Using AutoCAD to reproduce irregular material arc edges

Usually the author of the layout is done in the rectangular steel plate, but sometimes will also encounter only a small amount of the layout of the situation, when the use of four meters of the entire plate will be the boss scold, how to do? Go to the workshop to find scraps ... Found the scrap and have the difficulty, irregular steel plate in the CAD show it? Look at this steel plate for the following shape (pictured).

But with only a tape measure handy, how can you get a curved side of it?

Whatever it is, make a few straight edges first and then, according to the tape measure, draw a few straight edges as follows:

But how do you determine the center of the remaining arc? This problem bothered the writer for half a day, from the workshop to the Office, from the office back to the workshop ran two times before the reaction came: why do we have to find this center, CAD in addition to the circle circle radius of the method, there are three ways to draw circles: tangent, tangent, radius method, two point (2P) method, three point (3P) method. Here with the three point (3P) method is not OK, and two of them have been identified, as long as you find a point on it. Remove the tape, from the right side of the steel plate to the left to take 200mm, Mark, in the mark to the vertical direction of the arc to the next straight edge of the distance of 173mm, good, back to CAD, do map. Use the offset command to offset the right straight edge to the left 200mm, the lower straight edge offset 173mm, extend the intersection of two lines: