The legs were loose on this awesome painted stool, so I set about fixing them. In this case all that was needed was to tighten the hex bolts holding the legs on, but I had to re-set one of them, and in the process I dropped the fastener that anchors the bolt into the leg.
I dropped it in the somewhat cluttered laundry room of my house where I also have a small workspace. This room is no more than 8'x8', yet even after I carefully searched through everything in the drop zone (cleaning the room as I went) and checked behind and under the workbench, furnace, washer, and dryer, it was no where to be found. My best guess is that it rolled too close to the dryer and got sucked through the missing sock wormhole. This thing had simply winked out of existence.
I had no idea what this part was called, or where I could find another one. I could probably hunt one down at the hardware store, but why buy one when I could make it from scratch and had MakeIt Labs (complete with its machining tools) and a half hour of free time at my disposal?
To get started, I unscrewed another leg, being extra careful not to drop anything this time, and took it along with the bolt and fastener to the shop.
The fastener is simply a metal rod with a threaded hole drilled through the side and a slot on one end to align it in the stool leg. I measured the diameter of the fastener with a set of calipers and found it to be 3/8". I had a good hunch we'd have at least one 3/8" bolt laying around, so I went to the big blue bucket of bolts and dug around a little.
In a few seconds I had a perfect match:
The only portion of the 3/8" bolt I cared about was the smooth, unthreaded shaft. This was the stock material I planned to use to make the new fastener. In order to make the threaded hole I first had to drill out a rough opening, and then use a tap to cut the threads into the drilled opening.
I measured the bolt from the stool and found that the threading on it was 1/4"-20 NC. This means the the bolt was 1/4-inch in diameter with 20 National Coarse (a standard) threads per inch. I opened our tap and die set and grabbed the 1/4NC20 tap and the tap handle. According to this chart I'd need a #7 drill bit to make the hole I planned to tap, so I grabbed one of those too and headed over to the drill press.
I clamped the stock bolt into the vise at the drill press, put the bit in the drill, and centered it over the shaft of the bolt:
Then I squirted on some cutting fluid and slowly drilled the hole:
After cleaning off the shavings here's the result:
This would be good enough for what I needed to do, but at this point I decided to try and make my replacement fastener match the old one as much as possible. The old one had a taper leading from the surface to the hole, to help guide the leg bolt in. To add this I put a larger drill bit into the drill press and drilled slightly into each side, using the hole as a centering guide.
Now I was ready to tap the hole.
I left the bolt clamped in the vise, added a bit of cutting fluid, and slowly started to thread the tap into the hole. If it felt like it was binding at all, I'd back it out, clean away any cuttings, add more fluid, and re-thread. Eventually I could turn the tap smoothly the whole way through and the threads were done:
To test the threads, I took the bolt from the stool and screwed it into the freshly tapped hole. Perfect fit!:
Now I needed to get rid of the extra parts of the stock bolt. I used the old fastener as a rough guide to estimate the first cut, clamped the bolt in the small chop saw, and cut off one end:
Then I clamped it the other way, again using the old fastener as a guide, and cut off the other side:
The newly cut one is a bit longer than the old one, but this is fine since I planned to grind the ends a bit to smooth them out. To grind the ends I clamped the piece in the jaws of a hand drill and used it to hold the end at an angle to a bench grinder while I spun the piece with the drill.
This made a nice taper to the end
I flipped the piece around the other way and did the same thing to the other end. Here is the new one next to the old one. You can see it's still slightly longer, but since the tolerance in the stool leg is low it won't be an issue at all.
The last thing to add was a slot on one end of the piece. This slot is used to turn the fastener in the stool leg so that it will be aligned with the bolt. I did this by clamping the piece in a vise and cutting a shallow groove with a hacksaw.
Now all that was left was to reassemble the stool. Everything fit great and the stool is now as good as new!