I wanted a LACK shelf to fit a space in my hallway that was 170cm wide but the nearest size was 190cm. My plan was to remove the end cap from the shelf, cut the shelf to size and then to reattach the end cap. This is the approach that I took:
1. I decided to shorten the end of the shelf that was going to be least visible.
2. The first step was to remove the chipboard block. Other guides about disassembling IKEA products mentioned using heat, so I used a hairdryer to heat the area and then a chisel to pry the block out.
3. I clamped a straight piece of wood along the edge of the end cap and used a utility knife to cut the edge. I managed to pry the top of the end cap away from the shelf, but it became too difficult to work with the rest of the shelf in the way. So I used a saw to cut the end cap off the shelf.
4. With the end cap cut away from the shelf, I was then able to use heat and a chisel to remove the outer edges from the end cap.
5. I cut the shelf to the desired length. I cut a notch out of the rear chipboard strip on the shelf with the plunge blade attachment of a multipurpose saw tool to allow the end cap to fit. I also cut away some of the interior cardboard structure to allow the end cap to fit.
6. I replaced the end cap and glued back in the chipboard block. I used some white caulk to clean up the edges around the end cap.