If your combination includes SVALNÄS shelves, screw them into the uprights as well. I wouldn’t place heavy objects on the top shelves though. I would also recommend using the shallow shelves (5 7/8″ depth) and shorter uprights (36 5/8″ height) to build a lower combination to prevent any top-heavy tip over possibilities.
That’s my take on it. Maybe other readers with experience on the IKEA SVALNÄS system can shed some light on this.
Jules Yap started IKEAHackers.net in 2006 as a personal blog to showcase the most impressive IKEA hacks from all over the world. Since then, she has learned a lot more about power tools and DIY. Her site has helped thousands modify IKEA furniture with step-by-step tutorials, craft projects and home styling.