4/29/2014 Tutorial: How to model involute gears in SolidWorks and show design intent. - GrabCAD

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Steen Winther 12 months ago

The model from this tutorial is found here:

Involute Gear Design from Scratch

1. Step 1

1) Make a sketch with a circle on the front plane. This represents the pitch circle thatdefines the centre of the tooth in radial direction. Dimension it. I chose a Pitch

diameter, P=76 mm, but obviously you can choose any value.

2. Step 2

2) The module, m, expresses the size of the teeth and thus also the total number of

teeth and the overall size of the gear wheel. I chose m=2. Therefore the number of teeth, N, is N=P/m=76/2=38.

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3. Step 3

3) Draw a vertical construction line through the centre and a horizontal tangent to thecircle. The lines meet in the first point on the involute curve.

4. Step 4

4) Draw another construction line through this point at an angle of 20 degrees. This

angle is called the pressure angle and 20 degrees is one of the most used standards,

but it could be something else.

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5. Step 5

5) Draw a perpendicular construction line to the pressure angle line through the centre.

6. Step 6

6) Draw a construction circle through the centre and the point found in the previousstep. This circle is the base circle for the involute. As you may know, an involute is the

curve described by the end of a string wound around a cylinder. And the “string

length” is the distance shown in the next step:

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7. Step 7

7) Dimension that distance. (You have to make it driven in SolidWorks because the

length is fully defined by the sketch). If you change the sketch, this measurement will

update to a new value.

8. Step 8

8) I hide the sketch relations in this step to remove clutter from the images.

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9. Step 9

9) I will now construct the “virtual” string when it is “unwound” a little more. Draw a

centerpoint arc as indicated.

10. Step 10

10) Dimension it to a nice round number, e.g. 5. This has to be an ARC

DIMENSION. You click the two endpoints AND the arc itself, and the resultingdimension has a little arc over the number, showing that the dimension is measured

through the arc instead of linearly.

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11. Step 11

11) Now draw the radius and tangent through this new end point and dimension it.

12. Step 12

12) Press = when the dimension modify box is open to define an equation.

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13. Step 13

13) Click the dimension for the first part of the string (length 13 mm in my drawing).

This enters the value into the equation automatically.

14. Step 14

14) Click +

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15. Step 15

15) Click the dimension of the “new piece of string” (length 5 in my drawing).

16. Step 16

16) Click the green check mark in the dialog box. You’ll see that the new length is

calculated from the existing dimensions (length 18 mm in my drawing). The endpoint isanother point on the involute; and by changing the value of the arc, you can get ALL

POINTS on the top half of the involute through this “graphic calculator”.

4/29/2014 Tutorial: How to model involute gears in SolidWorks and show design intent. - GrabCAD

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17. Step 17

17) Do a similar construction with an arc going the opposite direction to obtain an

additional point on the involute.

18. Step 18

18) This time you subtract the arc length from the original value. You can also draw apoint offset the initial value (13) along the base circle to get the lowermost point on the

involute.

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19. Step 19

19) You can now draw the involute IN A NEW SKATCH using the constructed

points.

20. Step 20

20) Use the spline tool to draw a spline through the 3 or 4 constructed points.

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21. Step 21

21) Press ESC to end.

22. Step 22

22) Draw a construction line that represents the centre of the gear cog. It is offset ¼

of the angle for one cog. You can do the calculations by punching in the numbersdirectly into the “Modify Dimension” box as “=360/38/4”.

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23. Step 23

23) Mirror the involute by ctrl-clicking the spline and the centreline and choosing“Mirror Entities”.

24. Step 24

24) At this stage we need to draw the circle that defines the outer size of the gear. The

diameter is defined by P+2*m = 76 mm + 2*2 mm = 80 mm.

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25. Step 25

25) When you look closely, you see that the involute is a tiny bit too short to reach theouter contour. This needs to be fixed.

26. Step 26

26) Go back to the first sketch and right-click it to edit. Increase the length of the arcfrom 5 mm to say 5.5 mm. Due to the parametric nature of the software, everything

updates without you having to do anything else.

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27. Step 27

27) Return to the present sketch and verify that the involutes now extend beyond theouter diameter.

28. Step 28

28) Use Power trim to cut off excess parts of the involutes.

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29. Step 29

29) We need to add a small clearance for the teeth inside the involute diameter.Extend the tooth downwards with lines parallel to the normal construction line.

30. Step 30

30) I chose a .25 mm extension/clearance.

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31. Step 31

31) Mirror the profile.

32. Step 32

32) Draw the base (inner) circle.

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33. Step 33

33) We are now ready to extrude the gear. Make a new sketch on the front plane …

34. Step 34

34) … and choose “Convert Entities”

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35. Step 35

35) Select the inner circle and click the green check mark.

36. Step 36

36) Extrude the base cylinder. I chose a 12 mm wide gear wheel.

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37. Step 37

37) Make a new sketch on the front plane, choose “Convert Entities” again and check“Select chain”.

38. Step 38

38) Click on the gear tooth profile and click OK.

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39. Step 39

39) Do another extrude …

40. Step 40

40) … using the Up to surface and select the front face of the gear.

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41. Step 41

41) This is the result: The gear wheel with one tooth.

42. Step 42

42) Choose “Circular Pattern” to copy the tooth, select the outside face and the tooth

as “Feature to Pattern”. Specify 38 instances, equal spacing over 360 degrees andclick OK.

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43. Step 43

43) The gear wheel is almost complete.

44. Step 44

44) Cut away the centre with a 55 mm circle on the front face.

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45. Step 45

45) And “Cut-Extrude Through All” for improved visibility.

46. Step 46

46) Hide the sketches by selecting all and choosing “Hide” (the glasses).

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47. Step 47

47) Now comes the best part: Verification of the design. Save and choose “MakeAssembly from Part”.

48. Step 48

48) Click the green checkmark for OK. This gives an assembly with the gear wheel atthe origin.

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49. Step 49

49) Ctrl-drag a second copy of the gear wheel into the main window.

50. Step 50

50) Choose “View Temporary Axes” to show axes for mating.

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51. Step 51

51) Ctrl-select the two centre axes and click the mate (paperclip) icon that pops-up.

52. Step 52

52) Add a distance mate of 76 mm (= the pitch diameter) which is also the distance

between the gears when they have equal size.

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53. Step 53

53) Mate the temporary axis of the second gear to the assembly top plane …

54. Step 54

54) … and mate the front faces of both gear wheels.

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55. Step 55

55) We are now almost ready, but the first gear is fixed and can’t turn. Right-click onthe first gear wheel (the one with that has (f) in front of its name) and choose “Float”.

56. Step 56

56) Now it can move everywhere so we need to fix it so it can only rotate. Mate thetemporary axis to the assembly top plane …

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57. Step 57

57) … Mate the temporary axis to the right plane …

58. Step 58

58) … and the front plane to the assembly front plane. Now both gear wheels canrotate independently but they stay centered.

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59. Step 59

59) Go to a front view and zoom into the teeth that mesh.

60. Step 60

60) We need to cheat a little bit to make the next step work, because the gears are

too perfect and are always touching.

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61. Step 61

61) Right-click on the distance mate and change it by a small amount …

62. Step 62

62) … e.g. from 76 to 76.1 mm. This gives a little slack that’s necessary for the nextsteps to initiate.

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63. Step 63

63) Rotate one of the gear wheels so they do not touch.

64. Step 64

64) Choose “Tools->Component->Move” from the top menu.

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65. Step 65

65) Click the radio button for “Physical Dynamics”.

66. Step 66

66) Click and drag one of the gears, and observe that the other gear follows alongand the involutes mesh very nicely. You can go backwards and forwards. This is SOCOOL :-)

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67. Step 67

67) We’re done. We have designed involute gears and verified that they actually workaccording to design intent.

1. Miguel 10 days ago

Hi. At step16 i get a massage ''The syntax o equation is incorrect''. Can you help

solve this please?