How to remove a Shimano SF-1200 or similar single speed freewheel

[John Doe]

For anyone who is stuck trying to safely remove a Shimano SF-1200 or
similar single speed freewheel, the kind with only two narrow notches.
Apparently there is a tool (TL-FW40) for removing Shimano SF-1200
freewheels, but here is a better removal tool. A makeshift freewheel
remover that works better than store-bought.

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 thin nail

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.