Need help-extracting hardened screws.

Forestgnome · Jun 26, 2017

I'm dealing with a recurring problem of broken hardened screws in a product my company repairs. The screw is used as a shaft for a clamping roller, and has a shoulder that extends down into the aluminum frame. At the end of the shoulder the screw is threaded M4. These screws are specified to be hardened to 53-60 HRC. The first one I extracted okay. I used a 1/16" carbide drill and my homebrew 4-sided extractor. I have been unable to get the next two out. My extractor is a broken tap ground to four sides, but the hardened screws just bite the edges down so it rounds off. I can get almost enough torque to break the extractor. These are specified to be installed using Loctite 222E (I've been unable to find specs on this, only on 222). I suspect maybe our customer has re-installed these with some really strong thread locker, as these won't budge, even with heat. I was thinking of just drilling the rest of the screws out, but the carbide drills I found are specified to drill up to 45HRC. I could just use inserts since the frame is aluminum.

Any suggestions?

adama · Jun 26, 2017

Weld something to em and they will undo easily. IMHO it's not the thread lock but disimilar metals and they will lock up way too well.

FredC · Jun 26, 2017

I have used welding as suggested when a little bit of the screw is sticking out. Welded a hex nut on and put a wrench on it and screwed it out. If these your screws are broken off below the surface that will not work so well. I just removed a broken off screw from a lathe bed, it was too hard to drill with a hand drill so I put it on the mill and used a 1/4 inch carbide spade drill. I thought I was dealing with a broken off form tap but the screw was probably 50 ish RC. The drill turned it a little so I knew it was not a tap. I then reground the spade drill to left hand, when the flutes got clogged up the drill spun the broken off remnants right out.

Since you mentioned Loctite, most break down in the 300 to 350F neighborhood, if you can put these things in an oven, the Loctite strength will be greatly reduced. If drilling with carbide a bushing to guide the drill will help out a lot, maybe 3mm or 1/8 inch spade drills would work for you if you can center them and keep from breaking out the side.

AARONT · Jun 26, 2017

Some heat and a good left handed carbide drill should get it to un-thread for you. If it doesn't un-thread, you may be able to drill it out.

gbent · Jun 26, 2017

My choice is welding where it is applicable, but an M4 requires a steady hand with a tig torch and filler. If its broken below the surface I wouldn't even try welding.

I would freehand grind a broken end mill into a point like Fred shows. If its locked up, left or right hand isn't going to matter much, it won't spin out anyway. I like to drill the thru hole about 1/2 the size of the screw. Make sure your screw extractor is sharp, regrind it when it starts rounding the corners. I prefer repurposed 4 flute taps such as you are using over anything store bought for hard screws or set screws.

Chip Chester · Jun 26, 2017

Stress riser at shoulder on the bolt? And +1 on dissimilar metals. And try the square tapered extractors instead of the spiral ones.

Chip

awake · Jun 26, 2017

If this is going to be a regular occurrence, is it time for a sinker EDM?

ezduzit · Jun 26, 2017

Yup...elox.

CarbideBob · Jun 26, 2017

AARONT said:
Some heat and a good left handed carbide drill should get it to un-thread for you. If it doesn't un-thread, you may be able to drill it out.

Agree.
If you can center over the hole accurately a hand made left hand spade from a old carbide1/8 endmill shank.
This leave you just inside the tap dimension so bent over pieces wedged in the threads move while the left hand tries to unscrew it as soon as it become free.
You normally don't drill much with this setup, just enough to get rid of the top where it has busted and is binding. The bit then bites and removes the screw.
You sort of poke at it, like tiny peck drilling. Best done in a B-port and you have to be ready to follow the screw up with moderate pressure on the quill handle.
You'll need the heat to handle the glue so it could be a two man job. One on the handles, one on the torch.
Bob

DDoug · Jun 27, 2017

if this is a repeat job, it might be a good idea to go buy a few headed drill bushings
that slip fit into the hole, allowing you to easily guide the drill.

Forestgnome · Jun 27, 2017

Welding not an option The screw is 3/8" down into a 5mm counterbore. I was using a drill bushing in the counterbore to use the 1/16" carbide drill. No problem drilling a 1/16" hole through. I was considering getting a 1/8" Omega drill to finish the job. Sounds like drilling it out is the consensus. As far as a shoulder holding it, the screw is undercut before the shoulder. That's where it breaks.

NAST555 · Jun 27, 2017

Forestgnome said:
Welding not an option The screw is 3/8" down into a 5mm counterbore. I was using a drill bushing in the counterbore to use the 1/16" carbide drill. No problem drilling a 1/16" hole through. I was considering getting a 1/8" Omega drill to finish the job. Sounds like drilling it out is the consensus. As far as a shoulder holding it, the screw is undercut before the shoulder. That's where it breaks.

Just a guess but that under cut is probably square with not much of a radius. It is amazing how much stronger a bit of a radius on the undercut on both sides of the shoulders makes a part. If you are part of/know who manufactures the bolts I would suggest a nice radius and even maybe a full radius at that point for the next batch.

Forestgnome · Jun 27, 2017

Undercut is radiused.

Krutch · Jun 30, 2017

I recently removed some small screws broken off below the surface by using a sensitive drill in a vertical mill and a 1/16 carbide mill. Once I had a hole in the screw I used a pointy needle file to back the screws out. They backed out freely. Had they been stuck it might have been a harder job to complete. A left hand drill is how I get most such screws out but didn't have one small enough for that job.

Forestgnome · Jul 7, 2017

Well I bought an Omega drill, and it's a beast. Went through it no problem. Was able to chisel out the rest of the threads (wish the chisel was as hard as the screw) and Helicoiled it.

mccolld · Jul 13, 2017

I'd put some heat on the Al. That should expand quicker than the screw and breakdown any adhesive.

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vancecam · Jul 13, 2017

Forestgnome said:
I'm dealing with a recurring problem of broken hardened screws in a product my company repairs. The screw is used as a shaft for a clamping roller, and has a shoulder that extends down into the aluminum frame. At the end of the shoulder the screw is threaded M4. These screws are specified to be hardened to 53-60 HRC. The first one I extracted okay. I used a 1/16" carbide drill and my homebrew 4-sided extractor. I have been unable to get the next two out. My extractor is a broken tap ground to four sides, but the hardened screws just bite the edges down so it rounds off. I can get almost enough torque to break the extractor. These are specified to be installed using Loctite 222E (I've been unable to find specs on this, only on 222). I suspect maybe our customer has re-installed these with some really strong thread locker, as these won't budge, even with heat. I was thinking of just drilling the rest of the screws out, but the carbide drills I found are specified to drill up to 45HRC. I could just use inserts since the frame is aluminum.

Any suggestions?

If it's the threadlocker that's making the difference, and if the part is not too huge, immerse it in acetone overnight and try your extractor again.

tew45 · Jul 13, 2017

Forestgnome said:
I'm dealing with a recurring problem of broken hardened screws in a product my company repairs. The screw is used as a shaft for a clamping roller, and has a shoulder that extends down into the aluminum frame. At the end of the shoulder the screw is threaded M4. These screws are specified to be hardened to 53-60 HRC. The first one I extracted okay. I used a 1/16" carbide drill and my homebrew 4-sided extractor. I have been unable to get the next two out. My extractor is a broken tap ground to four sides, but the hardened screws just bite the edges down so it rounds off. I can get almost enough torque to break the extractor. These are specified to be installed using Loctite 222E (I've been unable to find specs on this, only on 222). I suspect maybe our customer has re-installed these with some really strong thread locker, as these won't budge, even with heat. I was thinking of just drilling the rest of the screws out, but the carbide drills I found are specified to drill up to 45HRC. I could just use inserts since the frame is aluminum.

Any suggestions?

There are many ways to remove broken screws however removal is not the problem. The recurring part is! Use a more appropriate fasteners for the job.

jr2766 · Jul 13, 2017

Broken Screw or tap extraction

Forestgnome said:
I'm dealing with a recurring problem of broken hardened screws in a product my company repairs. The screw is used as a shaft for a clamping roller, and has a shoulder that extends down into the aluminum frame. At the end of the shoulder the screw is threaded M4. These screws are specified to be hardened to 53-60 HRC. The first one I extracted okay. I used a 1/16" carbide drill and my homebrew 4-sided extractor. I have been unable to get the next two out. My extractor is a broken tap ground to four sides, but the hardened screws just bite the edges down so it rounds off. I can get almost enough torque to break the extractor. These are specified to be installed using Loctite 222E (I've been unable to find specs on this, only on 222). I suspect maybe our customer has re-installed these with some really strong thread locker, as these won't budge, even with heat. I was thinking of just drilling the rest of the screws out, but the carbide drills I found are specified to drill up to 45HRC. I could just use inserts since the frame is aluminum.

Any suggestions?

If it is possible to submerge the part I'd suggest you consider dissolving the tap using Alum. I've attached a link to a You Tube video which will amaze you. Chemical Removal of a Broken Drill Bit or Tap With Alum (nonferrous) - YouTube There's no problem with the Aluminium being attacked - only the teel pert will be dissolved.

rogertoolmaker · Jul 13, 2017

Reduce the temper

Forestgnome said:
I'm dealing with a recurring problem of broken hardened screws in a product my company repairs. The screw is used as a shaft for a clamping roller, and has a shoulder that extends down into the aluminum frame. At the end of the shoulder the screw is threaded M4. These screws are specified to be hardened to 53-60 HRC. The first one I extracted okay. I used a 1/16" carbide drill and my homebrew 4-sided extractor. I have been unable to get the next two out. My extractor is a broken tap ground to four sides, but the hardened screws just bite the edges down so it rounds off. I can get almost enough torque to break the extractor. These are specified to be installed using Loctite 222E (I've been unable to find specs on this, only on 222). I suspect maybe our customer has re-installed these with some really strong thread locker, as these won't budge, even with heat. I was thinking of just drilling the rest of the screws out, but the carbide drills I found are specified to drill up to 45HRC. I could just use inserts since the frame is aluminum.

Any suggestions?

With a screw up to 60Rc I wonder if better control of the temper could eliminate the problem. A hardness somewhere between 45Rc and 52Rc max. and maybe with an alloy steel for less prone to breakage. I would take a close look at the screw design.

Roger 07/13/2017

Need help-extracting hardened screws.

Stainless

Diamond

Diamond

Stainless

Diamond

Diamond

Titanium

Hot Rolled

Diamond

Diamond

Stainless

Stainless

Stainless

Stainless

Stainless

Aluminum

Plastic

Plastic

Plastic

Cast Iron

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