Transform a cheap shop stool into a safe wobble stool for your kid or your classroom.

You'll need:

Pneumatic Shop Stool (or similar)
Foam Pool Noodle (mine was 4'6" and just the right size for my stool)
Superglue/Cyanoacrylate
Utility knife
Hex wrench

Optional:

Spray activator for cyanoacrylate
Duct tape

Step 1: Removing the Wheels

Because I didn't want my 3rd graders zipping around the engineering lab on rolling stools, my first step was to take the wheels off the bottoms of the shop stools. The Harbor Freight Stools come disassembled except for the wheels, which were fastened with a pneumatic driver, so it was difficult to undo some of the bolts. I didn't have the right size wrench and ended up using pliers. I recommend a wrench.

Step 2: Slicing the Foam Noodle

You want a slit in the foam noodle that goes through one side, into the center, but NOT through the other side. The cut should go long ways down the long side of the noodle. When you're done, the foam noodle should still look like a complete tube, just with a slit down one side.

Step 3: Wrap the Perimeter of the Base of the Stool

Insert the edge of the base of the stool into the slit you just made, and continue wrapping it all around the edge.

Mark the end and cut off any extra to make a smooth join.

Press the edge together to make a complete circle.

Step 4: Glue

Safety note: Use proper ventilation, especially with spray activator.

Disclaimer: There probably is a better adhesive for this. Feel free to leave your recommendations in the comments. thistothat.com didn't list "pool noodle" as an option.

I adhered the pool noodle with cyanoacrylate/superglue (CA). It didn't work that well at first until I tried a spray activator, mainly because I didn't have the patience to apply pressure for two minutes to get a good bond. I applied CA to the seam between the foam noodle and the metal tray. I would apply glue to one section, then spray activator, and apply pressure for about 30 seconds. Sometimes I could see visible vapors and feel the pool noodle getting warm. USE GOOD VENTILATION. After 30 seconds the bond was pretty tight and I could move to the next section. I made sure to apply glue to both the top and the bottom edges. I also applied glue to the ends of the noodle, gluing one end to the other to hold the shape of the circle.

Step 5: Assemble the Stool

Put the stool together.

No problem. This type of shop stool doesn't even have any screws to tighten. (So don't let your students pick it up by the seat, or it'll fall apart.)

Step 6: Done!

Now, the harder part is training your students to use them safely.

These stools are easy for them to raise, but it actually takes more weight than most young students have to lower them again, so you will likely need to help. They can slide them, but remind them not to pick the stool up by the seat, since this kind of shop stool simply pulls apart. The foam pool noodle gives them a slight amount of wobble, but not enough to tip the stool, and it keeps them from scratching the floor, but I know it's not a durable solution. Covering the noodles with brightly colored duct tape would probably improve matters.

Have fun!