Internal cables in the twin top tubes

In and out

These are pics of my first internal cable routing foray for FULL cable housing…not just the cable inside the frame like i wrote about previously, but the housing too.  This makes more sense to me when trying to minimize water infiltrating and cable longevity. It also makes for a very clean simple looking frame.  Heavier, yes…but like most weight-related issues, there are trade-offs.

I got the inspiration from the forum’sphere (thanks to Zancanato and Wolfhound among others) and wanted to try it out for myself.  But like usual, we all adapt ideas we get to our own situation and bike’s needs so I hope to provide some further insight and feedback to other builders and customers who may want this type of cable routing on their bikes.

The holes are about 3cm long by 1cm wide and on 16mm seatstays — that looks scary taking that much out of the steel tube.  They need to be that long to be able to feed the brass tube through the narrow diameter stay. I made them as small as I could so I could just barely push it through from the back.  I didn’t pre-bend them as there’d be no use in pre-bending with such small diameter frame tubes (i tried it both ways, made no difference in outcome). It’d be a different story if I were using a larger diameter tube such as a regular 31.8 top tube.

Once I threaded the brass internal housing through, I cleaned everything up – wiping with alcohol and a clean rag – and then used brass to braze the twin top tubes to the head tube and also braze the internal housing while there.  This turned out to be the wrong brazing material to use.  Brass needs a higher temp and the thin brass internal housing melts at that temperature apparently.  I saved it by inserting a solid steel rod into the brass housing and brazing without further damage to the housing sleeve.  In hindsight, I’d use Harris 45% silver or Fillet Pro from Cycle Designs instead of brass for this kind of thing.  Silver, even these kinds, doesn’t require such a high brazing temperature as brass/bronze so wouldn’t torch the internal housing (it has a wall diameter of 0.014″!).

After getting a good fillet around the twin top tubes I moved to the seat tube plate, then stopped the torch and switched to Fillet Pro to braze the rear dropouts and the rear exit holes of the brass internal housing.  I had already tacked the entire frame so was brazing in the bike stand flipping around as needed.  There are different ideas on this but seeing some well known peeps tack before brazing the rear dropouts, I have continued to do this as well.  I use a small brush to plop in the flux as best I can inside the slotted stays/tab-style dropouts and use the brazing rod to poke more inside to get the  best coverage I can manage.  Once all fluxed I brazed these stainless sliders with the Fillet Pro (can only use silver on stainless, no brass).  I had done some practice brazing with the Fillet Pro but no stainless dropouts.  Even though it was my first time with this setup, it went really well.  I can see what is happening much better now after a couple of years of brazing.  Fillet Pro still flows a bit more like silver than brass so there’s some initial building up of a fillet inside the slotted stay but once you find it’s correct temperature range it acts a lot like brass.  Next time with large diameter stays I’d want to figure out something to stick in there to ‘block’ the silver from disappearing within, which would save some time, brazing rod…and money!  That’s the biggest issue with silver – the cost is insane.

Once brazed, I de-fluxed in the shop sink and spend a couple hours doing the last bits of filing, reaming/facing, and cleaning.  The one thing I have noticed with internal routing, at least the way I’ve done it, is that the frame has a little bit of a “resonance.”  Not the ‘ting’ you get when you flick a steel frame tube with your fingernail, but if you bump the bike with your palm — you can hear the internal housing tubes resonate (vibrate), but not rattle.  I didn’t think that would happen on this frame with the brass housing having less span between contact points (the internal brass housing hits the wall of the twin top tubes tube more than it would were it larger diameter tubing which you’d think would dull any vibration).  Having the housing inside may help dull the sound, or make it rattle, dunno yet.  Whether it bugs me on the ride…don’t know yet either.  But I’m sure some expandable foam would help dull the sound if I hate it.  I’ll report back on that one.

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