Here's what did work for me.
You'll need: plastic toothpicks, a drill with a very small bit (or something equivalent, you can do this with an X-Acto knife if you're patient), and a place you can drill through without hitting anything underneath. If it's buckling spring or rubber dome, you'll have a hollow stem you can go through, which will work just fine. If it's Cherry MX, you'll be forced to place your bump off center unless you can go right up the middle of the mount (probably possible, but you may need to modify these directions).
Start by drilling a hole through the key where you want your bump to end up, subject to the condition above (it has to be clear underneath). You can do this drilling from the top down or the bottom up, depending on the construction of your keys. This hole must be smaller than the maximum diameter of your plastic toothpick, but large enough that you can insert enough toothpick to get through the top of the key.
Second, insert your plastic toothpick into the hole. Assuming you used a drill bit and not a knife or something, you should have a nice cylindrical hole, which means the toothpick will wedge at the same point whether inserted from above or below. Take advantage of this fact, and insert it from above, then mark where it stops. You want to cut it a little bit longer than that, and have the extra diameter act like a screw or nail head. Then re-insert it from below. You'll have a pointy spike sticking out of the key. Carefully melt this, forming something like the plastic rivets that hold a Model M together. Once it cools, it will be too large to be pushed out from either the top or the bottom. Then file or shave it down to the size you want.
If you screw it up, trim off the rivet head and push the piece of toothpick out. Make another one. If you made the taper just big enough to be a friction fit, you may be able to force it through the hole from below. Or, just drill it out with an even tinier drill bit.
- rivet.jpg (229.13 KiB) Viewed 1259 times
If you can't get through the key where you want the bump, perhaps just a deep blind hole will do. Force-fit the toothpick chunk from the top, clip it off, and melt/file/shave it to shape. This could find its way back out if handled roughly, but that wouldn't be a huge disaster if you still had access to your donor plastic.
For donor plastic, I used Dentek Triple Clean flossers. They're nice and pointy and have a gentle taper appropriate to the task, and also melt relatively easily. They're also cheap and easy to find.
