Built a quick and dirty thumb.

[D2Cat]

Your welds look real good, but welding AR400 is like welding cast iron. Peeling that weld off doesn't surprise me, if you didn't heat the iron and cool it slowly.

 

[ovrszd]

Easier said than done working blindly.

After enough use you'll figure it out. There are times when I'll exert extreme forces on my Grapple but I recognize those times and am extremely cautious. Just remember the Grapple gives you the ability to put forces on your FEL that are impossible without it. So when you did this damage try to imagine where those forces came from and how much abusive force was applied to portions of your FEL frame in the process. It's a learning curve.