Hi folks. I work as an AutoCAD drafter for a wastewater/water engineering company. I use a manual, the American Pipe Manual to help me draw different types of pipe fittings. When I come to the 90 degree reducing bends, the only information I get is the center radius of the bend. Example: 6"x 4", 90 degree reducing bend has a center radius of 6". But the manual does not give inner and outer radii. So my question is, how do pipe engineers figure out what the radii will be for the inner and outer radii before the casting process. Are there equations to figure out the inner and outer radii, if only given information of the center radius? I'll attach a *.bmp file so you can see an example of what I'm trying to draw.