BamBam, I've been looking through what books I have here in my office and couldn't find a chart that has the specific dimensions of the cut backs you need. When I said I use the nominal pipe size as a cut back please remember to add the thread length that will be inserted into the fitting back to the the measurement. It gets confusing trying to explain the way I do it and my way could be completely wrong answer for your test. As B-wire stated that the machinists book says to tighten 1.5 turns where is I usually try to get 2 turns. I have a machinists handbook and they are very good sources of info. but not sure if it has the chart for fitting allowances. Through experience I have learned when possible to thread one end and make up the fitting before I measure so that I eliminate one variable before I layout the cut-line. I do this with welded pipe as well. I get better results measuring to center of a fitting on the end of a pipe and allow for only one fitting on the other end than I do trying to allow for both fittings. Sometimes you just can't do it this way but I find I have less mistakes when I can. You may find some good information on this website, I didn't have time to go through all of it but you might check it out. I'll keep looking when I have more time and good luck with your test!
