I have a closed path from which I would like to create a parallel inner path. If I drew a series of lines, all the same length, with one end at points along the path (all extending inward), the second path I want would be defined by all the other ends of the lines, except where the lines cross, in which case, the inner curve would be defined as shown in the example image. Does anyone know how I can efficiently create this path? I looked at blending, but couldn't get the lines to orient correctly. I don't mind doing some hand work. I just don't want to have to draw a huge number lines calculating the angle for each. (Drawing a path that follows the inner line ends would be easy if I could get the perpendicular lines.)

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If you only need the parallel inner path, you can use the Offset Path tool under Object->Path->Offset Path. You'll just need to enter a negative number as the offset value to make an inner path. The Joins and Miter Limit options work the same as the Corner and Limit options in the Stroke panel. Just make sure you have the Preview box checked to make sure it will look like you want it to. Note that this will probably add a few extra anchor points to the new path.

Offset Path tool

It's a little unclear if you actually need the small perpendicular lines or if you were just using them as a tool to make the inner path. If you do need them, the simplest way to make them is to add a Dashed Stroke to one of the paths. Just give the path a stroke equal to the value you used to create the offset path, set Align Stroke to either Outside or Inside (depending on which path you're using), and check Dashed Line. Then just adjust the Dash and Gap values until it looks like you want.

Dashed Stroke Settings

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The easiest methods I can think of are a Dashed Stroke or a Pattern Brush. Either would need to be expanded then corners or curves fixed manually, but both would certainly quickly fill most of the path with lines.

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