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Old 06-03-20, 12:08 PM
  #83  
scarlson 
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Join Date: Jun 2010
Location: Medford MA
Posts: 1,770

Bikes: Ron Cooper touring, 1959 Jack Taylor 650b ladyback touring tandem, Vitus 979, Joe Bell painted Claud Butler Dalesman, Colin Laing curved tube tandem, heavily-Dilberted 1982 Trek 6xx, René Herse tandem

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So, I banged out the front derailleur. What a pain to build! I'm going back to my roots, as I have no machine shop, filing and scraping metal in the basement.

Here it is, in stages.

First, since I have no more heavy tooling, I bought some metal-cutting jigsaw blades and a 50-pack of cheap hacksaw blades from Harbor Freight. I think this was $10 for everything. Then I used a jigsaw left behind by the previous owner of my apartment to saw out the derailleur cage. But it turns out a sharp hacksaw is less onerous and takes just as long and can cut just as tight of curves. This is all in 14 gauge stainless, so it really sucks to work with! The original Herse front derailleur on my tandem is 2mm steel, so 14ga is a bit thicker, but the closest readily available substitute in the USA.


Then I ganged some hacksaw blades to slit the pushrod so I could braze the cage in place. I was confident I'd heard of this technique from an oldtimer, but I can't find any talk of it on the internet. So yeah this is a thing you can do to cut slots: put multiple hacksaw blades on a hacksaw, in a "ganged" fashion.


Then I brazed the inner cage plate in the slot of the pushrod. This is all with turbo torch and Harris Safety-Silv 56. Nothing fancy.



Then I made sure it could do the upshift. This required lengthening the slot in the tube brazed to the frame. More ganged hacksaw blades, this time held together with electrical tape. I call this tool the "Alcatraz Special". I like to reverse them so they cut when you pull instead of when you push, in this scenario. Each time you want to test the "limit screw" function, you have to remove the crank, in order to remove the derailleur. It's a huge pain!
In the end, it would do the upshift, but unfailingly shift the chain off the top. This will be solved by putting on the outer plate. So, onward!


Once I confirmed it could do the upshift, I cut the outer plate. No jigsaw this time, that thing is just a noisier version of what I can do with muscle power. The outer plate is brazed on to the inner plate and the push rod, again with Harris Safety-Silv 56.


Cleaned up and installed, and it shifts!! It actually handles the big jump from 28-48 better than anything I've experienced commercially. Maybe this is why Herse made them even though you could buy them.



All-up, this thing weighs about 180g, including the tube on the frame and the lever. So that's comparable to the lightest available cable-actuated setup with a bar-end shifter, or maybe slightly heavier than a downtube-operated one.
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Owner & co-founder, Cycles René Hubris. Unfortunately attaching questionable braze-ons to perfectly good frames since about 2015. With style.

Last edited by scarlson; 06-03-20 at 12:26 PM.
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