I just thought I should post a picture of a little used device nowadays that is designed for filing in a lathe. Obviously it is known as a filing Jig but the down side is that they are not commercially manufactured so cannot be purchased you will have to make it if you want one. It is fitted to the cross or top slide of a lathe and the file runs on the two rollers which have a stop step enabling the file to be located in the same position every time. It is height adjustable so you can file a flat on any round item held in the lathes chuck. And if the chuck is indexed you can file any number of flats on a round bar without removing it from the chuck and also bypassing the need to set it up in another machine to shape it when making a one off and with a shim placed under one side you can produce a flat that tapers.
It is archaic and half a century old now but worth its weight in gold if you want to produce a tapering four sided punch quickly.
Sometimes I feel the world is slowly haemorrhaging small clever devices like this as each generation slips off their mortal coil. I can see my sons looking at it and wondering what it is when I have left this world, and not knowing throw it away!!!!
