Why don’t they just retract the bits and change them like I would on a regular drill that needs a new bit?
Is the failure mode they always or often fall off the shank into the hole and they can’t be extracted?
Is the failure mode they always or often fall off the shank into the hole and they can’t be extracted?
Which suggests just leaving the old drill bit somewhere in the ground. But currently doing that would also involve removing the pipe, as to why: https://news.ycombinator.com/item?id=43371776
The actual way to avoid the problem is by using bits whose design lifetime in the formation you're drilling is at least as long as the hole section you're planning to drill.