Whenever you use power tools or machines, you need safety equipment. Since you will be creating a lot of sparks using the metal chop saw, you need to wear a full face shield, long sleeves and work gloves. It is always a good idea to know what you are going to cut and to what size. As a guide, you can do a full scale drawing with the exact dimensions and angles for all the parts of the chair frame. That way when you cut and grind them, you can take them and hold them against the drawing to make sure they are right.
Set the metal cutting chop saw to a 45-degree angle to cut the pieces for the back legs (Image 1). Check the cut piece against the full scale layout making sure it is the right length and has the proper angle (Image 2). Repeat this process, checking each piece for the chair frame against the full-scale layout. The long pieces should always be cut first. That way all of the short pieces can be taken from the cut off.