Setting up to run 3/4” minus on a 3 deck screen deck. Do I run just one 3/4 screen on top or will that wear my cross members underneath without screens on those?
Yes it will wear on the exposed parts how much might depend on your situation What is the feed material?
It’s a dirty pit lots of fines with clay.
Screens being installed is also part of the structure of the screen box when they are engineered.
Check to see if your crown bars still have a crown to them. If it’s a deck that you won’t be using for sizing/scalping, I just use “cheaper” 3-4” opening, 1/2” diameter woven wire screens and urethane crown bar strips. They work to keep the screen box tight and square. And they will last a long time. Depending on how much wear they have, just having a metal shop shear you the appropriate size of sheet steel and weld the new pieces to the side of the existing bars. It will help you tension the box and prevent it from breaking itself apart. I run Flexmat screens on the top and middle decks of my 5x16 and 6x16 gravel screens, and the mentioned oversized screens on the bottom deck.