I have a hollow core tabletop, which is too wide for where it will go. I'd like to cut it into two pieces. What is a good way to finish the cut edge? Or is it just easier not to bother and get a better fitting desk?
As in the comment, a hollow core door has wood around the edges, and the center contains a cardboard spacer in a honeycomb pattern. When I shorten such a door, I cut it to the desired size, then take the cutoff piece, cut the solid edge part to fit, remove the veneer, and glue it back into the cut and exposed side.
don't worry about the bottom side. trim it to width, ripping off, say, 2". then cut through the bottom of top just shy of the top finished layer, essentially rabbeting the edge and leaving only the top layer. clean the bottom of the top layer, then glue the ripping to the top layer. this edge will be thicker than the other edges by the thickness of the top layer.
One option is to add finish trim around all four sides of the cut pieces. You could make a rectangle the size of the the table perimeter (e.g. from 1x2), and then glue it to the three uncut sides of the table.
(1) A crazy alternative would be to saw out a piece down the middle and put it back together. See videos on how to cut laminate counter-top for ideas and methods (masking tape, countertop jigsaw bit or fine-tooth circular saw blade). Various methods are possible to rejoin the halves. Best would be biscuit joints (but you need a specialized tool). A similar idea is to drill holes and insert wood dowels. In both cases use wood glue. Finally, toggle bolts can be used (again, look for videos on how to mate two pieces of kitchen countertop). In all cases, you can add metal straps on the underside of the table and (assuming it has one), the frame running around beneath the table top.
(2) If you prefer a saner approach cut off the ends you might try to reclaim the laminate used on each end (before you saw it off) and glue it back onto the new surface. I say both ends so that the legs remain centered.
(3) Depending on how the table top is attached to the frame and legs you can get the same effect but avoid making two cuts by detaching the table top from the frame. Cut one end and repair as above, then re-attach centered on the frame. Many times the frame is attached to the table top by wood screws from the underside and the legs are attached to the frame so this is not that difficult.