Filing a FD clamp?
 

So, my 1983 Schwinn SS SP is coming together nicely, but the FD I am hoping to use has a 28.6mm clamp where as the OD of the seat tube is 28.8mm without paint. I figured that, even after paint, I'll only need to remove 0.4mm or so and its not a part that is prone to failure (unless it has a plastic or CF clamp).

I'm pretty set on the FD I want to use, a reverse pull Suntour SL, which I've only been able to find with a 28.6mm clamp. The original FD was an "infinity clamp" Suntour M-II which I still have but its in rough shape and I love the reverse pull on my other SL FD bike.

So, have any of you done this? Would you do so in my situation? How should I file the clamp so that I get a consistent size all the way around?

Thanks

Schwinn SS SP? SL FD bike?


I am sure it can be done the issue would be removing the material evenly all the way around the inside. Since it is aluminum you most likely need to use an actual reamer or lots of aluminum sand paper.

I did this to get the FD on my Schwinn SS. As I remember, I used a metal file that was rounded to just under the profile needed for the FD. It took quite a while, and was a bit tense knowing the FD was likely going to be unusable if I managed to mess it up. Filing at the ends of the clamps is where most of the material was removed to allow it to go over the wider tubing. In the middle I did remove some, but the clamp itself can bend a bit to get the new radius. Wound up using the same bolt on the clamp as on the other bike. Left a bit more of a gap when clamped than on the old frame, but works just the same.

I guess I'll just have to go for it. I was thinking of removing a fraction extra and shimming with something that might be able to make up for any inconsistencies in my filing.

You could get a decent half-round file as Chrome Molly suggested, and you won't need any shims because you'll be able to get a very precise fit quickly.
This is aluminum, so a coarse file might be best.

Alternately, a piece of coarse sandpaper wrapped half-way around a standard seat tube should produce a proper radius by sliding your derailer up/down along the sandpaper covering the tube. Should cut very quickly depending on grit selected.

Perhaps use tape first to adjust diameter and protect paint as needed while sanding.
And I hope it goes without saying that the grit faces away from the tubing!