# Demountable -- Homemade coupler



## Linnaeus (May 17, 2009)

I'm making a demountable to take to South America this summer for transportation and some touring. Since S&S will not sell to hobbyists, I decided to make my own coupler and use a Ritchey Break-Away style top coupler. This required moving the seat stays down. 

The coupler is a bit larger than it needs to be, but I built it around a tap that I already had (1 5/8ths x 16tpi), which was much quicker and easier than cutting internal threads on the lathe. Because it is essentially my prototype piece, I just erred on the side of safety and durability at the expense of weight with all 3 parts of the coupler. Because this is going into a low quality old steel frame, and because of the intended use of this bicycle, the weight gain is not a concern. 

I could have gone with a Rene Herse style bottom coupler (essentially a clamping sleeve) or the Ritchey Break-Away style bottom coupler, but I wanted something that was easy to assembly and would be very resistant to torsional flex. I have read on the framebuilders mailing list archive that the Ritchey style bottom coupler is extremely flexible (under objective testing), which is not surprising given its design. Although not as sexy or complex as the S&S splines, the simple "dog" style engagement should function well. 

To finish the frame, I just need to add the second seat post clamp and braze in the couplers. I may also add disc mounts if I have the time before leaving on my trip.


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## CheeseSoda (Jan 8, 2007)

Looks pretty dang snazzy to me.


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## scoutcat (Mar 30, 2008)

that looks plenty beefy to me.


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## hwilliams (Apr 26, 2009)

How do you plan on tightening the collar, are there flats or the like to get a spanner onto?
some nice machining there.


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## Schmucker (Aug 23, 2007)

Looks good and probably a hell of a lot cheaper than S&S couplers. They are such a ripoff.


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## Schmitty (Sep 7, 2008)

Love it... nice work for a 'hobbyist'. More chops than half the pros that s&s sells to.

-Schmitty-


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## pvd (Jan 4, 2006)

I'm impressed, but it looks like you forgot a provision for driving the nut.


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## jay_ntwr (Feb 15, 2008)

pvd said:


> I'm impressed, but it looks like you forgot a provision for driving the nut.


I'm guessing a stint in the indexing head will fix that. He's got enough material in the wall to turn plenty-o-flats. 15" adjustable wrench should do the trick eh?


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## nicknoxx (May 25, 2008)

Have you seen the Rohloff bayonet gear cable couplers? Might be useful
http://www.sjscycles.co.uk/product-...or-Gear-Cables-1-Male-1-Female-8274-11743.htm


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## pvd (Jan 4, 2006)

jay_ntwr said:


> I'm guessing a stint in the indexing head will fix that. He's got enough material in the wall to turn plenty-o-flats. 15" adjustable wrench should do the trick eh?


It sure would, but the parts are now welded into the frame. Timing is everything. Kinda tough to load a bike frame into a 5C collet.


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## Linnaeus (May 17, 2009)

PVD et al - you are correct, it doesn't yet have a provision for tightening the collared nut. I am going to add 3 or 4 short, blind holes that will fit a spanner wrench. I just haven't decided how accurate I want to be, and whether I should just "eyeball" it or put the indexing head on the Bridgeport. I'm leaning towards the former. The problem with milling some flats is that I don't want to lug around a big adjustable wrench in South America or when on tour. 

Schmucker - I'm not so sure the S&S are a rip off. Compared to the time I spend making these parts, I would have gladly just purchased and S&S coupler. Of course, the set-up takes a long time and the 1st one always takes the longest, but it took many, many hours to make this coupler.


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## Schmucker (Aug 23, 2007)

Still cheaper than S&S. At my current pay rate the couplers would have to take me longer than 30 hours to make to have it no longer be worthwhile.


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## Walt (Jan 23, 2004)

*Not a ripoff...*

Personally, I think the S&S couplers are a pretty decent deal for $150-ish. They are quite intricate, made from stainless, well engineered, and bombproof.

For this project, they would obviously be overkill, but for a "nice" bike, they're the way to go, IMO.

Personally, I think the ripoff is $150 each way for a non-coupled bike on most airlines!

FWIW, you can also pack Ventana full suspension frames into S&S cases. That's what I do for a travel bike.

-Walt



Schmucker said:


> Still cheaper than S&S. At my current pay rate the couplers would have to take me longer than 30 hours to make to have it no longer be worthwhile.


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## Linnaeus (May 17, 2009)

The Homebrew Demountable is done for now. I brazed in the couplers a couple days ago and threw on some quick RustOleum just to prevent corrosion (looks are not important). I built the bike by cannibalizing a couple of my other bikes, it's mostly Deore M440, 9 speed drivetrain, cheap V-brakes, and a vintage wheelset with XT front/ Hershey Ti rear hubs. 

I did have to make a shim to fit the 34.9 front derailleur to the 28.6 ST. A brass bushing was handy and had diameters that were close. I had to replace the derailleur hanger, which required cutting the old one off and welding in another one. I also reamed the ST out from 26.6 to 26.8, which made finding a long post easier. I ended up adding 3 blind holes to the coupler and have a specific spanner wrench that tighten/loosen the joint (it's visible in one of the pictures, sitting on top of the Park frame clamp). 

The frame is small compared to my other bikes (ST measures at 21" CTT), but the final fit is quite similar to some of my other bikes albeit a bit more upright. For touring, that's probably a good thing.


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