We use an auger bit 1 1/4 - 1 3/8 and the more solid extenions, I think they are 3/8". I like the kind with noches in the shaft where it couples to the next one to keep it from comming apart. Nothing worse then when your set up comes apart in the cieling. Oh ya, there is. If you drill thru the next floor or roof. Had some close calls. You want to drill as harizontal as possable. If your allready working from a hole cut in the cieling like a 6" can cut out you can't drill strait. It drills at an angle up. That will limit you to 3-4 joists. You can drill the same from the other side. Try to drill strait tward your target or it will make fishing harder.
Your not going to make 12' unless you have a large open space into the side of the joists like a garage or utility room. About 6' in the middle you will be short. I would just notch the bottom of the joist and drywall/plaster about 1" wide by 6". It' does not take much. Just enough for the wip and a strap to be under the finished cieling.
Some bit work better then others. I like the orignal auger cause it seems to cut on reverse. So it wount get stuck as easy. Sharp bits will help. If the angle drill gets too close to the drywall put a piece of cardboard between it. This will keep you from marking the cieling.
Try to listen and get a feel for what your drilling. If it takes too long to go thru you might be cutting into the prywood upstairs (too high). Any noise for contact with a pipe. Does not hurt to pull it out and check with a flashlight. Go upstairs and look to see where a bathroom is to warn you where pipes should be.
Maybe someone elce can do better with those deversabits but I don't like them.
Tom
