Posted by dellus on Mar 30, 2020; 10:34pm
URL: https://forum.librecad.org/Given-radius-circle-tangent-to-two-crossing-lines-tp5718627p5718637.html

Playing around a while following your recipe it seems to me that the matter of perfect and trimmable  tangents has nothing to do with using an extra construction layer. It seemed randomly whether the lines would trim both, one only or not at all. I found out that if you move a set of crossing lines with fillet to a different position it can behave differently on trim. So maybe a matter of coordinates values and calculation precision. Strange it always works when trim is on with the fillet command.

For the procedure to place a circle tangent to two crossing lines: it's not necessary to place the auxiliary fillet on an extra layer. Just use the crossing lines' layer and the draw the circle over the fillet. Then you can select the fillet only by pulling up a window around it and delete it.
Or, if it doesn't really have to be a circle by definition, modify the fillet via Properties to start and end angle of 0.