Blair makes a nice tool. That's what I use. The key I found that makes it a lot easier is to center punch the HELL outta the spot weld so the cutter will stay centered.
I honestly never used a center punch. What I did was hold the drill at a good speed (2/3 or full power) and slowly bring it closer to the surface I was drilling. This scored the surface and provided a good starting point so that the bit did not wander.
In hindsight, maybe a center punch would have sped up the process. Never needed it to cut out my floor though. Also, I HATE switching tools. Much better with just grabbing one tool and going to town.
I'll keep the punch in mind next time around for sure.
