Not really a how-to, but I found that using ViaCAD 9, I could make a reasonable printable thread by first making a closed surface of the thread profile, then mating that up with a helix spline that was set up with the correct pitch and diameter I needed for the threads (in this case 3mm pitch and I think it was 14mm diameter). After that I used the one rail sweep solid tool to spin the thread profiles up the helix, and bam! I had threads. The only problem I had after that was finding the balance to make them usable on a printed part. My first test was was too tight to turn by hand. I ended up with a gap between the threads around 0.4-0.5mm (closer to 0.5mm) and that was able to work with a layer height of 0.15mm when printed. The thread profile in the pic does not reflect the final design since I had to tweak the threads with the push/pull tool to get the correct gap. Since I knew I was gonna have problems with the threads I printed some smaller test parts first to dial in the threads. Now just gotta print the part.
My mission is to lower the collective IQ of teh Internets one post at a time.