I'm replacing my mudguards but, in removing the rear one, the head came off one of the bolts. As you can see from the photos, drilling has only got so far and I think I'm doing more harm to my tools than the bolt.

get yourself a dremel and cut-off wheel, cut a slot in the stub and use a screwdriver to unscrew it out the inside of the dropout

I've had success in the past with pounding a hex wrench into the bolt head and turning it out. Or if too far gone, epoxy one in and turning the bolt out. Of course you'll need to replace the hex later. I've never had much luck with e-z outs but probably just me. Did you use PB Blaster or other penetrating oil before trying to remove it?

You using carbide drill bits? Those're meant for use on harder stuff, but they break easier (being rather brittle), work better at slower speeds with lubrication between drill tip and item being drilled out.

Too, sometimes it's worth trying to make a stuck bolt even tighter first; turn it to the right before going back counter-clockwise to loosen. 'Course this is opposite to what you want to try if it's a LEFT HAND threaded fastener! (You confident those bolts are right-hand threaded?)

There is no head - it came off easily. Image 2 shows how I've tried to drill into it's former location.

They're basic threaded - clockwise to tighten etc. There's no head on the bolt - it came off easily. I haven't a clue what my wee bits are made of.

Keep drilling, maybe with a smaller bit.

So far you've done a pretty impressive job of drilling right down the center of the bolt but I would try a smaller diameter bit first to drill all the way through then, if needed, increase the bit size. You might get lucky with the smaller or larger bit, and it will catch and spin the bolt out. As mentioned already, first use some good penetrant like Kroil or PB blaster and soak for a day. You can also use a sheet metal screw as an "Easy Out" type of tool since you don't need reverse turning to remove that bolt. If you have some good vice grip pliers you may still be able to grab that stump and remove it but clamp it on as hard as you can.

I've snapped more Chicom stainless hardware than I care to remember. Stainless is hard to drill. Try Left hand drill bits so you're actually trying to unscrew the bolt as you drill. Available at most hardware, auto parts Harbor freight etc/

Looks like the hole you drilled is already way off center and will cut some of the threads on the frame. You'll be surprised how easy the remains of that bolt might come out with a few blows on a well placed and sharp cold chisel corner placed on the outer edge and hit with hammer in the direction you want to turn it. Don't be shy with the hammer blow.

+1 to this..

the tapered shape of the "stub" will, most likely, mean the vise grip idea is not going to work.
someone suggested grinding a slot/ use screwdriver method... won't work on a screw that's so stuck in the aluminum that it broke, but Does Work for a bolt that broke from over-tightening!
i like using left hand/reverse direction drills on blind hole broken bolts/screws... the drilling process creates Heat that can break loose a stuck bolt or screw.

one thing though... ANY lube on the screw, WHEN DRILLING, will have the drill not penetrating the broken screw, and that will then cause advanced wear of the drill as it work hardens the screw material.
clean off any lube Before Drilling.
Excess RPM can and will work harden the surface, and also Rapidly Dulls the Drill Bit.
people then tend to press harder, which then snaps the small drill bit...

As the head and some of the bolt is gone, weld a nut to the bolt that remains on the inside, and unscrew it from the inside.

it's a 5mm screw... the chisel drive method won't work.

I've done much smaller. And they were broken flush to what they were screwed into. But I also have some small and very sharp cold chisels.

I'm not certain why the OP can't grab the other end with a good pair of vise grips and twist it out. But since the end is really buggered up, I figure they don't own a decent pair of vice grips.

I don't have them - I'm considering whacking with a woodworker's nail punch.

I’ve had good luck with carving two flats (dremel and cut-off wheel again) into the bolt stub and using small vise-grips or even an adjustable wrench

the screw threads are corroded to the aluminum dropout... that is why the screw broke.
the stub sticking out is buggered up from attempts to do what so many say can be easily done.

the corrosion will need to be broken loose before that screw will ever turn.
drilling and a properly sized easy out is the best course, After more penetrant, and/or heat cycling is applied.
too much heating will damage the paint in a 1 to 2 inch radius... or more.

No need for a left-hand bit in this situation. A standard right-hand bit will be turning the correct direction to twist it out towards the inside of the dropout.

5mm bolt, start with a 2mm / 3/32" bit, no larger.

a trick i've used in the past... stick an Arc welding rod to a stuck screw... then use the arc rod to back the screw out... and the heat cycling from the arc process loosened the corrosion bond too... there is an actual Dedicated product for this procedure... any welding supply house would know if they're still available... it's worth a call, eh?

i've seen an Auto Body shop dude use something similar.. the guy used a bolt of a slightly larger size, and then used a Spot Welder to stick the bolt to the busted bolt, in a threaded blind hole situation... and, once again, the rapid heating aided in corrosion destruction .
it was a small fender mount bolt... and the AB man was a veteran of the trade. A 6x1 metric bolt in a toyota

i've welded a nut to a protruding broken bolt several times... Ag. tractors and golf mowers, mostly.
yep, they came out, except one on a long-retired path sweeper... i then cut/drilled/retapped that one.

True but ONLY when drill is employed to drill into the fastener from the front end, as the OP appears to be doing. LH drills are fine when your only approach is from the head end.

This has turned into a comedy of "expert" advice that makes no sense at all to me. The screw is for a simple mudguard strut !

It doesn't need threads at all. Drill out the fastener whether it is perfectly on-center or not. Just put a gol-darn 5.5mm hole in the dropout and use a allen screw and a nylok bolt.

I'm shaking my head here. Whats next ? Start sending him to find an EDM shop ?

It's a goddamn bicycle, not the Space Shuttle !

^^This. With the added comment: Take a hammer and round punch, perhaps 3mm diameter, and hit the bolt (axially) stoutly from each side, in an attempt to drive the bolt across any slack in the threads, to loosen the bolt. Back and forth, alternating hitting from both sides. DON'T use a pointed (center) punch, that will make the bolt ends tighter. Then try to turn it somehow.

I had a bolt break off flush, it was a long rack bolt and probably came loose. Fortunately, using a dental pick, I was able to back out the threaded portion as it was not tight and was lubed with anti-seize. AFTER THAT... I replaced all rack bolts with ones that protruded to the inside by at least a nut thickness. So...
- If the bolt breaks, I can grab the other end to back the bolt out.
- After normally tightening the bolt, I put a nut on the protrusion end and torqued it mildly, to lock the bolt in place. Never comes loose. But if needed to, it is anti-seized to come out easily.
- Use stainless steel bolts.
- Torque to spec with a micro-torque-wrench, if you have one.
- Mark 12 o'clock position of bolt head as easy indicator if bolt is coming loose.






"Go in peace." - Jules, Pulp Fiction

I've bought a set of 3mm HSS bits and I'm going to drill till the cows come home. If the threads are wrecked, nut and bolt will sort.

You could also helicoil the hole to restore the threads. That actually makes the threads stronger, especially in aluminum, with a stainless steel helicoil. My old company's products, aluminum, came from the factory with all threaded holes helicoiled.