banding in halftones

we get them sometimes. what can we do to be more consistant

we are printing at 45 degrees. the printer is a xante screenwriter 3. lpi is 32 to 45 on 1200 dpi. does this help?

I'll try the 5 , thanks. I can't see it on paper but I can't see it on velum until I burn it and it's in the screen