Factorio Forums

When you pick up a tunnel entrance with pipette button (Q), it keeps the orientation of the original, as expected
When you pick up a tunnel exit with the pipette button, it will reverse the orientation (turning it into a tunnel entrance).

This means that if you move a tunnel exit of an existing tunnel, it will invert the movement direction of the tunnel, potentially causing a base to break down.

Thanks for the report. It is not possible to build an exit underground belt manually. You can only ever do it with a blueprint, or as part of the paired entrance.

Diadem wrote: Mon Nov 25, 2024 2:19 pm This means that if you move a tunnel exit of an existing tunnel, it will invert the movement direction of the tunnel, potentially causing a base to break down.

This might explain some mysteriously-flipped undergrounds I regularly find in my spaghetti factories. But 99% of the time, the underground belt in your hand automatically switches to an exit when it detects that it will link to an existing entrance. If you can find a specific case where this does not happen, and the existing entrance is converted to an exit instead, you should make a separate bug report and include a save file that demonstrates it.