Take a sturdy screwdriver of good quality. Heat with a torch (or print picture and instructions and have your local welder do it for you) and make the right angle bend. Quench to re-harden. Grind the inside corner of the blade so it has sharp edges. You will need a slightly negative rake so it stays at the bottom of the groove as you drag it and this can be accomplished by holding the handle up a bit (which you do anyhow to protect your knuckles). So that the slightly raised handle does not lift the working point, grind the aft end of the blade up at a slight angle as can be seen in the picture.