Drilling through floor

We've all done this: you get down into the unfinished basement, snake a few CATV or phone wires around the ductwork and pipes, then drill up through the subfloor into a pocket between two studs, and cut into the wall to put an electrical box for your new TV connection (or whatever).
But, how do you locate the hole, from below, so that it comes up in the right place?
I had several ideas, all bad.
(1) measure from the structural boards in the subfloor, accounting for 2x4 stud and other wall thickness. Isn't accurate if the house has brick veneer and I don't know the exterior wall construction.
(2) find a through-the-floor member and measure from that. Works in the kitchen, with drain or water pipes, but not across the house in a bedroom.
(3) drill a small pilot hole in an inconspicuous place and use that as a reference on both above-floor and below-floor measurements. Didn't have a long enough bit, at the time (can go a little over an inch with the small sizes - maybe I could've started with 1/8" and finished with a bit of clotheshanger wire?) I've drilled into the top of a 2x10 in previous attempts at this.
(4) put a magnet under the floor, and fish for it above with a pendulum. This one almost worked, but I was finding nails because the magnets were too short (ideally, want over 2" length between N and S poles for this kind of thing).
So, what DOES work?
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I did a "best guess" approximation, then put a .44 mag hardball through the floor. Perfect alignment. No drilling. No kidding.
nb
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I've never used one, but the local DIY store sells long, flexible drill shafts for this kind of thing (in the electrical section). You could run it in through the hole you cut for the box and drill through the floor from above... If you hit a joist, move over a few inches and try again. The first hole is completely hidden.
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I had one of those. I hit a joist, tried to keep going, and the drill got stuck. Couldn't move it down, or up, finally had to cut the shaft and leave it inside the wall.l There was some junk in the cavity, it fell into the hole and cemented into a blockage the back of the drill head couldn't pull past. And there wasn't any chip removal, so I couldn't drill through.
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Kind of overkill, a .357 or 9mm would have been adequate.
--
Better to be stuck up in a tree than tied to one.

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar.org
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notbob wrote:

LUVIT :)
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dadiOH
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whit3rd wrote:

1. Harbor freight sells 24 inch drills starting at 1/8 inch. So cheap they are disposable.
2. In an emergency (too lazy to go shopping) I have done this with a stiff piece of wire sharpened to a three-sided or 2 sided point. Doubt that coat hanger wire qualifies as stiff enough.
3. If drilling upward through carpet, have someone watch for it coming through. Carpet fibers can stick to and wrap around the bit unraveling a mess of carpet, especially berber. DAMHIKT.
--
Gerald Ross
Cochran, GA
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whit3rd wrote:

Determine where you want the outlet box in the living area. Use a piece of wire coat hanger chucked in a drill to drill a small hole in the floor along side the baseboard directly below the outlet box location. Leave the coat hanger in the hole just drilled and go into the basement to find where the coat hanger came through the floor. Drill up from the basement into the wall cavity using the coat hanger as a reference.
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Jack Novak
Buffalo, NY - USA
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wrote:

Look for where the other wires, pipes, whatever go through to the same place I want to go. It's kinda hard in this house though. It's on a slab. :-(
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get a 1" steel pipe, about 1' long, braze some cut/uncut carbide chips on the rim of one end and a 1/2" steel rod centered on the other. Chuck up into a Milwaukee 400 rpm 1/2" drill and have at it. Mine easily bored through 10" of concrete before snagging on a steel girder.
nb
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It's difficult to get to the bottom side of the slab, so one can drill up into the wall cavity, though. ;-)
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Sure, we've all done it.
My turn caused me to get an "installer's drill bit" - about 1/4 inch wide and some 15 inches long.
This just fit between the wall and my baseboard (after a bit of prying).
Just drilled a hole thru the floor into the basement (could be a crawl space) and left the drill in place. Went down under, added some wire/cable to the drill bit and backed the bit out drawing the wire with it.
Worked for me.
P D Q
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I have used the coathanger method many times. Cut the straight section out of the hanger, sharpen a flattened point on the end. Chuck in a drill and gently use it to drill down through the floor just in front of the baseboard and quarter-round if you have it. The hole is so small that you just put a little wood filler in it and no-one will find it even yourself. When drilled through, stop the drill so you don't hit any wires, and press the wire down as far as you can. Measure the distance from the wire to the wall surface. You can unchuck the drill. Go downstairs and look for the wire. Measure from where the wire protrudes. You add the space between the wall and the wire as measured upstairs, plus the plaster/drywall thickness, plus 1/2 the framing depth, and drill up at that point.
If you hit a joist going down move over and try again. It always worked for me.
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EXT wrote:

You have better luck than I do. Last time I did something like that it took me three tries to find a joist space that didn't have flatbar, hammer, or some other metal tool dropped down inside it.
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wrote:

Removing the wall trim at the floor drill a small hole through to the basement insert orange painted nail.
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"whit3rd" wrote:

You can't get there from here.
You can buy 1/8" x 6"-8" twist drills (Maybe longer) from a decent hardware store.
Simplest way is to drill down from the top penetrating the floor and projecting into the basement below.
You then have a point of reference to corectly locate where the hole needs to be and drill it from underneath using the projecting 1/8" drill as a starting point.
If you are lucky, you may be able to pry quarter round molding away from the wall to drill the 1/8" hole inside the foot print.
Worse case is you drill thru the floor in a visible place and have to come back and plug it with some colored filler.
Lew
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whit3rd wrote:

flexible drill. Instead of a coat hanger I use a sharpened bicycle spoke for the drill. It leaves such a small hole that it is usually not necessary to fill it. Earl Creel
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