THE BIG THING: I don't want to disassemble it, so I hope these photos help in the explanations below.
The Cardboard Scratchin Pad...
1. Build a small frame of 1" x 2" wood. Mine is 12" long sides and 8" long ends. The corners are just butt glued and a single screw in each corner. The size isn't critical, but make the frame first.
2. Use the frame to cut a piece of corrugated cardboard the same outside size (use the wood frame as a template).
3. Use the frame to cut a piece of plywood the same outside size.
4. Cut 2" corrugated cardboard strips the lenth of the long inside dimension of the wood frame. Mine takes 22 strips to fit tightly, but it will vary depending of the cardboard. This will keep the top of the cardboard strips a little higher than the wood frame.
5. Pack the cardboard strips into the wood frame as tight as you can. Then, with a hand on the cardboard strips, lift the wood frame up a little (like a 1/4").
6. Turn it over and cover the bottoms of the cardboard strips with yellow glue (like Elmers). Spread it smooth (a extra piece of cardboard is good for that). Note that the wood frame is NOT covered with glue.
7. Turn the whole thing right side up and set it on the cardboard base. Leave it overnight. The cardboard strips are now ONLY glued to the cardboard base.
8. The next day, push the wood frame down to the cardboard base. Turn the whole thing bottom side up and screw the plywood bottom to the wood frame.
9. Here's the cool part. You now have a refillable corrugated cardboard holder. The cardboard strips are only glued to the cardboard bottom and the plywood holds the carboard bottom to the wood frame.
7. To refill it when the cats claw the cardboard strips to pieces (which I am guessing will take at least 6 months), all you have to do is unscrew the plywood base, slide the wood frame off and go back to step 4!
8. Since mine is on a wood floor, I glued rubber mesh shelf liner to the cardboard bottom. That makes it not slide around. Double sided carpet tape would work well too. Don't cover the screws though, or you won't be able to remove the plywood easily.
I'll be glad to add any details I left out if there are questions...