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Downtube lump - how to add

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Downtube lump - how to add

Old 07-06-13, 02:42 AM
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europa
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Downtube lump - how to add

First off, I'm not a frame builder and tend to dwell elsewhere on the forum, but I thought these questions were best asked here because you're the experts.

A couple of years back, I had a frame made for me out of Columbus Zona. She's fixed gear so the only cable fittings are for brakes.
I'm currently installing a Sturmey Archer S3X, three speed, fixed gear hub - that 3km cat. 4 climb I have to ride up and down every day has this ageing body complaining.
I could just use the bar end shifter that came with the hub but would prefer to use a downtube shifter. I've been able to source a clamp on, single sided shifter mount. There will be a fair bit of tension in the shifter cable so will need to find some way to stop the shifter mount creeping down the tube.

The cheap option is to put some rubber under the mount - that might even work. The better option is to fit one of those little lumps that vintage frames have for this very purpose.

I could get something brazed on but that would require some repainting which, on a pristine paint job, seems a pity. Is there an alternative?

Is there any danger of crushing the downtube by over tightening the clamp?

Zona is butted tubing. Is there any way of working out how far down the tube the thicker section of the tubing extends? The thought is that it'd be harder to crush the tubing there.

Thanks in advance.
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Old 07-06-13, 09:49 AM
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They used to make little triangles of steel to be brazed under the down tube for that purpose (wish I'd saved some from Trek), but you could easily fabricate one from a piece of scrap tubing. Yes, it would ruin the paint in the vicinity, and no, a properly-sized clamp-on lever set will not crush the tube.
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Old 07-06-13, 11:58 AM
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If you want to protect the paint, then a stop epoxied on should be strong enough - epoxy is strong enough for cable guides. I'd probably make one out of a little bit of stainless.
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Old 07-06-13, 02:33 PM
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Originally Posted by BenCooper View Post
If you want to protect the paint, then a stop epoxied on should be strong enough - epoxy is strong enough for cable guides. I'd probably make one out of a little bit of stainless.
Epoxy will not stick well to paint, you'll need to remove a bit of paint. If you chose epoxy - get the good stuff, like 3M DP460 or DP420; clean the area well with 91% Isopropyl Alcohol or other clean solvent; let the area air dry; after applying the epoxy, and clamping the part in place, let the epoxy set up at room temperature for 24 hours, then heat it up to 60C (140F) for an hour or so.
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Old 07-06-13, 08:27 PM
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Originally Posted by JohnDThompson View Post
and no, a properly-sized clamp-on lever set will not crush the tube.
Thanks for the replies.
I'm taking a bit of comfort from the quoted bit. I'll try just fitting the clamp first - should I use a bit of rubber under the clamp?
If that doesn't work, I'll go the epoxy route.
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Old 07-06-13, 08:46 PM
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The idea that putting rubber under any sort of clamp (short of a hose of some sort) is a good idea needs some serious re-thinking. No matter how much you tighten it the rubber will always give under the torsion and the clamp will be wobbly. I've actually seen some people try to use an inner tube shim in a handlebar....
You need something like a hard plastic to work as a buffer and anti-slip but there is likely always going to be a slight degree of paint damage due to clamping.
It's actually pretty hard to collapse a tube if a clamp is a good fit.
I have used a plastic strip cut from a supplement bottle as a derailleur shim.
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Old 07-06-13, 09:06 PM
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I'm not up to speed with the current crop of SA hubs and their needs. But The classic AWs didn't need too much cable tension. In fact with too much tension the plastic cable stop insert or pulley wheel would fail. Andy.
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Old 07-07-13, 12:55 AM
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Originally Posted by Andrew R Stewart View Post
I'm not up to speed with the current crop of SA hubs and their needs. But The classic AWs didn't need too much cable tension. In fact with too much tension the plastic cable stop insert or pulley wheel would fail. Andy.
I'm not up with them either. I was warned by an S3X user that the tensions were high.

Looks like I start with the clamp right onto the paint and go from there ... hoping of course that it works first time up. I'm waiting for the clamp to turn up via the world's wonderful postal systems, so there's plenty of time to worry about irrelevant stuff
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Old 07-07-13, 10:00 AM
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Originally Posted by Andrew R Stewart View Post
I'm not up to speed with the current crop of SA hubs and their needs. But The classic AWs didn't need too much cable tension. In fact with too much tension the plastic cable stop insert or pulley wheel would fail. Andy.
Originally Posted by europa View Post
I'm not up with them either. I was warned by an S3X user that the tensions were high.
Steel fulcrum clip sleeves and shift cable pulleys are available:

http://www.home.earthlink.net/~stein...erchandise.htm
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Old 07-07-13, 05:38 PM
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Back in the day Those 3 speed bikes just clamped the housing stop band around ,
usually the front of the top tube , (butt is thicker there)
And the roller at the top of the seat tube, redirected bare wire down to the hub.

Get them sized right and tight enough and they should stay Put..

... feel like belt and braces?, a Loc Tite product , (more than the threadlock stuff) may be useful ..


running cable down seatstay means you wont kick it with your heel , pedalling,

like it may be possible, using the chainstay route. .

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Old 07-07-13, 10:54 PM
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Didn't think of using the seat stay. Something to look at when I'm setting it up.

Nothing like waiting for bits to arrive in the post so you can play with them is there **impatient smilie**
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Old 07-08-13, 10:44 AM
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What shifter will you use for the downtube? are you able to mount the S/A shifter to the single side mount?
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Old 07-08-13, 07:27 PM
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Originally Posted by squirtdad View Post
What shifter will you use for the downtube? are you able to mount the S/A shifter to the single side mount?
I'm using the SA shifter. Both the bar-end and handle bar shifters come apart to bolt onto downtube mounts. The mount I'm using is a Huret but it's had a modern mount welded/brazed (dunno what) to it so it should be right.
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Old 07-09-13, 12:04 AM
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Have you considered a drill and a Rivnut?
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Old 07-09-13, 02:01 AM
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Originally Posted by Rowan View Post
Have you considered a drill and a Rivnut?
That's essentially why I'm here, to find out what my options are.
Can't say I'm keen on on drilling holes, mainly because that's unknown territory for me when it comes to working with frames. What's a Rivnut?
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Old 07-09-13, 06:09 AM
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Originally Posted by europa View Post
That's essentially why I'm here, to find out what my options are.
Can't say I'm keen on on drilling holes, mainly because that's unknown territory for me when it comes to working with frames. What's a Rivnut?
It's a nifty hardware item. It's a secret of the bike industry -- used as bottle cage braze-ons on metal frames.

http://www.rivet-nut.com/Rivnut_Fasteners.asp

I've used them in the past installing bottle cages on older frames. You don't need the special tool... a couple of dollars for the rivnunt from a bolt supplier such as Coventry Fastners in Adelaide (I used them in Tasmania, and have bought from ****ttsford Cycles in Melbourne), a piece of scrap aluminium flat bar, a drill or two of the right sizes, a centre punch and hammer, and you have a permanent fix.
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Old 07-09-13, 08:37 AM
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if you drilled your zona frame, you would be amazed at how thin the tubing is. File this one in the bad idea folder
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Old 07-09-13, 04:06 PM
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Hmmm... Machka's Marinoni was Columbus Zona with holes drilled for bidon cages.

I don't see what thinness of metal has to do with it being a bad idea. You had better explain that one.
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Old 07-09-13, 04:44 PM
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a Riv Nut , like a Poprivet ,is expanded by pulling it back to front,

in this case the threaded core itself gets pulled, outward, against its own surface shoulder.
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Old 07-09-13, 10:17 PM
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Had this descussion today at work. RivNuts like thick walls (not high grade steel wall thicknesses) and impressionable tube materials (again not good steels). Will they work, yes. For how long, depends. What you'll think when the RivNut loosens up and you can't unthread the pulley bolt, depends... Andy.
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Old 07-13-13, 08:59 AM
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Originally Posted by europa View Post
I could just use the bar end shifter that came with the hub but would prefer to use a downtube shifter. I've been able to source a clamp on, single sided shifter mount. There will be a fair bit of tension in the shifter cable so will need to find some way to stop the shifter mount creeping down the tube.

The cheap option is to put some rubber under the mount - that might even work. The better option is to fit one of those little lumps that vintage frames have for this very purpose.

I could get something brazed on but that would require some repainting which, on a pristine paint job, seems a pity. Is there an alternative?

Is there any danger of crushing the downtube by over tightening the clamp?

Or just a plain pop-rivet should do the trick. Make sure to place it specific to the clamp you are using so that it blocks the clamp.

If the clamp is the right size for the tube, then it can't crush the tube because it should close on itself at some point and not get any tighter. Tubes are almost impossible to crush from an even force applied all the way around it. The clamp would probably break or the bolt strip out first.
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Old 07-14-13, 02:47 AM
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Originally Posted by Homebrew01 View Post
Tubes are almost impossible to crush from an even force applied all the way around it.
You can crush any tube with the right amount of force, the amount of overtightened handlebar clamps i have seen leading to complete failure of the handlebar is off the hook.
For the OP, remove any kind of shims, no rubber, no plastic anything. The best connection is just the metal clamp straight onto the frame, with the right amount of tightness the clamp will not slip and will be going nowhere.
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