I have some Cannondale carbon forks with an alu crown which don’t have any holes for mudguards or lights, and I’m thinking about putting an M5 hole into the front. Anyone done similar as lived to tell the tale? I’m not sure we’re the joint between the crown and the carbon legs is, but presumably a fair way down from the steerer tube.

Otherwise I suppose I could do something ugly with epoxy which might be a bit less hazardous. Hmm.

Just thinking about this gives me the fear. No way I’d drill that.

Is there a hole underneath?

Wedge a thing in there, bracket for the light out front and straight through the guard into bung for the mudguard.

Will look neater than the ftont hole aswell.

^ this is the way to do it if the crown is open underneath.

Assuming they’re made the way most Al-carbon mix forks are made you’ll be able to tell where the Al crown forging ends and the carbon leg begins with light taps from a small allen key or similar, the sound changes when the fork leg is hollow. It’s likely to be 300-320mm from the axle, or that general area. The crown itself, if forged Al, might be OK to drill into and tap. But I wouldn’t… You’d need to be 100% sure that you weren’t damaging any join between the crown and steerer and that’s much more difficult to figure out than where the crown/leg bond area is.

For the otherside I would drill it, but making sure the hole is drilled well away from the edge and deburred properly.

It’s a component that’s been built to be very light so there’s probably not a large safety factor to deal with people introducing holes.
Probability of failure medium to high.
Severity of failure is high – new dentures easily.

I wouldn’t but if you choose to do so use a framework like below to make your choice

I have carbon Kinesis Pro6 forks which came with a tapped hole in the rear for mudguards. The paint blistered slightly on the front of the fork, and in realised that the alu insert ran all the way through the fork, so I drilled and tapped a hole in the front for a light bracket.
I decided I was OK doing this because the fork had an alu insert designed to take a mounting hole. I wouldn’t recommend drilling into your fork if it is not designed to take fittings.

If you are asking if it’s OK to drill a carbon fork you must never have seen an intact fork fail just through fatigue and general use.

How old is your fork? At what age abd usage would you replace it? Or just use it until it fails?

Either bodge it with a bung under the steerer or buy a different fork

One of these mounting bungs for Moto style mudguards would probably do the job:

https://www.sjscycles.co.uk/mudguards/sks-shockboard-shockblade-26-28-mounting-kit/

https://www.sjscycles.co.uk/mudguards/topeak-defender-rc1-internal-fixer-nut/

Probably other similar beasties on the market or rattling around in the bottom of someones spares tin.

If you are asking if it’s OK to drill a carbon fork you must never have seen an intact fork fail just through fatigue and general use.

I have seen a number of them.

Almost never at the crown.

Usually at the point where the carbon legs are bonded to the insert about 5cm down the leg.

Or at where the drop out is bonded in