Didn't fully count the beef on one side and pushed the bead in far enough away that there was no bevel so the metal was showing . No matter how hard I hit the clincher, it didn't do a professional job.
This is the only way to install metal corners, although plastic corners cannot be made. This allows you to quickly adjust the angle in about a minute. You just have to hit him hard to insert the teeth he produces. I used at least 4 nails, 2 on each end to hold them in place :)
Didn't work very well at first, didn't squeeze hard, sometimes the corner bar would bounce off. I've found that the clincher often gets stuck mid-shot and doesn't hit the bottom. By hand it looked like a burr so I machined the roughness until smoothed out, added a drop of oil and now it works great.