I just ran the entire scenario as a test ( been a while since I did seps ). When you have split the channels, you now have 4 grayscale image files C-M-Y-K. When you convert from Grayscale to Bitmap ( Mode > Bitmap ), you will be met with the conversion dialog where it asks you for resolution. Set the bitmap resolution to 2400. This is the minimum amount of resolution needed to generate the dot in the screen. Also, in the next dialog, you set the frequency, angle, and dot shape. The frequency is default 53 lines per inch. Depending on the mesh of the silk screen, your frequency could be as low as 35 lines per inch. That's why I told you to contact a screen printer and ask them 1.) the mesh of their silk screen, 2.) the shirt fabric count and sewing angle ( if available ), and 3.) typical screen angles for a process color job. A good shop will give you that information because they rather not have to deal with separations if possible. But, the key is the Bitmap resolution has to be high enough to generate a good, halftone dot. I tried generating a sep at 5080dpi, but Photoshop wouldn't do it without distorting the image. A good halftone film positive depends on at least 5080 dpi; Photoshop only goes up to 2400 dpi.
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