselected point in spaced relation to a second edge wall of the second speed reducer housing. 
   The second worm shaft is positioned in the second worm shaft bore. 
   An outer end of the second worm shaft is adapted to engage the first worm gear shaft so that rotation of the first worm gear shaft rotates the second worm shaft and hence the second worm. The second worm rotates the second worm gear and hence the second worm gear shaft. The second worm gear shaft extends through a second worm gear shaft opening formed in the fourth solid block. The second worm gear shaft serves as a power take off shaft for the double speed reducer. 
   As in the single speed reducer embodiment, gear lash and end play are controlled because the first worm cavity is only slightly larger than the first worm, the first worm gear cavity is only slightly larger than the first worm gear, the second worm cavity is only slightly larger than the second worm, and the second worm gear cavity is only slightly larger than the second worm gear. 
   The primary object of this invention is to provide a new method for manufacturing speed reducers that eliminates the need to mold individual parts thereof. 
   A more specific object is to provide a new method where a CNC machine is employed to make a speed reducer. 
   Another object is to disclose a single speed reducer and a double speed reducer having a worm and worm gear power train where gear lash and end play are both controlled as a benefit of the novel manufacturing method. 
   Another object of this invention is to provide speed reducers that rely upon worms and worm gears to the exclusion of sprocket gears, sprocket chains, belts, pulleys, and the like. 
   A closely related object is to provide speed reducers that operate quietly and smoothly. 
   Another important object is to provide speed reducers employing worms and worm gears that maintain their designed gear lash and end play over many cycles of operation. 
   Yet another object is to disclose a new way to manufacture worm and worm gear speed reducers in a way that ensures meeting the object of the preceding paragraph. 
   These and other important objects, advantages, and features of the invention will become clear as this description proceeds. 
   The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: 
       FIG. 1  is a front perspective view of a speed reducer of the prior art; 
       FIG. 2  is a front elevational view of the first and second housings of a first embodiment of the present invention arranged in a first configuration; 
       FIG. 3  is a front elevational view of said first and second housings arranged in a second configuration of the first embodiment; 
       FIG. 4  is a perspective view of the first housing of the first embodiment; 
       FIG. 5  is a perspective view of the second housing of the first embodiment; 
       FIG. 6  is a sectional view taken along line  6 — 6  in  FIG. 4 ; 
       FIG. 7  is a sectional view taken along line  7 — 7  in  FIG. 5 ; 
       FIG. 8  is a sectional view taken along line  8 — 8  in  FIG. 5 ; 
       FIG. 9  is a perspective view of a second embodiment; 
       FIG. 10  is a front elevational view of the first and second housings of the first worm and worm gear assembly of the second embodiment arranged in a first configuration; 
       FIG. 11  is a perspective view of said first housing depicted in  FIG. 10 ; 
       FIG. 12  is a perspective view of said second housing depicted in  FIG. 10 ; 
       FIG. 13  is a perspective, partially exploded assembly view depicting a first configuration of the motor mount in said second embodiment; 
       FIG. 14  is an end elevational view of the  FIG. 13  embodiment when assembled in a first configuration and with a motor means in phantom lines; 
       FIG. 15  is an end elevational view of the  FIG. 13  embodiment when assembled in a second configuration where the output shaft of the lift extends in the same direction as the motor means; 
       FIG. 16  is an end elevational view of the  FIG. 13  embodiment when assembled in a third configuration where the output shaft of the lift extends in a direction perpendicular to the direction of the motor means; 
       FIG. 17  is a front elevational view of the first and second housings of the second worm and worm gear assembly of the second embodiment; and 
       FIG. 18  is a perspective view of the first and second housings of the second worm and worm gear assembly depicted in  FIG. 17 . 
   

   DETAILED DESCRIPTION 
   Referring now to  FIG. 1 , it will there be seen that a prior art speed reducer assembly of the belt and pulley type is denoted as a whole by the reference numeral  10 . Assembly  10  includes motor  12 , first pulley  14  mounted on output shaft  16  of said motor, second pulley  18 , belt  20  interconnecting first pulley  14  and second pulley  18 , pulley shaft  22  that rotates conjointly with second pulley  18 , speed reducing gear housing  24  that houses a gear train, not shown, and a power take off shaft  26  that may be employed for many lifting purposes such as, but not limited to, boat lifting. 
   A safety cover, not shown, is commonly provided to cover belt  20  and pulleys  14 ,  18 . 
   Speed reducer assemblies of this type have limited lifting capacity due to the slippage of belt  20  with respect to pulleys  14 ,  18 . They also lack a self-locking feature and the lifted item may therefore gradually lower over time due to the phenomena of inertia-generated coasting. Moreover, power increases with speed reduction, but such systems have limited speed reduction and thus limited lifting power. 
   Referring now to  FIGS. 2 and 3 , it will there be seen that the reference numeral  30  denotes a first embodiment of the present invention. This first embodiment is a single speed reduction system and employs a single worm and worm gear assembly. 
   Significantly, as is clear from a comparison of  FIGS. 2 and 3 , the worm shaft of this first embodiment may be arranged in a first position extending to the left as depicted in  FIG. 2  or in a second position extending to the right as depicted in  FIG. 3 . This flexibility is a function of the off-center mounting of worm  42  relative to worm shaft  46 . Worm  42  divides worm shaft  46  into an elongate part and a truncate part. The elongate part of worm shaft  46  extends outwardly from a first side of the speed reducer housing in the configuration of  FIG. 2  and outwardly from a second, opposite side of the speed reducer housing in the configuration of  FIG. 3 . The truncate part of worm shaft  42  is disposed interiorly of single speed reducer  30  in both configurations. If an obstacle is encountered during installation of the novel speed reducer, the novel structure of the speed reducer enables worm shaft  46  to be re-configured and such re-configuration in some cases may enable an installation to be accomplished in a space where it could not have been accomplished but for the off-center mounting and the flexibility thereby provided. 
   Single speed reducer  30  includes first block  32  and second block  34 . As indicated by arcuate assembly arrow  33  in  FIGS. 2 and 3 , the first and second blocks are placed into juxtaposition with one another to form a housing. Each block begins as a solid metal block and each block is milled to accommodate a worm, a worm shaft, and a worm gear. One of the blocks is milled to include a worm gear shaft opening, as will be fully explained hereinafter. 
   As best understood by comparing  FIGS. 2–4 , first housing  32  includes circular worm gear recess  36  formed therein to accommodate worm gear  38 , rectangular worm recess  40  to accommodate worm  42  and thrust bearings  43 , and a pair of straight worm shaft grooves  44   a ,  44   b  ( FIG. 4 ). Rectangular worm recess  40  has a greater depth than that of circular worm gear recess  36 . Worm shaft groove  44   a  accommodates worm shaft  46  when the assembly is in the configuration depicted in  FIG. 2 , and worm groove  44   b  accommodates worm shaft  46  when the assembly is in the configuration of  FIG. 3 . This optional mounting of worm shaft  46  enables an installer increased flexibility when installing single speed reducer  30  in a small space. 
   As best understood by comparing  FIGS. 2–5 , second housing  34  has circular worm gear recess  48  formed therein to accommodate worm gear  38 , rectangular worm recess  50  to accommodate worm  42  and thrust bearings  43 , straight worm shaft grooves  52   a ,  52   b  to accommodate worm shaft  46  when in its  FIG. 2  and  FIG. 3  configurations, respectively, and hub  54  that centers worm gear  38 . Rectangular worm recess  50  has a depth greater than that of circular worm gear recess  48 . 
   Hub  54  is centrally apertured to form worm gear shaft opening  55  to accommodate a worm gear shaft, not depicted, that is keyed to worm gear  38  for conjoint rotation therewith. Recess  57   a , formed in block  32 , accommodates hub  54  and recess  57   b , also formed in block  32  in concentric relation to recess  57   a , accommodates an innermost end of said unillustrated worm gear shaft. 
   The unillustrated worm gear shaft extends through worm gear shaft opening  55  and thus extends externally of the housing formed by the juxtapositioning of blocks  32  and  34 . Said worm gear shaft is therefore understood to be the power take-off shaft of this single speed reducer. 
   A plurality of blind bores, collectively denoted  35   a  in first housing  32  and  35   b  in second housing  34 , receive opposite ends of mounting pins, not shown, that interconnect said first and second housings to one another in sandwiching relation to worm  42  and worm gear  38  when single speed reducer  30  is assembled. 
   Machining two solid aluminum blocks with a CNC machine preferably forms first and second housings  32  and  34 . The gear, shaft, and bearing-accommodating recesses and grooves may thus be machined to a close tolerance, thereby maintaining a designer-preselected gear lash and end play. The recesses and grooves are also sized to accommodate oil seals as may be required. 
   When first and second housings  32  and  34  are in confronting relation to one another, circular worm gear recesses  36  and  48  collectively form a worm gear cavity. Rectangular worm recesses  40  and  50  collectively form a worm cavity. Worm shaft grooves  44   a ,  44   b  and  52   a ,  52   b , collectively form a worm shaft bore that is discontinuous at the worm cavity. 
   A second embodiment is denoted as a whole by the reference numeral  60  in  FIG. 9 . Second embodiment  60  is a double speed reducer. It includes a first speed reducer  62  and a second speed reducer  64 . 
   Significantly, double speed reducer  60  has three (3) distinct configurations, thereby facilitating its installment in locations where space may be limited. A first configuration is depicted in  FIGS. 9–11 , a second configuration is depicted in  FIG. 12 , and a third configuration is depicted in  FIG. 13 . 
   More particularly,  FIG. 1  is a side elevational view of the assembly depicted in  FIGS. 9 and 10 .  FIG. 12  is a side elevational view of a second configuration of double speed reducer  60  where speed reducer  62  is rotated one hundred eighty degrees (180°) from the position thereof in  FIGS. 9–11 .  FIG. 13  is a side elevational view of a third configuration of double speed reducer  60  where speed reducer  62  and motor  12  are rotated ninety degrees (90°) upwardly from the position thereof in  FIGS. 9–11  as indicated by directional arrow  13  in  FIG. 12 . 
   First speed reducer  62  includes a housing formed of first block  64  and second block  66 . Second speed reducer  68  includes a housing formed of first block  70  and second block  72 . 
   Before describing the structure of double speed reducer  60  in detail, a brief overview of its structure is provided in connection with  FIG. 9 . An output shaft, not shown, of motor  12  is keyed for conjoint rotation with a worm shaft, not shown, that carries a worm. It will be surmised from  FIG. 9  that said worm is positioned in a first hollow worm cavity formed when blocks  64  and  66  are placed in confronting relation to one another and that said worm cavity is toward the lower end of speed reducer  62 . Moreover, a bore that extends to said cavity to accommodate said worm shaft is formed by a pair of confronting semicircular grooves, not shown in  FIG. 9 . A second hollow cavity is similarly formed from the juxtaposition of said blocks  64  and  66 , said second hollow cavity accommodating a worm gear, also not shown, that is in meshing relation to the worm positioned below it. The worm gear of speed reducer  62  is mounted on a worm gear shaft, not shown, that extends through a worm gear shaft opening formed in block  66 . That worm gear shaft is received within a worm gear shaft bore formed in second speed reducer  68 , said worm gear shaft bore being formed by a pair of confronting semicircular grooves formed in blocks  70  and  72 . The worm gear shaft is keyed for conjoint rotation with a worm-carrying worm shaft that is accommodated within a worm cavity formed in the upper part of speed reducer  68 , said cavity being confluent with the worm gear shaft bore that accommodates the worm gear shaft of speed reducer  62  and the worm gear shaft of speed reducer  68 . Just below the worm cavity of speed reducer  68  is a worm gear cavity formed by the juxtaposition of blocks  70  and  72 . A worm gear positioned within that worm gear cavity is mounted to worm gear shaft  74  that extends through a worm gear shaft opening formed in block  72  of speed reducer  68 . Collar  75  is mounted to said worm gear shaft  74 . Thus it is understood that worm gear shaft  74  is the power take off shaft for double speed reducer  60 . Said shaft  74  rotates slowly but with high torque and as such may be used advantageously in applications where a heavy weight it to be raised or lowered at a relatively slow pace. Boatlifts, for example, often require slow speed and high torque, but the novel apparatus is not limited to boatlift applications. 
   The means for connecting motor  12  to first reducer  62  is best understood in connection with  FIG. 10 . Motor mounting plate  76  having hub  77  is secured by a plurality of fastening members, collectively denoted  78 , to a sidewall or edge wall of first speed reducer  62  as indicated by the assembly lines. A leading end of coupler  73  ensleeves and engages worm shaft  79  that extends from bore  65  formed in said sidewall of speed reducer  62 . A trailing end of coupler  73  ensleeves and engages the output shaft of motor  12  so that rotation of said output shaft imparts simultaneous and corresponding rotation to worm shaft  79 . 
   The construction of speed reducer  62  is further depicted in  FIGS. 14 and 15 . 
   Speed reducer  62  includes first solid block  64  and second solid block  66 . As indicated by arcuate assembly arrow  65  in  FIG. 14 , the first and second solid blocks are placed into juxtaposition with one another to complete the assembly. 
   First block  64  has circular worm gear recess  80  formed therein to accommodate worm gear  82 . Hub  81  is centered with respect to circular worm gear recess  80 . Hub  81  is centrally apertured as at  83  to accommodate a worm gear shaft that extends into a worm shaft bore, disclosed hereinafter, formed in speed reducer  68 . 
   Rectangular worm recess  84  is formed in first block  64  to accommodate worm  86  and thrust bearings  88  and has a depth greater than the depth of circular worm gear recess  80 . Groove  65   a  is formed in block  64  and its outer end is in open communication with worm shaft bore  65 . Its inner, closed end is denoted  65   b . Groove  65   b  is a blind groove, having in outer end in open communication with worm recess  84  and an inner end that accommodates the inner end of worm shaft  79 . 
   Second block  66  has circular worm gear recess  92  formed therein to accommodate worm gear  82 , rectangular worm recess  94  to accommodate worm  86  and thrust bearings  88 , and straight worm shaft grooves  65   c ,  65   d  to accommodate worm shaft  79 . Rectangular worm recess  94  has a depth greater than the depth of circular worm gear recess  92 . 
   A plurality of blind bores, collectively denoted  97   a  in first block  64  and  97   b  in second block  66 , receive opposite ends of mounting pins, not shown, that interconnect said first and second blocks to one another in sandwiching relation to worm  86  and worm gear  82  when housing  62  is assembled. 
   Machining two solid aluminum blocks with a CNC machine forms first and second blocks  64  and  66 . The gear, shaft, and bearing-accommodating recesses and grooves may thus be machined to a close tolerance, thereby maintaining a designer-preselected gear lash and end play. The recesses and grooves are also sized to accommodate oil seals as may be required. 
   Blocks  70  and  72 , depicted in  FIGS. 16–18 , have a substantially similar construction. They are brought in confronting relation to one another is indicated by arcuate arrow  71  to form second speed reducer  68 . Block  70  has circular worm gear recess  104  formed therein to accommodate worm gear  106 . In block  72 , hub  108  centers said worm gear  106  within said circular worm gear recess  104 . Hub  108  is centrally apertured at worm gear shaft opening  109  to accommodate worm gear shaft  74  that serves as the power take off shaft for double speed reducer  60  as mentioned above. 
   Rectangular worm recess  110  accommodates worm  112  and thrust bearings  113 , worm shaft groove  114   a  (FIG.,  17 ) accommodates a first end of worm shaft  116  and worm shaft groove  114   b  accommodates a second end of worm shaft  116 . 
   Second housing  72  has circular worm gear recess  120  formed therein to accommodate worm gear  106 . Rectangular worm recess  122  accommodates worm  112 , worm shaft groove  124   a  accommodates an inner end of worm shaft  116  and worm shaft groove  124   b  accommodates an outer end of worm shaft  116 . 
   A plurality of blind bores, collectively denoted  126   a  in first block  70  and  126   b  in second block  72 , receive opposite ends of mounting pins  127 , two of which are depicted in  FIG. 18 , that interconnect said first and second blocks to one another in sandwiching relation to worm  112  and worm gear  106  when housing  68  is assembled. 
   Machining two solid aluminum blocks with a CNC machine forms first and second blocks  70  and  72 . The gear, shaft, and thrust bearing-accommodating recesses and grooves may thus be machined to a close tolerance, thereby maintaining a designer-preselected gear lash and end play. The recesses and grooves are also sized to accommodate oil seals as may be required. 
   It will thus be seen that the objects set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
   It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween. 
   Now that the invention has been described,