Lets see your die filing machine

[f350ca]

I think Victor tools has them, but I've made them, or repurposed I should say. Grind the end of the file down to fit inside a 3/16 hole , drill a 3/16 hole in a 5/16 shaft and epoxy it in. Then chuck the file and turn down the shaft to 1/4. This sets the shank in line with the file. Rob's might have a bigger clamp arrangement though.