Braze-on front derailleur

[mugwump]

Can someone tell me how a braze on derailleur attaches to the bike
frame? I'd go to a LBS and look but there are no LBS's within 100
miles of where I live. Are there screws that go into brazed on
threaded sockets, or are screws brazed onto the frame, or what? What
diameter screws and thread pitch?

I am building a recumbent bike and need to mount a front derailleur on
a piece of CF tubing that is 34 mm diameter. I have no problem
drilling holes in the tubing and installing threaded inserts if that
is what it takes... The tubing will only be there to support the
derailleur, maybe a headlight, and a computer so it will never be
loaded like a normal seat tube.

Thanks!

 

[JeffWills]

mugwump wrote:
> Can someone tell me how a braze on derailleur attaches to the bike
> frame? I'd go to a LBS and look but there are no LBS's within 100
> miles of where I live. Are there screws that go into brazed on
> threaded sockets, or are screws brazed onto the frame, or what?
What
> diameter screws and thread pitch?
>

The mount is usually cast in some fashion, and then the derailleur
bolts to the mount. Take a look at the Silva Art. 291 and the Everest
C-134 on this page: http://www.framebuilding.com/Bosses.htm

> I am building a recumbent bike and need to mount a front derailleur
on
> a piece of CF tubing that is 34 mm diameter. I have no problem
> drilling holes in the tubing and installing threaded inserts if that
> is what it takes... The tubing will only be there to support the
> derailleur, maybe a headlight, and a computer so it will never be
> loaded like a normal seat tube.
>
> Thanks!

If you're mounting the derailleur to a 34mm piece of tubing, why not
get a derailleur with a 1 3/8" clamp and shim it? (1 3/8" ~= 34.9mm).
In fact, many "clamp-on" front derailleurs are braze-on derailleurs
mounted with this clamp:
http://harriscyclery.net/site/page.cfm?PageID=49&SKU=DP6200

A friend of mine built a carbon-fiber highracer and simply used a
normal clamp-on derailleur in front. You can see photos of the bike at
http://homepage.mac.com/john4bho/iblog/ , about 2/3 of the way down
(February 10th installment).

Jeff