I second the hesitation to drilling holes in the frame.

For one the down tube is under tension just by sitting on the bike. Then it is further under cyclical torsion with every pedal stroke. Then following that, the tapped threads are sharp leading to stress concentration. Considering the actual hole size is the most extreme distance from edge to edge inside the bolt threads inside the bore. That makes the hole quite a bit bigger structurally than it appears by eye or the drill bit you used.

Red flags all over the place on this one.

Good cool wet rags, moderate heat, a bit of silver & a post in the frame builders forum for some advice ftom the real talented builders there are all things I suggest.


Fwiw: Why not a real spot weld instead of JB Weld?