Let me add this, the pitted rust is small holes below the flat surface of the metal. The DA dos not obviously get into those pits. The wire cups helps get into those pits. You an also use some force with that wire cup. The ones I use are maybe 3 in. dia. Sandblasting gets the rust in those pits, but.....
There are always many ways to skin a cat, but some ways will work better than other. I have restored these old cars since the 80's. I have DA' ed rusted cars down to bare metal, used the best of PPG epoxy primers, and on rusted metal, Cars treated with t eh phosporic acid solution (Ospho) has had much better results pays later. But as time marches on, primers change and maybe get better ( or worse??)....... Rust a ***** and hates to die.
You are learning and it is fun. And as life moves along, you will find ways that work well for you.
There are always many ways to skin a cat, but some ways will work better than other. I have restored these old cars since the 80's. I have DA' ed rusted cars down to bare metal, used the best of PPG epoxy primers, and on rusted metal, Cars treated with t eh phosporic acid solution (Ospho) has had much better results pays later. But as time marches on, primers change and maybe get better ( or worse??)....... Rust a ***** and hates to die.
You are learning and it is fun. And as life moves along, you will find ways that work well for you.