Broken bolt removal - best drill bit to use

[kbuhagiar]

Hello folks,

I am in the process of replacing the body mounts on my 56 Chevy One-Fifty.
After spending a few minutes it has become obvious that i will be dealing with a number of broken bolts that will need to be drilled out for removal.

All of these bolts are rusted/corroded. Several days of soaking in Kroil and applying heat have proved futile; two have broken off so far, and I expect the other two to do the same. These bolts are installed from below through the frame into blind captive nuts mounted on the body, which are not accessible from above.

Going forward, I will be drilling the bolts out and hoping to salvage the existing threads in the blind captive nuts. I'm not looking forward to it but I'm not too concerned as I've done this sort of thing before.

I'm willing to go out and spend a few bucks for new drill bits (any excuse for new tools!) - any recommendations for any particular drill bit brand or style that will make this a little less difficult?

Thanks in advance.

 

[clubairth]

I like Cobalt bits and if possible left hand bits. But good luck it seems like broken bolts never end!

If things really go to hell then a solid Carbide bit.
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[Rlfd213]

I use cheap bits but brand new ones. Also if you can use some heat and pB blaster before trying to get them off. Worst case if you can weld a nut to the top of the broken bolt and try getting it out that way

 

[ihateminimumwage]

A good set of Cobalt bits, oil and PATIENCE and you'll be fine.

Buy a helicoil kit in advance if/when one goes a little off center so you can just be done with it then and there.

 

[guppymech]

I like Cobalt bits and if possible left hand bits. But good luck it seems like broken bolts never end!

If things really go to hell then a solid Carbide bit.
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.
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+2 On Cobalt and L/H bit. Watch out with the heat you don't light your carpeting on fire, happened to a very sharp pal of mine.

 

[kbuhagiar]

Thanks for the replies so far!

As I mentioned in my original post, I am beyond the Kroil/PB Blaster/heat stage. The drilling will happen, not a question at this point, just looking for the best way to do the drilling.

Thanks again!

 

[JBradley500]

I’d be tempted to try those Matco Hyper-step bits for a job like that.

 

[ChevyEFI]

Cutting the floor, sometimes works best.

 

[plinker]

I’d be tempted to try those Matco Hyper-step bits for a job like that.

I had to remove a shock mount bolt (aluminum casting, blind hole) that the owner managed to break off & then tried to drill out (and broke a bit off in). Some Buick suv/mini van thing.

Anyway, it was a 14-2.00 bolt, I burred out enough of a taper and used the boss's 15/32 Matco bit and got the hole back to center from where it was drilled off center by the owner. Worked pretty well.

Heating may help soften the bolt, if it can be done safely with a torch. I've used HSS bits for the most part without much issue, right & left hand.

If you have a below surface broken bolt, a transfer punch can be useful to mark center to stat drilling.

Patience is the big thing.

 

[toplessHO]

for heat nothing beats welding a fat nut on the broken portion.
Idea is to weld from the inside and fill the nut up with weld.
then if you can get to any part of the threads,put some candle wax
to wick up in the threads

 

[Wamsutta]

Solid carbide bits and Proto square tapered bolt extractors.

 

[bora]

Could you not cut the floor from above , this would help a lot and also repair any damaged cages

I did this on my Gbody, pain but had to be done.

 

[Tallpilot]

I've had good luck with these.

https://www.circlecsupply.com/norse...MIwtGH9P2g4AIVAlcNCh0W1w0BEAQYAyABEgJvwvD_BwE

If it really goes south...

https://the-original-rescue-bit.myshopify.com

 

[Ign]

+2 On Cobalt and L/H bit. Watch out with the heat you don't light your carpeting on fire, happened to a very sharp pal of mine.

+3. KISS - you don't need anything fancy but LH bits

 

[fourjeepin]

for heat nothing beats welding a fat nut on the broken portion.
Idea is to weld from the inside and fill the nut up with weld.
then if you can get to any part of the threads,put some candle wax
to wick up in the threads

+1 weld a nut on and if the nut breaks off, weld it again. I’ve never had to weld a third nut on.

 

[kctyphoon]

If they’re getting drilled out anyway - what about some heat and some left handed bits as a last ditch effort.

They have induction heaters as an option, but it may not be practical for you.. how MUCH heat did you apply? How long, with what? You can often apply much more heat than you think. Induction heaters , from demos ive seen online, can get those bolts glowing. If youre using propane, you can try switching to map gas and really letting that flame sit on there..

 

[Benito]

I’d be tempted to try those Matco Hyper-step bits for a job like that.

That's pretty much why we have a set and use them on (often successfully). They sort of shave rather than take chunks out like normal bits

 

[theoldwizard1]

• Center punch (and it has to be CENTERED !)
• Use a pilot drill bit to get started
• Start with a small left hand drill bit
• Work you way up, staying with left hand bit if possible

Cobalt (M42) drill are very hard, as in BRITTLE ! They stay sharp for a long time. If it grabs, it will break.

M7 tool steel drill bits are less hard. M2 even less. The bit may wear faster, but it will have less chance of breaking.

 

[MoonRise]

The 'best' way I've found to remove 'stuck' and/or broken fasteners is to weld a nut onto the head/stub.

The intense heat helps loosen the rusted in place or seized threads, and the nut gives you a place to use a wrench.

I think I had to weld a nut onto a REALLY stuck fastener three times at the most (broke off the nut the first couple times). Annoying, but not a big deal. Just repeat the welding of a different nut into place and try again.

And there is a BIG difference between 'applying heat' and applying HEAT via welding or an oxy-acetylene torch.

Just like there is a difference in light output from a single birthday candle on a cupcake and the light output from an aircraft landing light.

Or you can try a left-hand cobalt drill bit.

Or a pencil die grinder and a small carbide burr and try to hollow-out the stuck bolt until you can either get the remains out or you grind out almost all of the metal and then you just have to use a pick to pick out the thread remains from the female threads.

But I now just go to the weld-a-nut approach unless I absolutely can't do that (like because of melting plastic panels or stuff like that).