Why won't my 3D polylines display a linetype?

3DPOLY's cannot contain arcs, display linetypes or show width or thickness.  However, you can assign a linetype style to a 3D polyline and it will retain the information.   Simply save the drawing, explode the 3D polylines before you plot (the LINES will display the linetype), then undo to restore the 3D polylines.

Why don't my splined polyline vertices go through the original vertices?

As you probably know, using the Spline option ofthe PEDIT command creates a splined polyline but the path of the spline does not run through the original control points. In contrast the spline created with the SPLINE command does run through thecontrol points and is the end result you want. Back on the negativeside the SPLINE command has an option to convert an existing polyline, but only one that has been splined. The converted spline is still not what you want.

So the best way with stock AutoCAD is to turn on the endpoint osnap,issue the SPLINE command and get starting picking points. ToolPac users will find Convert Polylines to Splines that will process a selection set of un-splined polylines and give you the results you want.

How can I draw a tangent line off an ARC within a polyline?

You may have noticed that when you go to the ARC mode within the PLINE command, the first and consectutive arcs are tangent to the previous segment.  To create a tangent line off the last segment, first press L for Line mode, then press a second L for Length.  Pick or enter a distance and the segement drawn will be tangent off the last arc.  Its the 2nd L that does the trick.

How can I convert R14 LightWeight Polylines back?

At the command prompt type CONVERTPOLY. This undocumented command built into AutoCAD R14 allows you to convert lightweight polylines to the old 'heavy' polylines, preserves arcs and polyline width. Some 'not so current' applications may require standard polylines.