I was using 2 double cut files which were attached to angle iron using magnets. The magnets allow me to remove them and clean them regularly.
The setup worked but the shafts would ride up and down, so I recently switched the setup to one file and a wood guide with a 1/4 circle routered into the base of it. The 1/4 circle is 3/8" diameter. When pushing the shaft into the file, rotate it so that the shaft is rotating upwards into the file (i.e. clockwise if your file is on the left, counter-clockwise if your file is on the right). The friction of the shaft against one file will keep it firmly on the base and consistent with the space between the magnet and the base of the wood guide.
Using files it only takes 30 seconds going slowly, so I see no reason to use rasps.