Hi,
>> I'm not sure if a spline and polyline can be combined into a single polyline
Not to a polyline with just one command, but you can use command _JOIN to create a new Spline-object from your existing Spline+Polyline (a bit difficult with your geometry when you then try to close the open curve).
Alternative:
You can also try with command _SPLINEDIT to convert your Spline to a polyline, then run command _JOIN to join these 2 entities, make it closed an then extrude it. As shown here:
- alfred -
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Alfred NESWADBA
ISH-Solutions GmbH / Ingenieur Studio HOLLAUS
www.ish-solutions.at ...
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CDay 2026------------------------------------------------------------------------------------
(not an Autodesk consultant)