[CountryB]

I'm posting this question on this welding forum because I think most of you do machine-shop work and probably deal with broken bolts a lot.

I'm trying to drill out a seized "Allen head setscrew" in an aluminum housing. The setscrew diameter is around 1/4".

I have tried a number of bits (cobolt, titanium, and standard hss bits). I cant seem to drill through this. Maybe the bits I'm buying at local HD are not as good as claimed. I'm using cutting oil too.

I went though about six 3/16" bits and a couple of 1/8" bits so far and hardly drilled anything (although I did make a small hole so far). I've been at this for hours and need more bits now.

What type of bit is the best for hardened steel?

[CountryB]

I've been researching this since my post and wanted to reply back on what I learned in case someone else can benefit. This was a nice "professional" overview of drill bits so anyone interested
https://www.youtube.com/watch?v=sykjB7fS1Po

Basically,
1) Carbon bits are the hardest. But not recommended for hand drilling as they are easy to break with any side loading. Use these only with a drill press.

2) Colbalt is next hardest and used for hand drilling. M35 grade is popular for hardened steel. There is also a M45 grade - but i have not seen any drill bit with this rating.

Coatings: Titanium-aluminum-nitride (TiALN) coating is best for hardened steel. Titanium-carbon-nitride (TiCN) is next best, followed by the more typical Titanuim-nitride (TiN) coating.

Tip: 135 degree cutting angle is better than the 118 degree for cutting hardened steel.

[Oscar]

I agree,that cobalt bits would be your best bet. Find yourself some left-handed cobalt bits so the bit cutting action also serves to provide a counter-clockwise torque on the bolt to help free it up as you're drilling it.

[drizler1]

Have you tried a left handed drill bit. Might back it out. How bout penetrant and hammering with a blunted air chisel. Light limp wristed. Hammering will loosen and help drive the oil down. Try not to deform the head....I’ve seen that trick work wonders.....


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[Simclardy]

Dewalt makes a multipurpose carbide tip drill bit. It is sharp unlike a cement bit. It's the only thing that worked for drilling my safe...... promise it was my safe. Lol

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[weldin mike 27]

This isn't the video I was looking for, but forget the drill. https://youtu.be/5YSjmhPUhvs. Dissolve it.

[CountryB]

I see the carbide tipped bit listed under "masonry bits" on the Dewalt site. https://www.dewalt.com/products/accesso ... drill-bits

I've tried masonry bits before but hey didn't have the right cutting tip/angle for metal, or perhaps mine were not sharp enough due to use with masonry (but I think masonry bits are intended for use with an impact drill).

I could not tell from the picture on the Dewalt site if their carbide tipped bit had a cutting edge that would work for metal - but HD sells it so I'll give it try.

[MinnesotaDave]

A straight flute solid carbide drill bit will likely do the job for you.

[Darrin]

What drill speed are you running? We used to drill out titanium bolts all the time no problem, low speed no lube/oil.sounds like you’re doing things right, 3/32 ish to start and work your way up, then easy out or lefty bit.

[CountryB]

I'm using a hand drill (a Dewalt 18V). It runs at 450 rpm or 1500 rpm - I using the high speed setting. I got the Dewalt "cobalt" drill bit set mentioned above - but they wont dill through this Allen head set screw either.

I am making some progress (I'm about 70% through it) but it is taking a long time to make any progress. I would say I have been drilling this same set screw now for over 3 hours (not continuously but over a couple of days). I'm swapping to new bits and trying different sizes as I run through my drill bit sets. I'm oiling the bits (with cutting oil) and using quite a bit of pressure, but I'm mostly making fine metal paste rather than drill shavings.

I ordered the Dewalt Carbon-tip bits yesterday. They should be here today. I post back if those work better.

If I wasn't so suborn, I would give up on repairing/reusing this threaded hole, and just drill and thread a new hole for a new set screw.

[JayWal]

I had a guy bring me 2 bearing collars with a seized set screw in each, AND he’d broken of an Allen wrench in each. Needless to say hss bits didn’t even scratch it. I did have a solid carbide drill bit lying around and I used that on the first one. It drilled out that Allen like it was cheese. But yes, they are very brittle, half ways through the second one it snapped. I used a thin pointed carbide burr on a die grinder to get through and remove the second one.


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[Simclardy]

I keep extras because they break easy easy.

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[Simclardy]

I keep extras because they break easy easy.

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[BillE.Dee]

On broken studs, I've always started out as small as possible, then worked up to a bigger left hand drill bit with the thought that IF the bit took hold it would back out the broken stud as it was still drilling a hole. With the allen head bolts, which are usually pretty hard, I have used left handed bits that just caught the edges of the hex sides. Also usually learned a whole new vocabulary and did a lot of walk aways to calm the nerves. Good luck and keep us posted.

[Simclardy]

On broken studs, I've always started out as small as possible, then worked up to a bigger left hand drill bit with the thought that IF the bit took hold it would back out the broken stud as it was still drilling a hole. With the allen head bolts, which are usually pretty hard, I have used left handed bits that just caught the edges of the hex sides. Also usually learned a whole new vocabulary and did a lot of walk aways to calm the nerves. Good luck and keep us posted.

Sounds good. I will have to try that.
Another method i use is, tig weld a nut or something to grab. The extreme heat and ability to grab the bolt usually does the trick

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[Simclardy]

On broken studs, I've always started out as small as possible, then worked up to a bigger left hand drill bit with the thought that IF the bit took hold it would back out the broken stud as it was still drilling a hole. With the allen head bolts, which are usually pretty hard, I have used left handed bits that just caught the edges of the hex sides. Also usually learned a whole new vocabulary and did a lot of walk aways to calm the nerves. Good luck and keep us posted.

Sounds good. I will have to try that.
Another method i use is, tig weld a nut or something to grab. The extreme heat and ability to grab the bolt usually does the trick

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[Simclardy]

Sorry, my phone is making duplicates. Arrr the first time i send nothing happens. I wait 5 minutes and finally hit it again and it sends 2.

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[CountryB]

I was able to drill it out with the Dewalt Carbide tipped bit. I was still tough.
Once I got a hole all the way through it, I needed to drill for tap size. I wasn't getting anywhere with the colbalt bits so I decided to try and use my bench-top drill press. The reason I didn't use the press in the first place is because the shape of this part meant I had no way to clamp it in position and would have to hold it by hand. So I held it by hand, and with the drill press I was able to drill it out to 5/16" pretty fast. I bet if I started with the drill press I would have had this drilled out in the first hour with just the cobalt bits.
So job done now.

[CountryB]

I was able to drill it out with the Dewalt Carbide tipped bit. It was still tough and slow.
Once I got a hole all the way through it, I needed to drill for tap size.

I wasn't getting anywhere with the colbalt bits so I decided to try and use my bench-top drill press. The reason I didn't use the press in the first place is because the shape of this part meant I had no way to clamp it in position and would have to hold it by hand. So I held it by hand, and with the drill press I was able to drill it out to 5/16" pretty fast.

I bet if I started with the drill press I would have had this drilled out in the first hour with just the cobalt bits.
So job done now].

[BillE.Dee]

Talk about strange happenings. I had some pipe positioners I wanted to clean up and sell, and sure enough broken studs. The first one, drilled hole as close to center as I could get and used a small chisel against the protruding edge,,out it comes. The second one I ended up drilling several times as close to the threads as possible and retapped it. My vocab is growing and I need a new pair of boots--wore the old ones out walking away.

[LtBadd]

Talk about strange happenings. I had some pipe positioners I wanted to clean up and sell, and sure enough broken studs. The first one, drilled hole as close to center as I could get and used a small chisel against the protruding edge,,out it comes. The second one I ended up drilling several times as close to the threads as possible and retapped it. My vocab is growing and I need a new pair of boots--wore the old ones out walking away.

Bill, have you ever tried, if the broken bolt isn't too far below the surface, welding a short socket cap head screw to the stub, let it cool then use an allen to back it out?

I've done this many times successfully with broken off taps as well, doesn't alway work but might be helpful sometime.

[BillE.Dee]

Hi Richard, I have had a few shots are welding a nut over some protrusion and gotten the broken studs out. The way everything is going lately, I almost need a snorkel to get hold of the broken studs. HOwever I will remember the short allen stud trick. Do appreciate the advise and all of the help you and other folks provided me and others.
Bill

[JayWal]

Has anyone every used stick rods made just for extracting studs? I keep seeing them at my WS wonder if they actually work. According to the label you stick it straight down into the hole, it welds onto the broken stud or tap, the flux coats and protects the threads of the hole and you weld a nut to the other end and twist it out. Seems intriguing and a load of BS at the same time.

Sorry if I’m hijacking this thread btw.

[MinnesotaDave]

Has anyone every used stick rods made just for extracting studs? I keep seeing them at my WS wonder if they actually work. According to the label you stick it straight down into the hole, it welds onto the broken stud or tap, the flux coats and protects the threads of the hole and you weld a nut to the other end and twist it out. Seems intriguing and a load of BS at the same time.

Sorry if I’m hijacking this thread btw.

I've not used them, but know people who have used them on heavy equipment. They report they work well.

[weldin mike 27]

The brand name ones are called xtractalloy. It's most certainly not bs, but I don't know how it goes on aluminium heads. I've seen some awesome photos of stuff on cast iron equipment. Really saves the day.