Tutorial how to make synchronous belt

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Step 1:
firstly open a sketch to front plane and draw sketch like this
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Step 2:
use trim command
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Step 3:
use circular pattern command
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Step 4:
connect the circles and use circular pattern command again
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Step 5:
and extrude the sketch
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Step 6:
open a sketch side of part and draw 2 circles
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Step 7:
extrude it
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Step 8:
go back side, open a sketch. close the back side with extrude
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Step 9:
use fillet command
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Step 10:
you can add a thing like this
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Step 11:
all done:)) your synchronous belt is ready. very simple