Trimming Filleted Objects in AutoCAD
By default, all objects except circles, full ellipses, closed polylines, and splines are trimmed when filleted. You can use the Trim option to specify that filleted objects remain untrimmed.
To fillet without trimming
From the Modify menu, choose Fillet.
Enter t (Trim).
Enter n (No Trim).
Select the first line and then the second line.
The filleted object is untrimmed.
System variables […]
Source: CAD Blog.Net – Trimming Filleted Objects in AutoCAD
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