I am trying to cut a slit through a plate at a 45 degree angle to the flat surface. I have been unable to draw a guide line on the edge of the plate.
Did you try adding an additional sketch with a line that is at the 45 degrees you want and using it in the "direction of extrusion" box? Here's a screen shot:
I've attached my quick model for you to check out too. Hope this helps.
You can also select one edge and the top surface to insert a plane at a 45 degree angle the cut extrude through both ways
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