The tap is singing!
The drill isn't making a sound at all,
but given the nature of the work, I'm including it under "The drill is singing!"
A customer brought in a Campagnolo right crank where
the threads in the chainring fixing bolt hole were stripped,
asking if there was anything I could do about it.
↑Right here.
Since this is a Power Torque and not an Ultra Torque,
removing the crank would be a pain, so I'll work with it as is.
↑The chainring fixing bolt is going in at an angle,
but there's a reason for that (more on that later).
The bolt threads are stripped,
and the crank side is also stripped.
Though the back part is still okay.
The chainring fixing bolt is M8 thread.
And standard M8 bolts have a pitch of 1.25mm.
However, the chainring fixing bolt has
an M8 pitch of 0.75mm.
I asked the customer if they could bring a tap and die—
if they provided the tools, I'd buy them from him.
↑With an M8×0.75 tap,
with a scraping sound,
it was more or less fixed.
The bolt side also made that scraping sound, but
we won't be using this one anymore.
I threaded the fixing bolt in by itself.
It goes in smoothly and straight.
So why was the bolt going in at an angle when it was brought in?
I installed 4 of the pins except for the one on the back of the crank.
On this Campagnolo crank, with a compact chainring,
not all 5 bolt holes have a 110mm PCD (pitch circle diameter)—
the one on the back of the crank is 113mm.
Someone attempted to machine this 110mm PCD chainring
by modifying just one hole to 113mm,
but the machining was incomplete, so the fixing bolt went in at an angle,
which resulted in the threads being stripped.
So I continued the machining until the fixing bolt
could go in straight.
The customer's spare fixing bolts were all aluminum
with damaged threads (I did run a die over them to make them somewhat usable)
so I swapped them out for a steel bolt from my own stock.
It's going in straight.
↑Before machining
↑After machining
You can see the claw-shaped gap on the inside is larger after machining.
The reason this fixing bolt gets destroyed so frequently
is that the crank is on a cyclocross bike
and the tooth count is changed depending on the course.
Companies like Strong Light make chainrings in 110/113mm versions,
so I'd recommend using those from now on.
By the way, the original machining of this chainring wasn't done by the customer.
The drill isn't making a sound at all,
but given the nature of the work, I'm including it under "The drill is singing!"
A customer brought in a Campagnolo right crank where
the threads in the chainring fixing bolt hole were stripped,
asking if there was anything I could do about it.
↑Right here.
Since this is a Power Torque and not an Ultra Torque,
removing the crank would be a pain, so I'll work with it as is.
↑The chainring fixing bolt is going in at an angle,
but there's a reason for that (more on that later).
The bolt threads are stripped,
and the crank side is also stripped.
Though the back part is still okay.
The chainring fixing bolt is M8 thread.
And standard M8 bolts have a pitch of 1.25mm.
However, the chainring fixing bolt has
an M8 pitch of 0.75mm.
I asked the customer if they could bring a tap and die—
if they provided the tools, I'd buy them from him.
↑With an M8×0.75 tap,
with a scraping sound,
it was more or less fixed.
The bolt side also made that scraping sound, but
we won't be using this one anymore.
I threaded the fixing bolt in by itself.
It goes in smoothly and straight.
So why was the bolt going in at an angle when it was brought in?
I installed 4 of the pins except for the one on the back of the crank.
On this Campagnolo crank, with a compact chainring,
not all 5 bolt holes have a 110mm PCD (pitch circle diameter)—
the one on the back of the crank is 113mm.
Someone attempted to machine this 110mm PCD chainring
by modifying just one hole to 113mm,
but the machining was incomplete, so the fixing bolt went in at an angle,
which resulted in the threads being stripped.
So I continued the machining until the fixing bolt
could go in straight.
The customer's spare fixing bolts were all aluminum
with damaged threads (I did run a die over them to make them somewhat usable)
so I swapped them out for a steel bolt from my own stock.
It's going in straight.
↑Before machining
↑After machining
You can see the claw-shaped gap on the inside is larger after machining.
The reason this fixing bolt gets destroyed so frequently
is that the crank is on a cyclocross bike
and the tooth count is changed depending on the course.
Companies like Strong Light make chainrings in 110/113mm versions,
so I'd recommend using those from now on.
By the way, the original machining of this chainring wasn't done by the customer.