I just used my food processor to grate one bar of laundry soap, one bar of Sard wonder soap, 1 cup of borax, and 1 cup of washing soda. From my reading you don't need the Sard soap, but my kids are such grots I feel I need the extra stain removal powder. I made a batch up without it, and it washed okay, but didn't get the worst of Miss 1's shirts clean. This lot, with the extra soap, works brilliantly.
It doesn't suds up like store-bought powder, so it's fine to use in a front loader. You only need 2 teaspoons in a front loader, and 3 teaspoons in a top loader. This batch is going to last me ages. VERY economical.