"(PeteCresswell)" wrote in message
...
Per "PV" edrnouser@ spam telus.net:

http://www.ditchwitch.com/trenchless...s/compact/JT5/

The link above shows one type of machinery involved, Vermeer is another
manufacturer/

http://www.youtube.com/watch?v=GI-vVLJRZdg seems to show the
process.

Looks like I was off-base thinking that it could do curves.

I'm guessing that the operator keeps it level just by experience
and luck and that gray device that the helper is carrying along
as the bore progresses is just a sensor to tell where the bit is.
--
Pete Cresswell

No they can be steered.
The drill bit is assymetric.
When it is rotating as it advances it goes in a straight line.
To be steered off, it is hydraulically pushed while not rotating.
Due to being eccentric, it then goes off at an angle.
There is an electronic device inside the drill bit communicates it's
orientation so the direction can be determined