How to remove a Shimano SF-1200 freewheel.

For anyone who is stuck trying to remove a Shimano SF-1200 or similar single speed freewheel, the kind with only two narrow notches, and you want to safely remove it. Apparently there is a tool (TL-FW40) for removing it, but there is a cheaper and better way.

Requirements...
...a left side bottom bracket cup. I used one from a cheap looseball type that was replaced with a cartridge
...a rotary tool
...a nail (or something harder like a rivet)

How to make it...
...cut a slot in the cup, about 1/4 inch down through one side of the threads

That's all there is to it. The slot needs to be just thick enough so the nail can slide through it. No precision required, anybody who can use a rotary tool can do it. You probably have several attempts to get the cut right. Easy as pie.

Screw the cup into the Shimano SF-1200 freewheel so that you can see the slot almost disappear in either one of the freewheel's two notches. Stick the nail in there. Now that your cup is locked tight into the freewheel, use your cup removal key (like a Park Tool BBT-32C) to unscrew the freewheel.

If it breaks your freewheel, you get one more chance using the other side.