I have made laundry soap using grated soap(ivory, fels naptha, etc) and it's a pain. Grating the soap takes a while and there's this yucky soap 'dust'. I've also done the whole 'melting' down the soap for a gel-like laundry soap. Also a pain. I also don't like the soap as much.
Skip it and use this recipe I've been using for over a year. Get a big bowl and scale up the recipe for a big batch if you like it. I only use 1/4 cup per load and it works fine. Add more if you want.
It's a bit messy but it's kinda fun plus if you make a big batch it'll last you for months. Go ahead, get your hands dirty!(clean??)
1 cup Vinegar (white)
1 cup Baking Soda
1 cup Washing Soda
1/4 cup liquid castile soap(like Dr. Bronners)
■Pour the liquid soap into the bowl first, stir in the washing soda, then baking soda, then added the vinegar in small batches at a time (the recipe foams up at first). The mixture is a thick paste at first that will break down into a heavy powdered detergent, just keep stirring. There may be some hard lumps, try to break them down when stirring (it really helps to make sure the baking soda isn’t clumpy when first adding).
■Mix well and store in sealed container.