Extracting a broken screw or stud

R

redcatrr

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Probably the most common type of machine shop repair is the removal of a broken fastener from a blind hole. Over the years I have tried drilling, milling, heat and Kroil, with my one success being a left handed drill on a 1/2-13 main cap bolt. Usually my efforts result in a drill, mill, tap, or ease out being broken off in the fastener I'm trying to remove, and the piece going in the scrap bin.

I know that there are people who can do this, can anyone shed light on the magic? For the purpose of this discussion, assume that the broken fastener is in a blind hole, below the deck surface.

Thanks,

Kevin
 
My only success has been in using diamond burrs and grinding out broken taps and hard bolts. If it is a soft bolt I have used LH drills with good success.
Use lots of lube with the burrs to keep them from overheating and wearing out too quickly.
Fortunately I have not had to use the sevices of a Ram EDM to burn one out. YET
 
I have had pretty good luck with the "Pro Grabit" screw extractors like the ones seen here

http://kbctools.com/usa/Navigation/NavPDF.cfm?PDFPage=862

Mainly I have used them on soft bolts that I twisted the heads off of. Not sure how they would work on seized bolts. I have also managed to drill out broken screws/bolts in the past using HSS bits. I have heard of half a dozen ways to remove broken fasteners; probably pays to keep a couple in your pocket.
 
Your dentist may give you some carbide and/or diamond burrs if you ask, that will fit a Dremel tool.
 
Moparfever said:
I spend a lot of time and care getting the first drilling centered. If at or above the surface, I file it flat before center punching it. If below the surface, I'll center punch it perpendicular to the surface, whatever angle it is. Then I start with a very small drill. If I was able to flatten the surface, I just drill it straight in to a depth I know I won't exceed during the process of removal. I plan on possibly mucking up the first attempt, so I plan on being able to use two successive sizes of extractors by drilling a smaller hole first. I always start with the smallest possible pilot hole to make sure I'm centered. If the surface is at an angle, I'll start drilling perpendicular to the surface, then after a good start I start straightening out the drill until it's running on axis. The idea of getting it perfectly centered is that the last ditch effort will be drilling it out until there's nothing but thread left, then picking out the thread with a pick. I try to avoid the high helix type of extractors, as I find they tend to swell the walls of the screw making it tighter. This is especially true if the hole is drilled too big, making the walls thinner. I prefer the slower helix or straight flute extractors. As you probably know, left-hand drills work great sometimes pulling the screw out as you remove material. Again, I always start out with the idea that it may take several attempts.
Click to expand...

It appears that moparfever & I had the same teacher. I do the exact same thing that he does even down to making sure that the hole is started perfectly centered. If you have to, you can drill with successive bits until you see some threads. Once you see the threads you can take a pick or scribe & try to pick the remainder of the thread out. You can also sometimes get a torch with a real fine blue tip flame down into the hole & burn out the thin remainder of the broken bolt without damaging the threads. Another trick that I've learned is to drill a hole in the broken bolt a little undersize , heat the bolt red & then drive a torx bit in the hole. You now have a torx head bolt to remove instead of a broken head bolt! It pays to put pressure on the end of the torx bit to hold it straight in the hole while turning it out.
Hope this helps someone,
Phil
 
I've had a set of extractors for years that look a little like torx bits. Small splines that are spaced widely. They work incredibly well since they don't expand the bolt and are tough enough for impact with a square socket.

If the piece with the broken bolt owes me a lot of money, and I have to use a hand drill motor. I'll take a bench block, drill a hole to guide the pilot drill, add a counter bore on the bottom to hold a guide. I'll turn the guide in the lathe to center the transfer punch and help keep the pilot drill straight. 1/2 the battle is getting the hole on center and straight. It is a little embarrassing when you go through all that setup and the bolt backs out as soon as the Left handed drill bit hits it. Glad you did it when the thing turns out to be rusted/bottom bound.

Steve
 
DMS said:
I have had pretty good luck with the "Pro Grabit" screw extractors like the ones seen here

http://kbctools.com/usa/Navigation/NavPDF.cfm?PDFPage=862

Mainly I have used them on soft bolts that I twisted the heads off of. Not sure how they would work on seized bolts. I have also managed to drill out broken screws/bolts in the past using HSS bits. I have heard of half a dozen ways to remove broken fasteners; probably pays to keep a couple in your pocket.
Click to expand...
I know the guy that invented and makes the Grabit screw extractors. I know the whole family, and I. Built a few homes for the family. It took them a few years to get the alloy right for the right amount of hardness and toughness. Its a closely guarded secret. I don't exactly know what the alloy is but its not your everyday tool steel, he won't tell. They work most of the time. Heat and penetrants help on rusted bolts sometimes. A little bit of impact can work too to open up the threads a little. Nothing is a guaranteed success though.. some of these broken bolts require a lot of creativity. ;)
 
I've tried must of these tools over the years, some work some don't. I usually just build up the screw with a wire welder then weld on a nut, let the heat soak through then spin it off. If the weld twists off I try a small stainless steel stick rod. Almost always works. If not dig out the carbide drills.
 
The trick to welding on the nut is to let the stud cool off completely. As the stud cools it shrinks because when the stud is heated it can only expand upward and not out into the threads. Therefore when it cools it will shrink away from the threads. A lot of times if you try to remove it while its hot, it is expanded into the threads more than before you heated it and it will gall. Usually works for me.

Patrick
 
have had good success by welding a smaller washer over the broken stud. Let it partially cool then weld a larger nut on the washer. As this cools I rub a candle on the work and the nut/ washer combo.
Get a cup of coffee and by the time you pause to think just go screw the nut out. I always tighten the nut SLIGHTLY just 10 to 15 degree rotation. 90 percent of the time the nut/washer/ and the broken stud will back right out.
The candle wax will penetrate very easily and lube while removing.

hope this helps
alabamaed36046
 
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