Tutorial RD

8/10/2019 Tutorial RD

http://slidepdf.com/reader/full/tutorial-rd 1/34

Step 1

1) Make a sketch with a circle on the front plane.

This represents the pitch circle that defines 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.

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.

https://d2t1xqejof9utc.cloudfront.net/pictures/files/21219/large.jpg?1369003692



Step 3

3) Draw a vertical construction line through the

centre and a horizontal tangent to the circle. The

lines meet in the first point on the involute curve.

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.







Step 5

5) Draw a perpendicular construction line to the

pressure angle line through the centre.

Step 6

6) Draw a construction circle through the centre and

the point found in the previous step. 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:

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, thismeasurement will update to a new value.

Step 8







8) I hide the sketch relations in this step to remove

clutter from the images.

Step 9

9) I will now construct the “virtual” string when it is

“unwound” a little more. Draw a centerpoint arc as

indicated.

Step 10

10) Dimension it to a nice round number, e.g. 5. This

has to be an ARC DIMENSION. You click the two









12) Press = when the dimension modify box is open

to define an equation.

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.

Step 14

14) Click +







Step 15

15) Click the dimension of the “new piece of string”

(length 5 in my drawing).

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 is another 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”.

Step 17

17) Do a similar construction with an arc going the

opposite direction to obtain an additional point on

the involute.

Step 18

18) This time you subtract the arc length from the

original value. You can also draw a point offset the







initial value (13) along the base circle to get the

lowermost point on the involute.

Step 19

19) You can now draw the involute IN A NEW

SKATCH using the constructed points.

Step 20

20) Use the spline tool to draw a spline through the 3

or 4 constructed points.







Step 21

21) Press ESC to end.

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 numbers directly into the “Modify Dimension”

box as “=360/38/4”.







Step 23

23) Mirror the involute by ctrl-clicking the spline

and the centreline and choosing “Mirror Entities”.

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.







Step 25

25) When you look closely, you see that the involute

is a tiny bit too short to reach the outer contour.

This needs to be fixed.

Step 26

26) Go back to the first sketch and right-click it to

edit. Increase the length of the arc from 5 mm to say

5.5 mm. Due to the parametric nature of the







software, everything updates without you having to

do anything else.

Step 27

27) Return to the present sketch and verify that the

involutes now extend beyond the outer diameter.

Step 28

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

involutes.







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.

Step 30

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







Step 31

31) Mirror the profile.

Step 32

32) Draw the base (inner) circle.







Step 33

33) We are now ready to extrude the gear. Make a

new sketch on the front plane …

Step 34

34) … and choose “Convert Entities”







Step 35

35) Select the inner circle and click the green check

mark.

Step 36

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

gear wheel.







Step 37

37) Make a new sketch on the front plane, choose

“Convert Entities” again and check “Select chain”.

Step 38

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







Step 39

39) Do another extrude …

Step 40

40) … using the Up to surface and select the front

face of the gear.







Step 41

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

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 and click OK.









Step 45

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

visibility.

Step 46

46) Hide the sketches by selecting all and choosing

“Hide” (the glasses).







Step 47

47) Now comes the best part: Verification of the

design. Save and choose “Make Assembly from

Part”.

Step 48

48) Click the green checkmark for OK. This gives an

assembly with the gear wheel at the origin.







Step 49

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

the main window.

Step 50

50) Choose “View Temporary Axes” to show axes

for mating.







Step 51

51) Ctrl-select the two centre axes and click the mate

(paperclip) icon that pops-up.

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.







Step 53

53) Mate the temporary axis of the second gear to

the assembly top plane …

Step 54

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







Step 55

55) We are now almost ready, but the first gear is

fixed and can’t turn. Right-click on the first gear

wheel (the one with that has (f) in front of its name)

and choose “Float”.

Step 56







56) Now it can move everywhere so we need to fix it

so it can only rotate. Mate the temporary axis to the

assembly top plane …

Step 57

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

Step 58

58) … and the front plane to the assembly front

plane. Now both gear wheels can rotate

independently but they stay centered.







Step 59

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

mesh.

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.







Step 61

61) Right-click on the distance mate and change it

by a small amount …

Step 62

62) … e.g. from 76 to 76.1 mm. This gives a little

slack that’s necessary for the next steps to initiate.







Step 63

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

touch.

Step 64

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

top menu.







Step 65

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

Step 66

66) Click and drag one of the gears, and observe that

the other gear follows along and the involutes mesh

very nicely. You can go backwards and forwards.

This is SO COOL :-)







Step 67

67) We’re done. We have designed involute gears

and verified that they actually work according to

design intent.





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