Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
for me the art determines the line count. Soft blends of pastel colors, faces, subtle tone changes appear better with a finer dot of 65-85 line or stochaistic. Bright contrasty art like Sports art, Super Bowl Rings, band art appear sharper and with more contrast in the 45 - 55 line range. Also cheap shirts = low line counts, finer tighter shirt faces or high singles construction = higher line counts. A 50 line count by a great separator and printer will look flawless, at 85 it would lose much of the details and high contrast.45 line- Athletic Art, cheap shirts, high contrast art.55 line - Good middle of the road - Sim Process, Band Shirts, Character Art65 line - Flesh tones, soft backgrounds, printing on white or lights. If dark, face of shirt needs to be tight to avoid dots falling in the valleys.85 line - high end concert shirts, extreme small details like faces in a band, or small tonal areas of design where a coarser halftone would only have a minimal number of dots.Stochastic Dots - Very small details, short tonal throughs, Index type of art over a halftone baseplate.
As to mesh count the formula is 3.5-5 x lpi. We sell 355 mesh to some textile printers.
I'm sure the math supports not using a 55lpi on lower than a 300 or so, BUT I have been using 55lpi on 225S recently with very good results. On a perfectly uniform fade you may notice issues at the high and low end, but I do a lot of color on top of color fades and small shadows, and a lot of uniform sized halftone fields on top of solid colors to lower my screen counts, even on spot jobs whenever possible, and there is a world of difference on how good the final print looks when I use 55 instead of 45 lpi. If I am losing a few percent, it far less noticeable than the difference in size of a 45 lpi dot and a 55 lpi dot.I have also started using SP1400 exclusively for any screens with halftones. It will hold dots MUCH better than the HVP I use for spot jobs, at the cost of longer exposure of course.
Dan, I think you misunderstand. It's not the mesh divided by, it's the line count multiplied by. Example. 55x3.5=192.5. So in theory a 55 line art can be held on a 196.