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na mara
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changing a bicycle sprocket size while maintaining shape,

Mar 28, 2012 12:39 PM


this is a stroke of a path of a bicycle sprocket with 32 teeth,

after removing 4 teeth from 4 different parts(there is a pair of 2 different type of teeth after every 6 standard teeth,i want to remove 1 of these 6 in each of the 4 parts)


I do not know how to join up the open ends of the path

to maintain the circular shape to produce a  28 tooth sprocket,

the teeth size are not to change just the circle,

thanks if anyone can help,


stroke path 32.jpg

  • Currently Being Moderated
    Mar 28, 2012 12:44 PM   in reply to na mara

    Select complete bicycle sprocket


    Go to object>path>join

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  • Currently Being Moderated
    Mar 28, 2012 1:44 PM   in reply to na mara

    You might make your life simpler by creating a pattern brush for the sprockets. Here's one approach. I'm sure there are numerous ways to do it.

    Screen shot 2012-03-28 at 3.41.55 PM.png

    Adjust the "Scale" setting, in the brush dialog, to get the right number of sprockets.

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    Mar 28, 2012 3:29 PM   in reply to na mara

    na mara,


    The shape/shapes of the individual teeth actually has/have to be changed to go from 32 to 28.


    You may maintain the concave rounded part forming the transition from tooth to tooth and their faces, but the transition/angle between the face and the top land (the tip) changes with the size, as does the shape of the top land itself, following the outer bounding circle which has a different size (28/32 of the original one). The inner bounding circle corresponding to the bottoms of the roundings also changes, of course.


    This means that you will have to create everything anew.


    You may do it in different ways.


    Using a Pattern Brush is one, but then you will have to know the angle/transition, so you will need the bounding circle.

    An Art Brush will adapt, with a certain change of shape when applied.

    In either case you will need to use a path that is a circle midway between the outer and inner bounding circles, and to make the two different teeth the right height (corresponding to (half) the difference between the bounding circles.


    A third way is to:


    1) Draw the bounding circles,

    2) Draw/redraw/copy one normal concave rounded shape vertically above the centre so its bottom touches the inner bounding circel and so that it is extended to cross the outer bounding circle (without the rounded transition to be made later),

    3) Rotate 2) round the centre by 360/28 degrees (you may rotate a copy),

    4) Repeat 2) for the different rounding (you may edit the original normal one if you rotate a copy in 3),

    5) Rotate copies of 3) round the centre by 360/28 degrees 5 times, now you have the basic shapes of the 6 normal roundings and one different one,

    6) Rotate copies of the whole set of 7 roundings by 90 degrees 3 times to have the full circle,

    7) Hide or delete the inner bounding circle, select everything, and Pathfinder>Minus Front, now you have all roundings/teeth, only without the rounded transitions,

    8) Use the free Round Any Corner script, either on all transitions at the same time or first on the normal transitions and then on the special ones (to get different roundings).


    The Round Any Corner script with instructions is available here:


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  • Currently Being Moderated
    Mar 31, 2012 3:04 PM   in reply to na mara

    This is the way i would do it admittedly irt requires working this the various setting until you get it right bu you can after some experience update the art fairly easy using the Transform effect.


    Screen Shot 2012-03-31 at 6.01.24 PM.png

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    Apr 1, 2012 9:23 PM   in reply to Wade_Zimmerman

    Wade, how would you make it a filled shape, using this method?

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    Apr 2, 2012 2:47 AM   in reply to rcraighead

    Object>Expand Appearance




    See the other thread (about "expanding a circle") to avoid fiddling around with settings.



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    Apr 2, 2012 3:38 AM   in reply to rcraighead



    And be aware that whenever you change the size of the defining circle, the angle between adjacent (later to be sub)paths will change, in other words you will have (possibly insignificant, depending on your requirements/inclination) small disruptions of the shape (change of direction where they meet or top lands that are straight (plane) instead of circular (cylindrical), unless you do it (corresponding to) the way described in post #3, where the paths cross the outer bounding circle and cut themselves out of it (with subsequent rounding, if needed).

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    Apr 2, 2012 5:31 AM   in reply to Jacob Bugge

    Using Transform Effect, there is no defining circle path to change the size of. The diameter of the sprocket is automatically determined by the widths and number of teeth, as it should be. Draw the original path symmetrically; from center of top land to center of the next top land. That will cause the angle change to occur at the center of each tooth point, rather than at the side of a tooth and the next bowl. In my experience, the tops of motorcycle sprockets do not describe a large circle; the teeth usually have tapered facets at their tops, so that there is not a sharp edge to encounter the chain rollers. But if you want that, it's easy to do after expanding the effect and joining: Just draw a large circle and use the intersect Pathfinder.


    Actually, the arc of the bowls on an actual sprocket may differ from 180° depending on diameter, too. But that's probably needless hair-splitting for illustration purposes.



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    Apr 2, 2012 6:13 AM   in reply to rcraighead

    Expan the Appearance and Command or Control J and fill it?


    Screen Shot 2012-04-02 at 9.08.16 AM.png

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