Depending on the type of surface you're dealing with I've had good luck with a cup Peroxide, 1/4 cup of baking soda and a tiny bit of liquid hand soap.
The original directions were to put it in a spray bottle and spray it on then let it dry, then wipe it off with a clean wet (not dripping) cloth.
I prefer to liberally wet (not dripping) a rag and wipe it down. I would do this on one of the Singers with the baked enamel finishes (The 401/500/301 etc) for instance, I would think a plastic machine would be OK too. Don't do it to a shellac finished machine though (ie one of the old Black Singers - other than the 301)
The gotcha is you must be very careful that it doesn't get on anything that is unpainted metal. It won't damage it other than introducing moisture, which is bad.
I did this to rid a machine of cat urine and a few machines that reaked of cigarette smoke and not just the nicotine type.