One way to scribe a parallel line around a workpiece is to trace the workpiece with a compass. But if the compass isn't held perpendicular to the edge of the workpiece or the points of the compass are set too close together, the scribe line may not end up parallel all the way around the workpiece, as you can see in detail 'a.'
The best way I've found to ensure a parallel line around a workpiece is to use a "posterboard scribe," like the one shown in the main drawing and detail 'b.' The scribe is just a small piece of posterboard with a hole punched in it for the tip of a pencil. Just punch or position the hole the distance you want the line from the workpiece.
By using posterboard instead of a compass, there's a much larger pivot point for making contact with the edge of the workpiece, which results in a more uniform line around the workpiece.
That would work great, except the line I need to make is toward the center, not the outside.
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