PROBLEM - the majority of chain guards/protectors designed to keep your chain from damaging your frame can come loose - use a single pivot point for mounting - which means they can be bumped out of place - and they mount through the derailleur bolt (braze-on). The CLAMP-STYLE designs work perfectly, but can't be used on carbon fiber frames.
SOLUTION - I have developed a fixed chain guard solution for braze-on front derailleur systems.
I took a curved piece of T6 lightweight aluminum and shaped it - creating a stepped design that hugs the contours of your inner chain ring (with the chain on) with about 2mm of tolerance/space between the chain/chain ring and the protector guard arm.
This piece of aluminum is then TIG welded to the braze bracket - the part that is affixed to the frame (that the derailleur is mounted on.
The end result is a fixed (won't come loose - doesn't require the derailleur mount bolt to be threaded through it), aerodynamic solution that absolutely will not allow the chain past it. The guard arm is welded to the braze bracket - assuring that it won't move.
The two steps are designed to work with the curve of the arm to allow room for the chain and chain ring to operate without any contact with the guard, but also allow the guard to fit around them and under them (into the empty space below the spider/chain ring junction) so that the chain cannot jump off the chain ring.
Because it is fixed, rigid, and sits so closely to the chain, furthermore extending UNDER the ring - it is impossible to make the chain jump the ring.
I've tried. It won't come off the chain ring. Even when I set the derailleur stop point to allow ample room for the chain to jump.
>>>> I haven't decided if I will be willing to built any more - because this project was quite-frankly a major source of time-consumption. I had to measure the tolerances and then shape - measure - shape. Since chain rings can vary in thickness - crank sets can sit closer or further away from the seat stay (where the braze mount is located) there's no easy way to create a "one-size fits all".
It was custom built for my bicycle and I'm not the best welder in the world, so the weld joint is actually pretty ugly. LOL.