I bought some 1" smurf tube so that I could run coax, ethernet, and speaker cable to various low voltage outlets in my house. I used a 1-1/4" speedbor bit to make a hole in the floor from my crawl space but discovered that the smurf tube was 1" inner diameter and 1-1/4" outer diameter. Oops. It turns out it is very difficult if not impossible to force the flex tube through the approximately 6" deep hole.
I tried using a file to widen the hole but it had little effect. Should I try widening the hole with a 1-3/8" auger bit, a 1-3/8" spade bit, a sanding drum bit, or something else? There's not a lot of room in the crawl space so I'm hoping to hit upon the solution the next time I go under.
Best Answer
Now you've learned the hard way, the same way the rest of us learned, why they say "measure twice."
A spade bit may work for this trick, but an auger bit may be easier to control. First, use the bit to cut a hole in center of some scrap wood. A piece of plywood that's 4"x6" would work well, and a 2x4 that's 6-8" long would also work. You need a few inches on each side of the hole, and enough so that it doesn't shatter apart when the drill bit is vibrating inside, but thickness isn't that important. Since you're working in a crawl space, start a few screws on each side of the hole that you drilled.
In the crawl space, line up the hole in the scrap wood with your existing hole and screw it into place so it doesn't move. This wood is now your guide to keep the drill bit from running all over the place. Put your drill bit inside this guide, make sure you're aligned, and drill your larger hole.