Starting the task of creating new blocks to function as tabs to facilitate cutting of the objects in the drawing from real-world material. I created a box to the left of my main drawing, with an eye to drawing the fillets from the bottoms of the two vertical lines of the box. With the "Draw Arc - Three Points" method, I kept getting an "Invalid Arc Data" error when I first clicked on either bottom corner of the box, then clicked on two more, lower points, along the path of what looked to me like a quarter-circular arc.
I finessed the problem by creating a rectangle _inside_ one of the larger obects and then building the first tab inside that rectangle, which gave no further problems. It was easier to draw the fillets with the "Center, Radius, Angles" arc-drawing function. Than I created a block out of the tab after deleting the the extraneous lines of the starting rectangle, etc.
Next, I'll make seven other tabs to cover all the compass directions.