Levers and Gears

    Backing Plate

  1. Create a new part.
  2. Create an Extruded Base on the Front plane.
  3. Draw a 6 inch by 6 inch square in the sketch, and extrude to a depth of 1/8 inch.
  4. Edit the sketch and place a circle inside the square; dimension it to 1/8 inch diameter.
  5. Set the dimension precision to three digits (.123).
  6. Place a second circle two inches to the right of the first one.
  7. Make the circles Equal.
  8. Exit the sketch and color the part brown.
  9. Save the part as BackingPlate.SLDPRT.

    Lever

  10. Create a new part.
  11. Create an Extruded Base on the Front plane.
  12. Draw a horizontal slot starting at the origin.
  13. Dimension the slot radius to 1/8 inch. (Note that this is a radius, not a diameter.)
  14. Set the dimension precision to three digits (.123).
  15. Dimension the slot length to 3 inches.
  16. Draw a circle at the center of each arc, and at the midpoint of the slot.
  17. Make all the circles Equal.
  18. Dimension the left circle to a diameter of 1/8 inch.
  19. Set the dimension precision to three digits (.123).
  20. Exit the sketch and extrude to a depth of 1/8 inch.
  21. Color the entire part red.
  22. Save the part as Lever.SLDPRT.

    Spacer

  23. We don't want the lever to rest against the backing plate because that won't leave room for the fasteners. Therefore, we need to create a spacer.
  24. Start a new part and create an Extruded Base on the Front plane.
  25. Draw a circle centered on the origin with diameter 1/4 inch.
  26. Draw a circle inside it, centered on the origin, with diameter 1/8 inch.
  27. Exit the sketch and set the extrude depth to 1/8 inch.
  28. Save you part as Spacer.SLDPRT.

    First Assembly

  29. Create a new Assembly.
  30. Insert the BackingPlate as the first part. Note that it is Fixed (f) by default.
  31. Insert a Spacer as the second part.
  32. Mate the bottom edge of the hole in the spacer to the left hole in the backing plate. Because the diameters are equal, this will be a Coincident mate.

  33. Insert a Lever as the third part.
  34. Mate the center hole of the lever to the spacer by selecting the back edge of the lever hole and the front edge of the spacer hole. You should be able to use a Coincident mate.
  35. Now you can click and drag on the lever and it will pivot about the center hole, like a real lever.

  36. Insert a second Spacer and Lever.
  37. Mate the second spacer's hole to the right hole in the backing plate.
  38. Mate the second level's middle hole to the second spacer.
  39. Note that the second lever also pivots, but when the two levers collide they pass right through each other.

    Scissors Mechanism

  40. Insert a third lever.
  41. Connect the third lever to the first one by mating the bottom edge of the third lever's center hole to the top edge of the first lever's center hole.
  42. Mate the bottom edge of the third lever's right hole to the top edge of the second lever's left hole.
  43. Insert a fourth lever.
  44. Connect the fourth Lever to the second one by mating the bottom edge of the fourth lever's center hole to the top edge of the second lever's center hole.
  45. Mate the bottom edge of the fourth Lever's left hole to the top edge of the first lever's right hole.
  46. Note that we cannot move the mechanism now. That is because it is fixed to the backing plate in two locations.
  47. Edit the second lever's mates and remove its coincident mate to the backing plate.
  48. Now we can move any lever and the entire mechanism changes shape. But it's underconstrained so it moves in a cockeyed fashion.

    Constrained Motion: Slot Mate

  49. Return to the BackingPlate part and edit the sketch.
  50. Delete the right circle.
  51. Draw a horizontal slot to the right of the remaining circle.
  52. Add a Coincident relation between the center of the circle and the construction line of the slot, if it's not already there.
  53. Dimension the slot radius to 1/16 inch.
  54. Set the dimension precision to 4 digits (.1234).
  55. Dimension the length of the slot's construction line to 2.5 inches.
  56. Dimension the distance between the center of the circle and the left edge of the slot's construction line to 0.25 inches.
  57. Save the part and return to the assembly.

  58. Click on the mate tool.
  59. Scroll down to the Mechanical Mates section and open it.
  60. Select Slot Mate.
  61. In the graphics window, select the face of the third lever's hole, then select one of the long faces of the slot in the backing plate.
  62. Click the green check mark to accept the mate.
  63. Now moving any of the levers causes constrained motion of the mechanism: it's restricted to moving along the path of the slot.

  64. Add two more levers to extend the scissors. You do not need another slot mate, just four coincident mates.
  65. Save the assembly as Scissors.SLDASM.

    Gears

  66. Download this SpurGear-6-20.SLDPRT gear part.
  67. The 6 is the diametral pitch of the gear (teeth per inch). The 20 is the number of teeth.
  68. Open the part.

    New Backing Plate

  69. Make a new backing plate 12 inches square.
  70. Add two 1/8 inch diameter holes connected by a horizontal centerline.
  71. Dimension the centerline to 3.36 inches.
  72. Draw a diagonal centerline from the center of the left hole down and to the left.
  73. Dimension the diagonal centerline length to 2.7 inches, and the interior angle between it and the horizontal centerline to 135 degrees.
  74. Draw a new circle centered on the left endpoint of the diagonal centerline, and make it Equal to the other circles.
  75. Save the part as BackingPlate2.SLDPRT.

    12 tooth Gear

  76. Go to the SpurGear window.
  77. Right click on Equations in the Feature Manager tree and select Manage Equations.
  78. Set the variable NumberTeeth to 12.
  79. Click OK to exit the equation manager.
  80. Do File > Save As and resave the file (save as copy) as SpurGear12.SLDPRT.

    Gear Assembly

  81. Create a new assembly.
  82. Insert BackingPlate2 as the first part.
  83. Insert three Spacers into the assembly and mate them to the holes in the backing plate.
  84. Insert a SpurGear and mate its central hole to the left spacer of the horizontal pair in the backing plate.
  85. Insert a second SpurGear and mate its central hole to the right spacer of the horizontal pair in the backing plate.
  86. Notice that although the gears are "meshed", spinning one has no effect on the other.
  87. Rotate the gears until the teeth are meshed and don't overlap.

    Gear Mate

  88. Click on the mate tool.
  89. Scroll down to the Mechanical Mates section and open it.
  90. Select Gear mate.
  91. Click on the inner face of the central hole of each gear.
  92. Set the tooth ratio to 20:20.
  93. Click the green checkmark to accept the mate.
  94. Now rotating one gear causes the other to turn in the opposite direction.

  95. Insert a SpurGear12 part and mate it to the remaining spacer.
  96. Create a gear mate between the 12 tooth gear and the adjacent 20 tooth gear. Set the tooth ratio to 12:20.
  97. Note: if you need to adjust the phase of the gears, open the mates in the feature manager tree, suspend one of the gear mates, rotate the gears, and then un-suspend the gear mate.
  98. Save the assembly as Gears.SLDASM.
    TO DO: add spacers to prevent link collisions.

    Make an Arm

  99. Create a new part.
  100. Create an Extruded Base on the Front plane.
  101. Draw a horizontal slot running rightward from the origin, with a radius of 1/8 inch and a length of 1.5 inches.
  102. Put a 1/8 inch diameter circle at the right endpoint of the slot.
  103. Extrude to a depth of 1/8 inch.

  104. Create another Extruded Base, also on the Front plane.
  105. Draw a diagonal slot running upward and to the left from the origin. The two slots will overlap at the origin.
  106. Dimension the slot radius to be the same as the other slot: expose the other slot's sketch and use an Equal relation.
  107. Dimention the slot length to be 1 inch.
  108. Dimension the angle between the two slot centerlines to 135 degrees.
  109. Add a circle to the left endpoint of the centerline, and make it equal in diameter to the circle in the previous sketch.
  110. Click OK to exit the sketch.
  111. Make sure the "Merge Result" box is checked and extrude to a depth of 1/8 inch.
  112. Color the part red.
  113. Save the part as Arm.SLDPRT.

    Make a Torso

  114. Create a new part.
  115. Create an Extruded Base on the Front plane.
  116. Create a vertical construction line 4 inches high.
  117. Using the spline tool, draw the left half of the profile of a person's head and torso.
  118. Connect the bottom of the torso to the origin with a horizontal line.
  119. Put a 1/8 inch diameter circle in the approximate location of the armpit.
  120. Use the Mirror Entities tool to mirror the spline, the hole, and the horizontal line about the vertical construction line.
  121. Exit the sketch and extrude to a depth of 1/8 inch.
  122. Color the part yellow.
  123. Save the part as Torso.SLDPRT.
  124. Insert the torso into the Gears assembly.
  125. Insert two arms into the assembly and connect the short segment of each arm to the shoulder by mating the back circle of the arm hole with the front circle of the shoulder hole. This forces the arms to lie in front of the torso.

    Make a Link

  126. Create a new part.
  127. Create an Extruded Base on the Front plane.
  128. Draw a slot with a 1/8 inch radius, 5 inches long.
  129. Draw a circle centered on each endpoint of the slot, dimensioned to 1/8 inch diameter.
  130. Extrude to a depth of 1/8 inch.
  131. Save the part as Link.SLDPRT.

    Connect the Torso to the Gears

  132. Insert a Link into the assembly.
  133. Mate the front circle of one link hole to the back circle of the hole at the end of the left arm, forcing the link to lie behind the arm.
  134. Mate the other hole in the link to the outermost hole in the left spur gear. You will need to use a Concentric mate for this, as a Coincident mate will overdefine the assembly.
  135. Add second link to connect the other arm to the other spur gear.
  136. Verify that the arms move properly when you spin the gears. You can adjust the phase of the arms by temporarily suspending the gear mate and moving one gear.
  137. You can use a Lock mate to lock the torso to a specific position relative to the backing plate.
  138. Save your modified assembly.

Dave Touretzky
Last modified: Wed Mar 29 05:32:27 EDT 2017