So, thanks for checking out this instructable; though to be fair it should probably be called a descriptable, since I'm going to describe how I made mine instead of instructing on how to make one of your own. I happened to have a great (for this project) donor stool, and that dictated all the styles and dimensions here; so this is only a guideline.

Materials List

donor stool
wood for base (2x4 and 2x3)
casters, 4 swivel
3/8 dowel
glue
screws
sandpaper
ballast point sculpin ale

Tool List

safety glasses
dust mask
table saw
circular saw
hand miter saw
miter box
pocket screw jig
belt sander
orbital sander
square chisel
drill
screw gun
mallet
clamps
pint glass

Step 1: Identify the Problem(s)

The first step with any project is to identify the problems that need solved.

My biggest stool issue (let's see you make a joke out of that) was the broken leg, fun house-style bar stool that has been broken and fixed a half dozen times. It never caused any injuries, but it did lead to some hilarities and a few scary moments.

My other issue was my old garage stool (aka homer bucket and piece of plywood) which didn't move at all, and tipped over really easily whenever my tool was 'juuuuuust over there'.

I decided I no longer needed the 'danger is my middle name' bar stool; and could really use a rolling, swiveling garage stool - thus a plan was born.

Step 2: Disassembly / Modification

The second step is disassembly.

I knew that I wanted to add some mobility to my garage stool, and that means swiveling casters. I happened to have an old set laying around, since I'm the kind of guy that saves everything; but if you are doing this and buying casters, get all swiveling casters, they're inexpensive enough at Harbor Freight.

Looking at my parts pile, I could easily see that I'd have to add a base to mount the casters to; I decided (based upon scraps laying around in the garage) to make a circular base out of a 2x4's and some 2x3's. I used a 2x4 to represent the base I would be building, set it and a caster on top of my pile of parts, and took a rough initial measurement (11-1/2").

I also measured my current garage stool (17") which seemed to be the right height when working, and applied some good old elementary math to determine that I'd need to cut the legs long enough to add 5-1/2" height to my parts pile. The legs mount to the wooden rings, which are each1-1/4" tall; the legs have a 1-1/4" long rabbet cut on each end, which fits into a dado on each ring. I cut the legs to 8"overall, and cut the rabbet on each end of my new short legs.

I then cut a series of 2x's to make the circular bottom base. I drilled pocket screws on the bottom side and glued and clamped them together to make a semi square edged base. Once dried and set, I placed the bottom ring on the top side of the base and traced the circle. Clamping the blank to the bench, and turning and re-clamping every few inches; I was able to cut the base using a circular saw, making dozens of tangential cuts. There is undoubtedly a better tool to use, but I don't own it. My scroll saw would take a week to cut through 2x's, and my jig saw would have burned itself up. With just a little patience, a face full of sawdust, and 5 minutes with a belt sander, I had a pretty round circle. I set the bottom ring on the base again, and marked the inside of the ring. I pulled the ring off, and drilled some holes for the screws used to mount the base.

Step 3: Sanding

Now is the time when we sand.

Sand everything. Inside and out. Then sand it again - a little finer. Then again. And again. And when you're finally finished sanding, come back to it and sand once more.

Sanding is super important, 95% of your finish appearance depends on your sanding. It's also tedious and extremely messy. Safety glasses aren't even a question, they're an absolute necessity. I'd recommend a painters mask also, especially when sanding finer than 150 grit. I spent hours sanding everything, and didn't want to bring a phone or camera into that sawdust cloud.

If you don't know the sanding process, there are some really good instructables on sanding; and a couple of brilliant tips, like:

Sanding Concave surfaces

Popsicle sanding sticks

Step 4: Reassembly

When it came time to put this all back together, I first had to ensure the previous problems of falling apart were solved. In its original form, the stool had bolts that ran through holes in the rings, and screwed into threaded sleeves pressed into the legs. The threaded sleeves would loosen over time, making for a wobbly stool. I needed a better design.

Since the rings already had large holes in them, I first thought of just drilling holes in the legs that would correspond with the holes in the rings, and use bolts, washers and nuts to hold them together. As I was describing this to a friend in the garage, over some beers (inspiration has to come from somewhere); he asked why I didn't just use dowels instead. The design changed immediately.

After clamping the rings and legs together, I drilled a pair of 3/8" holes at each joint; slightly enlarging the existing holes in the rings, and drilling completely new holes in the legs. I cut 16 pieces of 3/8" dowel to 3" long each, then chucked each cut dowel into my drill and gave them a quick sanding and chamfer at one end.

I put a dab of glue on each ring dado and corresponding leg rabbet, and put them together. Dowels were lightly swabbed with glue, inserted chamfer end first, and pounded into place with a mallet (a block of wood and hammer will also work nicely). The ring and leg assembly was then set aside to dry completely.

Step 5: Finishing

Once the ring and leg assembly was set, each dowel was cut flush; on both the outside of the leg and inside of the ring. Then the assembly was sanded again, this time as a whole. And again.

I then glued and screwed the base to the bottom ring, and stained them as a whole unit; along with the chair back, and set them aside to dry.

A full day later, the stain smell was gone, and I screwed the casters into the base (4 casters, 90 degrees apart, all bordering extreme outside edge of base), remounted the seat pad, and added the seat back.

Now to get back to work on that motorcycle.....