What's the strongest way to bond a cable stop to an aluminum frame?

Question

I recently picked up another well loved GT road bike frame- it's in great shape aside from a missing downtube cable stop. The model is a ZR 4000 probably from 1999, it's 7005 heat treated aluminum. My best guess is that the cable stop was originally glued or bonded to the frame somehow based on a lack TIG weld lines or braze. I'm not sure if the cable stop snapped off from poor storage or when the frame was in use last. It's a CL find and lived in a garage for a number of years.

What's the best way to reattach a new downtube stop? Would I have a stronger bond if the new cable stop was aluminum or plastic? I have a great work space with appropriate ventilation and equipment, but after preliminary research I've found a lot of aluminum specific products (like those used on airplanes) can't be purchased online or by individuals, so whatever product needs to be accessible in that regard.

I'm also open to non-adhesive/epoxy solutions, but the tubing is ovalized and very oversized, so using downtube shifter clamps doesn't seem feasible. As a last resort, would using a hose clamp be safe on ovalized, aluminum tubing once I got it tight enough to withstand the forces of shifting? As a last, last resort, I am prepared to run cable housing all the way from the brifter to the cable guides under the bottom bracket. I'd like a pretty bike, but ultimately this one is just for riding and not show.

Answer 1

Since you have a relatively "flat" spot there (at least flat in the longitudinal direction) you have two options:

1. You can epoxy on a replacement boss

I did this on a recent Al frame with the exact same problem. I bought a metal (steel) cable boss from the local bike builder and epoxied it myself. I used Loctite's Metal/Concrete epoxy since it's designed for:

machinery, appliances, tools, lawnmowers, automotive components, pipes, embedding bolts and screws into metals, concrete or stone and sealing electrical components against moisture and vibration

Although lots of other epoxies will probably work.

If you do this be sure to read the instructions on the epoxy, clean the surfaces on both parts, and create a good clamp for the piece. It'll take 24 hours to dry fully and you aren't going to achieve good results by holding it with your hands.

Once's it's dried be sure to test it by attaching whatever brake/derailleur the boss is for(in your case the rear derailleur) and running cable through it. You need to be sure that the epoxy will hold the forces that will actually be applied by the brake/derailleur** Don't expect your results to look pretty though.

2. you can rivet on an replacement boss

There are many options here depending on what type of cable stop you need.

You could easily do this your self but you'll likely end up with a rivet gun and a box of 100 rivets you'll never use again (on a bike at least).

Whatever method you chose, I'd suggest completing it before any of the rest of your bike build (I'm guessing from the missing front end that you're rebuilding this bike). If you can't get it fixed you might have to scrap (or at least rethink) the project and you don't want to waste any money on other parts until you know for sure.

Regarding welding:

Aside from the heat issue of welding aluminum, you'll also have a tough (impossible?) time finding someone who can weld a steel boss onto an aluminum frame. Or you'll have an impossible task of finding an aluminum boss to use instead. Think about it.. there's a reason the manufacture glued the boss on in the first place.

** Be extra careful if you are repairing a brake boss. It holds more force and obviously has more dire consequences if it breaks off again.

Answer 2

Good epoxy is known to bond metals, especially aluminum very well. Make sure the surfaces are clean and slightly rough for a better bond. I use the same two part epoxy hobbyist aircraft builders use for fixing pretty much anything, including broken ceramic mugs, small broken metal things and even as an insulator on the bottom of PCBs to prevent any shorts.
When looking for replacement cable stops try to get something with a solid base and not hollow so you can glue the whole thing down. From the looks of it the original was only glues around the edge which is probably why it came of.
Another solution could be solder. It will be stronger but look a little asymmetrical, but as long as you do it to the other cable stop too it should look fine. It melts at a low enough temperature for nothing to happen to the heat treatment of the aluminum. I take no responsibility for the frame if you do this however, it's only my guess, and is completely untested. Would like some input by someone who knows a little more about solder and hest treated aluminum about this solution, it seems workable

Answer 3

If you have a 3D printer, you can design cable stops that fit your frame and print them. This is one I made:

I have been using this version for a few years now and didn't have any problems with it.

It is printed with PLA. For the 3D modeling I used TINKERCAD.

If you are interested in the model files, you can get them from thingiverse here. The diameter of my frame is 27 mm in the front and 16 mm in the back at the places where the cable stops are attached.

Answer 4

I tried epoxying the frame stop onto the frame, and took utmost care but front deraileur cable stop came off.

Now I am considering this "On Frame Cable Stop, Alloy Double, 31.8mm , Black" instead.

Answer 5

I have the same problem with a downtube that is 38.7 mm in diameter and I cannot find anything suitable ready made.
So I made my own and it works.

Word of warning, this is only for shifting gears and not for brake cables. Don't risk your safety with this type of hack.

OK now I call this prototype 1 and this is what I did, parts list:

1. A hand full of stainless steel Nutsert like this one: https://www.boltandnut.com.au/m6-x-1-00p-metric-coarse-0-5-3mm-grip-g304-stainless-countersunk-smooth-closed-riv-nut-nutserts
2. A bag of Stainless steel cable ties 7.8 mm wide and at least 250mm long, something like this: https://www.bunnings.com.au/deta-7-9-x-250mm-316-grade-stainless-steel-cable-ties-10-pack_p0381121
3. Purchase a short length stainless steel chain like this but you need to make sure that the nutsert seats on a chain link leaving space for the cable ties to slip through the sides. You only need one chain-link. https://www.bunnings.com.au/pinnacle-3mm-1-8-x-1m-stainless-steel-chain_p0358129?region_id=118164&gclid=EAIaIQobChMI3-_1_pTmgAMVdt0WBR0mCAPWEAQYASABEgJ-S_D_BwE&gclsrc=aw.ds
4. Alcohol to clean your parts before gluing
5. Epoxy glue. Turn the assembled nutsert upside-down to pour glue into the link and nutsert, use blue tack to seal gaps between the nutsert and the chain link so the glue does not leak out.
6. Metal drill bits, 6mm drill to remove the thread inside the nutsert and a 3 or 3.5mm to drill a hole for the cable. Don't use 2.5 mm drill bit like the one in the part list photo, it's too small and the drill bit is fragile. Make sure the drill bits are Cobalt tips. This is a picture of the list above Now assemble it like this:

Some tips:

1. Make more than one, the zip ties are one-way and if something goes wrong when installing on the bike, then you have a spare one to try again.
2. Cut a thin piece of card paper to make a strip that is the same width as your cable ties and run it around the nutsert, chain link and use sticky-tape to hold it together and install it on your bike tube as a prototype and with a pencil mark in the strip where you want thing to be: the nutsert, zip/backle and the existing cable stop in your downtube, if you have one. Use the strip as a guide when you assemble the nutsert.
3. Use Electrical tape or Polypipe between the cable tie and your bike tube, to protect the bike paint work. Make sure you have plenty of width so that your nutsert and chain link seat evenly on the bike tube.
4. Drill the the 3 mm hole first and do it from the inside of the nutsert, it will self-centre, mine do anyway, because its bottom is conical-shaped during manufacture when the thread is cut in the nutsert. Then drill out the thread with the 6 mm drill bit, this will make enough space for your bike cable and at the same time it will clean any sharp edges from the 3 mm whole inside the nutsert. Use the 6 mm drill bit to clean any sharp edges from the 3mm whole outside the nutsert.
5. If you are installing it next to an existing cable stop, if you have space in your downtube, install it in front of the existing one. This will stop your installed cable-tie from slipping down the bike tube pass the existing cable stop.
6. User pliers to pull the cable tie tight and then fold-it over the zip/buckle and hold it in place with a trigger clamp and if you can push it into a hand-made tie-loops, like the ones you see in the pictures and be careful not to use anything stronger than a trigger clamp and then with a toothpick or bamboo skewer, put epoxy glue inside the exposed buckle gap.
7. If the cable tie stretches and becomes loose, get some plastic spacers from the hardware shop, they look like small wedges, and with a piece of wood and hammer gently tap it in between the cable tie and the polypide.

I am building prototype 2 and yes, I am also building a cable tie tensioning tool with it.

Now, what shall we call this? A "Saddled Nutsert", "Saddled RivNut"?

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Cable Tie Tensioning tool

Hi, This is the second part of this answer where you need a tensioning tool for the Stainless Steel cable tie. What you need:

1. Door Hinge, with a loose pin and approx. size 100mm like this one https://www.bunnings.com.au/pinnacle-100mm-single-loose-pin-butt-hinge_p0074272

2. A small packet of High tensile bolt/nuts M6 preferably 100mm long thread running right through like this one (make sure is M6 otherwise it wont fit in your door hinge): https://www.bunnings.com.au/pinnacle-8-x-75mm-yellow-zinc-hi-tensile-hex-bolt-and-nut-4-pack_p0054202

3. Hacksaw or better yet Angle Grinder

4. Flat metal file

5. Metal screws with square nuts or what ever you have at hand

6. Washers

7. Metal bracket

Now assemble it like this:

The washers are between the metal plates to let the cable tie slide between both plates [![Use sticky tape to help it stay in place while you rotate the boss counter clockwise with a ratchet socket][12]][12]

Some advise: The door hinge tool, is small and allows you to position the cable tie buckle at the top of the tube circumference and allows you to fold the tie over the buckle easily within a confined place.

Some tips for assembly:

If you are right handed, put the head of the bolt holding the boss on the right hand of the hinge. Make sure the boss is in the right direction as you turn it counterclockwise to put tension on the cable tie.

If you are right handed, work from the left side of your bicycle frame so that you reduce the chances of you ratchet or spanner heating your bike and scratching it.

To protect your bicycle paint, wrap the edges of the tensioning tool with duct tape.

Once you get the right tension and you lock the boss, turn the tensioning tool over so that you fold the cable tie over the buckle, to help secure the tension. If you don't have a second set of hands, you can use a trigger clamp to hold the cable tie over the buckle, as you loosen the boss and release the cable tie.

Other alternatives are ready made tools like this one: https://www.amazon.com.au/Pliers-Automotive-Banding-Crimper-Cutter/dp/B0CC1RHC49/ref=sr_1_4?keywords=cv%2Bstrap%2Btensioning&qid=1693312076&sr=8-4&th=1, but consider the fact that you have to fold the cable tie over the buckle and the size of this tool may only allow you to have the buckle on the side of your bicycle down tube. Consider that your cable stop is positioned in a confine place within your bike frame.

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Preview of Prototype 2

Answer 6

You can take it to a welding shop and they will be able to weld it.