Patent Publication Number: US-2013233108-A1

Title: Combination Double Thread Screw

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a double thread screw and, more particularly, to a combination double thread screw for a precision transmission apparatus or a motorized mechanism. 
     2. Description of the Related Art 
     A conventional double thread screw comprises an elongate rod and two intersecting threads (rightward helical thread and leftward helical thread) formed on the elongate rod. The two threads are arranged successively in a staggered manner and are directed in two opposite threading directions. In operation, a nut is screwed onto the double thread screw. Thus, when the double thread screw is driven and rotated, the nut is moved on the double thread screw reciprocally by provision of the two threads. The double thread screw is available for a precision transmission apparatus or a motorized mechanism. The two intersecting threads are formed on the elongate rod by turning. However, the working process of the two intersecting threads is complicated and difficult, thereby increasing the cost of fabrication. In addition, the double thread screw has determined specifications and sizes so that the double thread screw cannot fit a requirement of different specifications and sizes, thereby limiting the versatility of the double thread screw. Further, when a user needs to have a double thread screw of different specification and size, he has to order and design the double thread screw additionally and previously and has to wait the product for a long period of time, thereby wasting the time and increasing the cost of fabrication. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a double thread screw, comprising a mandrel, a plurality of threaded blocks mounted on the mandrel, and two ends stops mounted on the mandrel to limit the threaded blocks. The mandrel is a polygonal elongate bar and has a periphery provided with a plurality of locking faces which are connected with each other. The threaded blocks are clamped between and limited by the ends stops. Each of the threaded blocks has a central portion provided with a locking hole locked onto the locking faces of the mandrel. The locking hole of each of the threaded blocks has a polygonal shape. Each of the threaded blocks has a periphery provided with two first thread grooves which intersect each other. The first thread grooves of each of the threaded blocks have two opposite threading directions. The first thread grooves of the threaded blocks are combined to form two intersecting threads which are arranged successively in a staggered manner and are directed in two opposite threading directions. 
     Each of the threaded blocks has two beveled faces formed on two opposite ends thereof. Each of the threaded blocks has a first side provided with a wide portion located between the beveled faces and a second side provided with a narrow portion located between the beveled faces. The wide portion of each of the threaded blocks has a width greater than that of the narrow portion. The wide portion of one of the threaded blocks is juxtaposed to the narrow portion of another one of the threaded blocks so that the wide portions and the narrow portions of the threaded blocks are arranged successively in a staggered manner. The beveled faces of the threaded blocks engage each other, and the first thread grooves of the threaded blocks are connected with each other. 
     Each of the ends stops is a bushing. Each of the ends stops has a central portion provided with a locking bore locked onto the locking faces of the mandrel. The locking bore of each of the ends stops has a polygonal shape. Each of the ends stops has an end portion provided with a beveled surface. Each of the ends stops has a periphery provided with two second thread grooves which intersect each other. The second thread grooves of each of the ends stops have two opposite threading directions. The beveled surface of each of the ends stops engages one of the beveled faces of a respective one of the threaded blocks, and the second thread grooves of each of the ends stops are connected to the first thread grooves of a respective one of the threaded blocks. 
     The primary objective of the present invention is to provide a double thread screw whose length can be changed. 
     According to the primary advantage of the present invention, the number of the threaded blocks can be changed to construct the double thread screw with different length, so that the size of the double thread screw can be adjusted freely by changing the number of the threaded blocks so as to fit the requirements of different users, thereby enhancing the versatility of the double thread screw, and thereby decreasing the cost of fabrication. 
     According to another advantage of the present invention, the size of the double thread screw can be adjusted by changing the number of the threaded blocks so that the manufacturer needs not to prepare and store double thread screws of different sizes and specifications, thereby greatly decreasing the cost of storage. 
     Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  is a perspective view of a double thread screw in accordance with the preferred embodiment of the present invention. 
         FIG. 2  is an exploded perspective view of the double thread screw as shown in  FIG. 1 . 
         FIG. 3  is a front view of the double thread screw as shown in  FIG. 1 . 
         FIG. 4  is a front cross-sectional view of the double thread screw as shown in  FIG. 3 . 
         FIG. 5  is a top view of the double thread screw as shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings and initially to  FIGS. 1 and 2 , a double thread screw  1  in accordance with the preferred embodiment of the present invention comprises a mandrel  10 , a plurality of threaded blocks  20  mounted on the mandrel  10 , and two ends stops  30  mounted on the mandrel  10  to limit the threaded blocks  20 . 
     The mandrel  10  is a polygonal elongate bar and has a periphery provided with a plurality of locking faces  11  which are connected with each other. 
     The threaded blocks  20  are clamped between and limited by the ends stops  30 . Each of the threaded blocks  20  has a central portion provided with a locking hole  21  locked onto the locking faces  11  of the mandrel  10  so that each of the threaded blocks  20  is combined with the mandrel  10  to rotate in concert with the mandrel  10 . The locking hole  21  of each of the threaded blocks  20  has a polygonal shape. Each of the threaded blocks  20  has a periphery provided with two first thread grooves  25  which intersect each other. The first thread grooves  25  of each of the threaded blocks  20  have two opposite threading directions. Each of the threaded blocks  20  has two beveled faces  22  formed on two opposite ends thereof. Each of the threaded blocks  20  has a first side provided with a wide portion  23  located between the beveled faces  22  and a second side provided with a narrow portion  24  located between the beveled faces  22 . The wide portion  23  of each of the threaded blocks  20  has a width greater than that of the narrow portion  24 . 
     Each of the ends stops  30  is a bushing. Each of the ends stops  30  has a central portion provided with a locking bore  31  locked onto the locking faces  11  of the mandrel  10 . The locking bore  31  of each of the ends stops  30  has a polygonal shape. Each of the ends stops  30  has an end portion provided with a beveled surface  32 . Each of the ends stops  30  has a periphery provided with two second thread grooves  33  which intersect each other. The second thread grooves  33  of each of the ends stops  30  have two opposite threading directions. 
     In assembly of the double thread screw  1 , referring to  FIGS. 3-5  with reference to  FIGS. 1 and 2 , the threaded blocks  20  are mounted on the mandrel  10  serially with the locking hole  21  of each of the threaded blocks  20  being locked onto the locking faces  11  of the mandrel  10 . At this time, the wide portion  23  of one of the threaded blocks  20  is juxtaposed to the narrow portion  24  of another one of the threaded blocks  20  so that the wide portions  23  and the narrow portions  24  of the threaded blocks  20  are arranged successively in a staggered manner. In addition, the beveled faces  22  of the threaded blocks  20  engage each other, and the first thread grooves  25  of the threaded blocks  20  are interconnected with each other. Then, each of the ends stops  30  is mounted on the mandrel  10  with the locking bore  31  of each of the ends stops  30  being locked onto the locking faces  11  of the mandrel  10 . At this time, the beveled surface  32  of each of the ends stops  30  engages one of the beveled faces  22  of a respective one of the threaded blocks  20 , and the second thread grooves  33  of each of the ends stops  30  are connected to the first thread grooves  25  of a respective one of the threaded blocks  20 . Thus, the mandrel  10 , the threaded blocks  20  and the ends stops  30  are combined together to construct the double thread screw  1 , and the first thread grooves  25  of the threaded blocks  20  and the second thread grooves  33  of the ends stops  30  are interconnected and combined to form two intersecting threads  2  which are arranged successively in a staggered manner and are directed in two opposite threading directions. At this time, the threaded blocks  20  are clamped between and limited by the ends stops  30  so that the threaded blocks  20  will not be detached from the mandrel  10 . 
     Accordingly, the number of the threaded blocks  20  can be changed to construct the double thread screw  1  with different length, so that the size of the double thread screw  1  can be adjusted freely by changing the number of the threaded blocks  20  so as to fit the requirements of different users, thereby enhancing the versatility of the double thread screw  1 , and thereby decreasing the cost of fabrication. In addition, the size of the double thread screw  1  can be adjusted by changing the number of the threaded blocks  20  so that the manufacturer needs not to prepare and store double thread screws  1  of different sizes and specifications, thereby greatly decreasing the cost of storage. 
     Although the invention has been explained in relation to its preferred embodiment(s) as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention. It is, therefore, contemplated that the appended claim or claims will cover such modifications and variations that fall within the true scope of the invention.