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Broken Bolt Extraction 2

Start with a tapered drill bit....
  [vote for,

Your typical screw-extractor system involves drilling an ordinary hole into the end of the broken bolt, and then jamming a special tapered tool into the hole. The tool grips the bolt and lets you turn it, to remove it.

It is not always effective, though. Some bolts are made of tougher stuff than others, and the special tool fails to grip properly, so it turns, while the bolt doesn't.

So, here is a better way.

The basic problem is that the just-drilled hole is cylindrical, while the special tool is tapered. The tool only interacts with the hole at one small area.

If the hole was tapered, also, though -- and it should be easy to make a drill bit that is tapered, which therefore makes a tapered hole -- then the special tool can grip almost the entire surface area of the hole. The broken bolt should then be easily rotated.

Vernon, Aug 18 2012

Pop Rivet Blind Drill Pop_20Rivet_20Blind_20Drill
Maybe suitable? [csea, Aug 18 2012]

Doomwatch http://www.imdb.com/title/tt0564476/
Series one, epiosode 1 [8th of 7, Aug 18 2012]

Reamers http://en.wikipedia...amer#Tapered_reamer
Widely known to exist, and be very useful. [8th of 7, Aug 19 2012]


       Straight- and Spiral-flute taper reamers are Baked and Widley Known To Exist.   

8th of 7, Aug 18 2012

       I doubt highly that this would improve the performance of an extractor at all, the ridges on the shank of the extractor are designed to establish maximum bite at about 1/4 turn in a straight hole, with the load placed as high up the increasing diameter of the tool as possible to maximize the strength of the shank. If the extractor was to bite nearer the bottom, rather than near the top, the amount of force that could be applied before the extractor broke would be reduced. If the extractor itself breaks you are faced with "a special problem", that of drilling out a clean hole with a piece of hardened tungsten in the middle, quite able to deflect your bit and ruin it's point many times over. No the system that we currently have is quite brilliant, and this new one seems to offer no improvement at all.
WcW, Aug 18 2012

       I have been told that the reason there are not large mountain ranges of rubber from tyre wear along highways is that rubber eating bacteria that live along said highways eat it all up. Similarly, bacteria is now commonly used in oil spills, gobbling up the crude in big unsanitary mouthfuls until it is gone, after which the bacteria drown, secure in the knowledge that 72 virgin bacteria will greet them in germ heaven. By now I should think the next logical step is obvious! It is simply to... er, you would just... oh dear. I lost me spot. Never mind...
Grogster, Aug 18 2012

       Be careful what you wish for ...   

8th of 7, Aug 18 2012

       [8th of 7], while I have seen "step drill" bits, I've never seen a smoothly tapered drill bit, that drills a tapered/conical hole. That's the basis of this Idea, which lets the user apply more force to the standard tapered screw extractor inserted into that hole, in the broken bolt.   

       Even if you can provide a link to some smoothly tapered drill bits, I doubt they are Widely Known To Exist. Most people don't need conical holes, after all!
Vernon, Aug 19 2012

       Anyone familiar with lathes, milling machines and drill presses will have come across both straight and taper reamers.   

8th of 7, Aug 19 2012

       OK, different terminology. I was thinking "drill bits" and you seemed to be describing something else. Certainly I've never seen tapered bits for ordinary hand drills, AND certainly I've never seen a "screw extractor kit" include any tapered bits to prepare the way for the special tools (tapered) that are forced into ordinary drill-holes.   

       So, just because both parts of this Idea may be widely known, the Idea itself, combining them, seems reasonably new/postable.   

       I will note WcW's comment about it being easier to break the extractor, if you can apply more force to it than ever before. All too often, though, what happens is the end of the bolt is expanded by driving the extractor tool into the ordinary just-drilled hole, making it even more difficult to get the broken bolt out.   

       If the extractor could fit into a tapered hole snugly, there would be less force trying to expand the diameter of the broken bolt. And remember that those special extractors are designed to be rotated in a certain direction to grip the bolt-hole; rotating them in the other direction loosens them. Unlike the "tapered pins" mentioned at the third link above, the extractor tools should come out of a tapered hole almost as easily as they would go in.
Vernon, Aug 19 2012

       // ordinary hand drills //   

       You mean all you have is an "ordinary hand drill" ?   

       Have you written your autobiography? If not, you should; it could be dramatised into a real box-office-hit tear-jerker for engineers, like Silent Running, or 2010 (although in the book, Dave Bowman does ask the Monolith Makers to" save the computer", so presumably HAL's consciousness survives).   

       Oh, the pity of it …
8th of 7, Aug 19 2012

       Why are we all of a sudden having trouble extracting bolts?   

       Left-hand drill bits, pilot hole first, threaded extractors, oxy torch. Lots of penetrine as lubricant and coolant for the drill bits.   

       Works *every time. Interested to hear where it doesn't.
Custardguts, Aug 19 2012

       It doesn't work when // all you have is an "ordinary hand drill" //, which is more deserving of pity than condemnation.
8th of 7, Aug 19 2012

       Welding to a broken bolt, even below the surface and building it up to above the surface where a nut can be welded on and unscrewed is the method I use. Rarely fail.
cudgel, Aug 19 2012

       Ah yes. Carpentry tools rarely, if ever, yield a positive result in steelwork.   

       Welding is good too, probably even better than the method I espoused, however it is slower, and there are some applications where the stray currents can be troublesome.   

       On the frame of a HV wound rotor motor, for instance.
Custardguts, Aug 20 2012

       Welding doesn't work on titanium bolts, the aluminum that the titanium bolt is stuck in goes all gooey. In fact even if you get a nicely seated extractor, you can get the bolt to turn, but you can see a portion of the aluminum panel in question turning with it. Then, either the extractor snaps, or the panel's junk. It's like the manufacturers of fighter jets actively wanted to sell more parts...
bs0u0155, Aug 20 2012

       Horror story: Broken exhaust studs in an aluminum head. R&R without removing the head or exhaust manifold (due to shocking placement of turbocharger requiring essentially stripping the engine to a long block to remove the manifold)   

       Snapped extractor: tears. had to pull engine, pull manifold and ruin four expensive drill bits to replace the stud.   

       Either the shank of the extractor needs to taper or the hole needs to taper. Having them both taper is silly and since it makes no substantial difference which one does the tapering you might as well have it be the extractor because then we can use a steep angled tool in a range of hole depth/size combinations. If the hole takes the taper then we must always use the same bore size (bit) which means having more extractors (and matching bits). It's not an improvement.
WcW, Aug 20 2012

       and the RAF don't allow the use of power tools on fighters, none.
bs0u0155, Aug 20 2012

       Do not forget dry ice, you bolt wranglers. Cold bolts get all wiggly and tractable.
bungston, Aug 20 2012


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