This project can be done for very cheap - or not. A lot of the tools can be replaced with other items, as well as the parts for the stool. Also, if you don't have an old motorcycle saddle, you could use pretty much anything for a seat. Anything that you may want to sit on, that is.
Step 1: Tools and Materials you will need (and some you may want)
1. Miter saw - makes cutting the angled legs easier
2. Table saw (optional)
3. Drill with drill bits and a paddle bit
4. Angle grinder/cutter (I used this primarily for cutting)
5. Rotary tool (this I used to grind a smoother edge)
6. Impact driver (optional)
7. Random orbital disc sander (optional)
9. Sheet metal step bit
10. Wood glue
11. Tape measure
Materials I used
1. 1 of 8 foot long 4x4 - probably didn't need this much, as there was some scrap left over - six feet would probably be enough depending on the height you want the stool.
2. 8 of 4" lag bolts or construction screws
3. 1 stool swivel
4. Scrap wood - you will need a bit, but it doesn't have to look nice or anything.
5. 18"x24" Sheet of heavy gauge steel or aluminum; I used diamond plate aluminum, because it was thick and I like the way it looks
6. 4 of 2" sheet metal screws
7. 4 of 1 1/2" x 1/4" bolt or machine screw
8. Motorcycle seat (or whatever you plan to sit on)
(Optional for wheeled stools)
9. 16 of 2 inch sheet metal screws
10. 4 ball casters
Step 2: Plan it out and cut the legs
1. Find out what height you want to sit at. Find something to sit on that you like; I used a dining room chair because I don't like sitting up too high.
2. Use your tape measure to find out the straight line distance from the top of the chair (where ever you are sitting) to the floor.
3. Add together the height of your seat and stool swivel and subtract that number from the distance you measured in #2.
*****Now, you would probably be able to figure the length of your leg if you paid attention in geometry. Since I don't care much for congruence - here is the dumb guy way to figure it out.*****
4. Cut some scrap wood to the length you came up with in #3.
5. Set your miter saw to 15 degrees and cut off the end of a 4x4.
6. Set the 4x4 on the ground and line up your scrap, making a 15 degree angle.
7. Using another piece of scrap wood, line up the bottom of you first piece of scrap wood and the 4x4 and draw a line across the 4x4 (the diagram should make this more clear)
8. Cut off the 4x4 at the line using the miter saw
9. Repeat #6 - #8 until you have 4 stool legs.
10. If you want to clean up the look of the stool, use your table saw to cut 1/8" off of all four sides of the leg and then sand it. This will remove surface imperfections and make it look nice.
Step 3: Putting together the legs
1. Take some scrap wood and make four 15 degree wedges the same width as your stool legs. I glued together pieces of plywood to make mine.
2. Cut a piece of 4x4 to about 6" (if you used your table saw to cut off 1/8" from each side, do it to this piece too). This will be called the center piece.
3. Glue one of the wedges to the center piece and wait for it to dry. Do this until all wedges are glued in place.
4. Glue one leg onto one of the wedges, making sure it is lined up evenly. Wait for the glue to dry.
5. Use your drill with a paddle bit to start a hole for your lag bolt. Use an offset pattern so that the bolts won't run into each other when all the legs are attached.
6. Drill into center of the holes you just bored so that your lag bolts can go in easily.
7. Use your impact driver to drive the lag bolts all the way in.
8. Repeat #4 - #7 until all four legs are attached. The leg assembly of the stool should be able to support your weight now. You can test it for evenness by sitting on it and rocking around in a circle.
Step 4: Making the seat bracket
1. Place your diamond plate aluminum face down on the floor.
2. Place your stool legs upside down on top of the aluminum and trace around them with a marker. You should be left with something that looks like a Swiss cross.
3. Cut this shape out with the angle grinder. Smooth out the edges with the rotary tool.
4. Place the cross shape on top of your stool legs and place the stool swivel on top of the cross shape.
5. Using your marker, trace the screw holes in the swivel on the cross shape.
6. Use your step bit to drill holes big enough to accommodate the sheet metal screws through the cross shape.
*****Back to the stuff you need to do*****
7. Use your impact driver and 4 of the sheet metal screws to attach the swivel to the stool legs.
Step 5: Making the seat bracket
1. Remove all the hardware from the seat and trace the small bracket onto the sheet aluminum. Cut it to fit as needed.
2. Trace the seat shape onto the aluminum and cut it out.
3. Smooth out the edges with your rotary tool.
4. Place the swivel upside down and trace the holes onto the aluminum
5. Drill out the holes.
6. Attach the seat bracket to the swivel using your bolts.
Step 6: Attaching the seat and finishing up
If you want, you can add the casters to the bottom of each leg and attach with 4 sheet metal screws each. Be careful if you lean back, the angle may not be wide enough and you could tip over. This should not be a problem if the stool is tall enough.