How to extract a VERY stuck screw

[John Coloccia]

Just wanted to post a little technique I use sometimes when things really go wrong. I think a lot of old timer machinists have probably seen this, but it's rarely talked about and can really save your bacon some day.

Anyhow, my first thought is always to try wedging the next size up allen key in there and see if it moves. For example, this is an M4 (4mm) bolt. Next size up is 1/4" hex key...you often have to go to a different system to get a good fit. Anyhow, that didn't work. Why? Well, this was on a motor coupling. These usually NEVER come off for the life of the machine and you tend to really crank down hard on them. No way this was coming out with that trick. Next thing I tried was a screw extractor. Drill through the head, twist it in and out it should come. I happened to have a kit laying around...not sure for what since I rarely ever need on, but there it was. My first tip off should have been that one was missing. Well, now two are missing, with the other half of the one I tried tonight buried firmly in the bolt. Here's a little hint....don't buy cheap, Chinese extractors. Despite being absolute garbage, they are still hardened like taps and there is no way in the world you will ever drill it out. This severely limits your options, as option #3 is usually to drill the head off and then there are any number of ways to gently drive out the screw once the pressure is relieved. Now that's impossible because the extractor is in the way.

Here's the victim. You can see I've already started doing something to it. Documenting this was an after thought. Note the little dimple on the head to the left. That's a center punch.
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Now I drill a 3/32" hole through the side of the head. It's fairly important that you drill straight and don't wobble too much. Here's where having a good feel for drilling freehand can really turn an otherwise show stopping heading into no big deal.
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Why 3/32"? Well, this ain't my first rodeo and I just happen to have a broken 3/32" drill bit laying around for just such an occasion. On a larger bolt, use a larger bit. I often keep old bit around for things like this. I also use them as alignment pins...what better alignment pin to stick in a 1/4" hole than a 1/4" drill shank? :) I suggest you break or cut it off at the flutes as it WILL break there anyway and it's potentially very dangerous.

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Grab my spoke, give a little turn and presto. From major problem to minor inconvenience in just a few minutes.
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Now, you may only get a 1/4 turn. That's not enough, so you have to so this multiple times. If your drilling is sloppy, you will need to really slow down and concentrate or will run out of room very fast and have a hard time getting this to work. This particular one took three spoke holes until I could grab it with pliers and pull it out.
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Hope this helps someone when you have a difficult extraction to do with partially buried bolt head. :)

[Ted Calver]

I think that's how the dentist did my last extraction!!

[mickey cassiba]

Very nice John...I've often had to follow failed attempts at screw extraction. Here's hoping a lot of folks read this. I'm slippin' this into my bag of tricks, I never thought of this route.

[Gary Kman]

I would have tried heat from a torch to relieve the torque and break the bond. If the part is aluminum you can remove a broken tap or easy-out by boiling in a water/alum (hydrated potassium aluminium sulfate) solution.

It is normal for a screw extractor (easy-out) to break unless the sticking torque or force is reduced first. Sometimes the head breaking off a cap screw does that if it isn't bottomed in the hole. Even though screw extractors are made of the highest strength alloy available, it's breaking strength is dependent on its cross-sectional area which is proportional to the square of the diameter.

[Ole Anderson]

Thanks for the tip, very neat. Socket head screws are usually grade 8 hardened so I'm surprised that you stripped out the head with the proper sized wrench. Did it fit snug and did you have it inserted all of the way? Possible it was set with red locktite. I understand some heat will release the grip of the locktite, worth a try next time,

Recently I broke the grade 8 bolts holding the straps on the u-joint of my Jeep's driveshaft. I asked the guy at the parts counter for a drill and matching easy-out to try to get it out. He said good luck with the hardened bolts. He suggested using a Dremel tool to flush the broken screw, then use a dremel cut-off wheel to cut a slot for a flat blade screwdriver. A small drum sander on the Dremel also adjusted the width and thickness of a screwdriver bit to fit the new slot exactly. I overcut the slot extending it into the pinion yoke to make sure I had a good deep slot in the 5/16" screw and out came the broken screw first try.

If you use an easy-out, the hardest part is accurately center drilling the rough end of the broken screw. Again the Dremel works wonders. Flatten the broken end with the tiny drum sander, then use a cone abrasive bit to make a serious indentation in the center of the screw to provide a fail safe starting point to start the drill.

[John Coloccia]

Hardened bolts drill fine. Sockets are typically class 12.9, but even that drills with no problem (roughly equivalent to Grade 8). Making a flat for a screwdriver is an age old trick but that wouldn't have worked in my case as there is no way to make a flat without destroying the part. If I wanted to do that, I would have just cut off the coupler in 2 seconds and called it a day.

If you want to get good at drilling things dead center, build an aluminum airplane. You'll either get very good at drilling out rivets or you'll get good at order new parts.

[Phil Thien]

Nice job.

But why are you removing couplers from your brand-new CNC machine?

[John Coloccia]

Nice job.

But why are you removing couplers from your brand-new CNC machine?

Hey, good question :)

Well, I'm building it myself. Bought the frame....motors...controller...driver...wiring...b oxes...inverters...spindle...etc. Definitely not plug and play, but I have a long history with robotics so I'm pretty squarely in my comfort zone. I was removing the bolt because I didn't like how it felt when I went to torque it down. I could feel it stripping. It was probably tight enough, but I wasn't sure so the right thing to do is toss the bolt and replace it. Every now and then, I get a bad socket head that just doesn't seem to be hardened properly. I confirmed that drilling it because it drilled like butter. It shouldn't be impossible but this felt like I was drilling mild steel. Anyhow, I couldn't back it out...the damage had already been done AND it was torqued down quiet a bit and buried so the normal tricks were impossible. These couplers are just a couple of bucks each. You'd normally just cut it off, replace it and move on, but that would have stalled the entire project because I don't have these kicking around the shop.

[Kent A Bathurst]

HUh. Go figger.

One of those "slap-your-head-why-didn't-I-think-of-this".

Thanks, JC. Excellent grooming tip.

Right up there with Red Green using the battery-powered hand mixer to raise and lower his hand-crank pickup truck windows. It's obvious, once someone points it out to you.

[Grant Wilkinson]

Tks for this JC. One thing that I have found, too, is that using a regular right hand drill bit to drill for an easy out can cause the bolt to tighten even more. A local hardware supplier here has bubble wrapped individual easy outs that come with the correct size left hand drill. I've had much better luck with them than when I was drilling normally.

[ray hampton]

Tks for this JC. One thing that I have found, too, is that using a regular right hand drill bit to drill for an easy out can cause the bolt to tighten even more. A local hardware supplier here has bubble wrapped individual easy outs that come with the correct size left hand drill. I've had much better luck with them than when I was drilling normally.

It never fail that if I think of a idea like using a left-hand bit but someone will reach the finish line first

[Jason Roehl]

I've drilled out screws/bolts before with a RH twist bit. Size it to the minor diameter of the threads of the fastener, and once you get down into the shaft, the threads will often just ride the bit out. Centered and straight are obviously important.