LINES_ONLY Mode

 
linesgif
Using the drawing pen draw a shape.
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Press K.

Expand the menu from the bottom left corner of the screen. If you are adding to the overall geometry Select "ADD"(Union).

Menu slice
Select "Lines Only" option.
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This will create a mesh object using only the contours of the shape you have drawn.

Lines1a
Adjust the "Line_Thickness" to change the thickness. (In newer versions this is found under "Lines_Only" tab.
lines2a
Increase the "Smooth" slider to make the profile smoother, less jagged.
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Decrease the "Simplification" to increase the resolution.
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Increase the "Simplification" for a lower resolution.
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For an evenly distributed edges choose "Even Spacing ".
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Choose "Cubic Lines" option for a cubic cross section (or "Custom" if you have drawn a custom profile).
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Select "Taper".
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This will add a new curve object named "Taper_Curve".
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Select "Flip_Direction" to flip the taper effect.
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CUSTOM PROFILE
With the "Profile" material selected draw the shape that will be the bevel shape for your line.
custom prof
CUSTOM TAPER
Using the "Taper" material draw the shape to taper your line.
custom taper
CURVE OBJECTS
Turn on "Curves" button to keep your lines as curve objects.
curves