I am frequently asked about recipes to make Soap Flake Laundry Powder starting with bar soaps like Ivory Bar Soap.
Here’s a great link (ignore the word “detergent” in the recipe titles, it’s just another example of how we use the terms “soap” and “detergent” interchangeably without thinking): Link
Another place to find recipes is on Recipezaar.com — as I point out on the web site, these too are entitled “detergent” recipes. Evaluate them by the list of ingredients, not the title.