I made my own tool. But the process is the same. And it can be tedious at first. I would start by taking the first cut about 1/3 as deep as the stock valve relief. And mesaure how much clearance you have. Repeat as necessary. I used a collet as a depth stop. Your tool should have came with one. Once you figure out how deep you need to go on the first piston. Use the collet and some feeler gauges to set the depth for the rest of your cuts.
Number one most important thing is to Tape the hell out of the area around the piston, if not, all the shaving's will go in the engine.
Also do NOT put a cordless drill on the tool, while it first glance it would appear you do, I assure you, a couple turns takes out quite a bit of material and in all likelihood you don't need to remove much.
Me personally I would not do it again, I would plan better.