Date: 14 Jun 2005 14:39:51 GMT
From: Dave Hinz <>
Subject: Re: Extracting Recessed Bolt (Broken, Too!)

On Mon, 13 Jun 2005 21:37:53 +0000 (UTC), Craig's Saab C900 Site <> wrote: > Dave Hinz <> writes: > >>Penetrating oil, and then a left-handed drill bit, would be how I'd >>start. Have you tried swearing rather a lot? That sometimes helps. > > By left-handed drill, do you mean a drill bit which is designed to cut in > the opposite direction of rotation to a convention drill bit? Yup. It adds heat, makes a hole, and rotates the fastener in the direction you want it to turn on the off chance that the heat and torque loosen it up. > What is the > aim of drilling out the broken fastener? I presume if the correct drill size > is used enough of the fastener can be removed that the small bit left > engaging the thread of the original hole can be easily removed? Well, there are several approaches for a stuck fastener. The key is to preserve options, and to do that it's imperitive that the hole be drilled in the exact center of the stuck fastener. First, drill with the left hand drill bit, of a diameter of the appropriate easy-out tool for the fastener you're trying to remove. If you're lucky, the heat, torque, and kroil that you've put on to soak will act together and it'll come out. If you're less lucky, then you can use the ez-out which is kind of a left-twist, tapered corkscrew kind of a deal. It wedges into the hole & digs in, hopefully bringing the fastener out with it. When that doesn't work, enlarge the hole you started, and gummed up a bit with the ez-out, to the minor diameter of the bolt, or as close as you can get to it given how far you missed the centerline. In an ideal world, you'll hit it dead-nuts, and drill out everything but the long spiral of threads, which can then be removed with a pick or similar pointy tool. That never happens, but you can usually get it close. Again, left-hand drill bits help unless it's a through-hole, and then you can just thread it further in by drilling if it moves. When _that_ doesn't work, then drill it for the minor diameter of the next larger rated fastener, re-tap the hole, and use an M12 instead of an M10, or whatever. Not always an option, though. In any case, liberal use of good penetrating oil, and/or heat, and/or swearing, often helps. Dave Hinz

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