You are a hard-core ping-pong wizard. You apply copious spins to every shot. People are impressed with the seriousness of your regard for the sport that is table tennis.
Then you leave your paddle in the trunk of your car. The once soft and sticky rubber (that is so crucial to your game) melts into the foam betrayal of the case that was meant to protect it. You remove the rubber through razor blades and sandpaper + elbow grease. You order new rubbers from the internet and patiently wait, looking forward to the future schoolings you will give your colleagues.
Wait a minute... you curse, you realize your paddle is a bit warped now. This injustice prevents you from sleeping well. You cannot stand the thought that this once noble implement, the extension of your will and motor function, is not as perfect as it could be.
So, you resolve to bring it back to its former glory.
Step 1: How to Make a Not-flat Thing Flat
How do you make a non-flat thing flat? You can perhaps surround it with flatter things, hoping that they will persuade your non-flat thing to become a flat thing. You consider what kind of flat thing would need to exist to to make this happen. One option is to buy a ready-made flattening thing, such as the Yasaka Clicky Press. But, you don't want to wait to castrate yourself with such a thing, when you know you could make the same thing in like an hour with a trip to Home Depot.
The basic design is Flat thing + Flat thing. You remember that trees are a source of flat things, and you go find some cut trees. You choose oak, which is a nobler and stiffer flattenerer at like $9 for a couple of feet of 1"x8".
Step 2: Make the Flat Thing
Use your table tennis paddle as a template for the first flat thing. Bring a giant metal teeth-thing to the oak. Don't cut your paddle! Cut the oak instead. You decide it might be nice to leave some space on the sides so your bat will feel less naked.
Step 3: Make Another
Put the first flat thing on top of the rest of your oak. Cut another flat thing based on the edge of the first flat thing.
Step 4: Put Holes in the Flat Things
I don't know why I did this. My hand must have been guided by a higher power, compelled to draw circles on the flat things stacked on top of each other. I decided it might be nice to make the holes pretty straight, so that I could put some 1/4 - 3" bolt things in them.
Step 5: Make the Flat Things Flatter and Protect Them From the Scary World With Plastics
Why not spray some polyurethane on them? I sanded them down first, to get rid of the rough edges. It was pretty cool to watch them spin around for a while, actually.
Step 6: Drown the Bat in Scalding Water
This is the only proper way to make it suffer for its crooked insolence. Rub any kind of protective glue off the sides with a sandy thing. You really want to make sure the water chokes into every last persistent thread of its existence. You see those air bubbles? Cool fact: I think it takes like half an hour to make sure the deed is done.
(ironically, the water makes it more flexible and less stiff)
Step 7: Squish the Thing Flatter
It seemed like a good idea to protect the surfaces of the press parts from the water of the drowned bat with something. I decided to use aluminum foil. Put it all together and tighten it up quite a bit. I think you probably don't want it to be so tight that the press is less flat than the bat.
Leave it somewhere warm. If you have a hot summer day handy, use that. I used an oven that thanks to a pilot light remains pretty warm most of the time.
Wait a while.
Step 8: Done!
You pretty much have to wait for the water in the paddle to leave. Then it'll be good and straight and will stay that way.
As a fun bonus, you can use your new flattener apparatus to apply the rubbers later (with less pressure).