Making a top opening litter box

I recently purchased a top opening litterbox. I love the design and ease but I think it is too small for my American Shorthair. Has anyone made one of these from a large rubbermaid type box? If so, how do you cut the opening in the top so that the plastic is not rough but it is smooth around the opening? Thanks

I have never done this but here is a suggestion. Use a file to dull the edges and for extra protection use duck tape to cover the edge.

I know I read on here not long ago of someone doing this, but without the search feature right now, I can't find it... hopefully they'll see this post and chime in!

You could use the duck tape or possibly use a wood burning tool to smooth the edges. (Probably will stink when you are doing it, so i` would`nt do it in the house)
Linda

I'd look at melting the edges too. A wood buring kit is a good idea. Seems to me that duct tape is just asking to get the litter stuck and messy.
What about getting a clear flexable hose (like the kind they use to connect fish accessories) and cutting a slit down the center lengthwise then slipping it over the rough edge? You could cut it to fit easily, it'd be smooth and easily removable for cleaning. You'd just have to cut the hole a tad bigger to allow for the edge of the hose. It might actually work! And I got to use the Einstein emoticon!
Much luck

I think I remember reading on here somewhere about gluing a type of carpet onto the top, wrapping the edges into the hole. This way your cat has another place to scratch, the edges are smooth, and the carpet will help catch what litter sticks to kitty's feet on the way out!