Flattening a 2 x 4 Face for Glue-Up
I'm trying to flatten a couple of 2 x 4s so I can glue them up and use like 4 x 4 for a work bench I'm building. The problem is I spent like 2 hours on 4 of them, and honestly I feel like I made them even less flat than they started. Every time I think I have it, I put two of them together and there are huge gaps between them. I've tried using a straight edge and marking where the high spots are, but it's not helping very much. Any suggestions?
I'm using a No.4 plane on 35" pieces. I would have gotten a longer plane, but they were like at least three times the price anywhere I could find them.