Lets say that I want an AL frame that does not have downtube bosses. (I like DT shifters). Lets say that I buy some steel bosses of AL threaded tubing.

Can I have the bosses friction welded to the frame?

OR

Would it be better to weld a piece of AL threaded tubing into a drilled hole in the DT and thread the shifters onto that?

If I drill through the frame would that compromise the integrity of the frame?

Couple ways to do this:
* Cannondale drilled a hole in each side of the downtube, then used a piece of threaded rod and threaded DT mounts (one side was two pieces, so it could be snugged up against the tubing). If you can find one of those mount sets (they are no longer made), you're good. Done properly, it will not compromise the integrity of the tube.
* Depending on how large the DT is, buy an old set of clamp-on DT shifters and use newer DT shifters in place of the friction ones. If the tube is too large for the clamp, you may be able to have a machine shop make a new and larger one for you.

Not a big fan of welding these mounts to the frame, but you could epoxy them if both surfaces were prepared properly.

Any welding at all on an aluminium frame will require you to have the whole frame heat-treated to avoid weakening it. Friction welding might be marginally better than TIG, but I'd imagine it will still weaken the frame to an extent, and a downtube failure at speed is probably rather unpleasant.

That aside, correct me if I'm wrong, but doesn't friction welding involve pressing the part very hard against whatever it's being welded to and spinning it very fast? Unless you had something substantial inside the frame tube, that would probably cause the tube wall to collapse, and it would be almost impossible to get something of the correct size inside the downtube of most frames.

A better idea might be clamp-on downtube shifters, although you may have trouble finding a clamp that fits the oversize tubing which most aluminium bikes are made of, let alone the non-round stuff that some of them use these days.

If you try the Cannondale mounts (my 1st choice), it would probably work best if your downtube is close to the same diameter the bosses were designed for. Chances are it's close enough, especially if you use the plastic boss instead of the metal one.

Friction welding doesn't sound doable on a tube.

Never heard of friction being hot enough to weld,
except maybe in space to earth's atmosphere re entry.

https://en.wikipedia.org/wiki/Friction_welding

Yes, I was sad enough to go and look that up. I was slightly annoyed that I wasn't sure what it was, so I looked it up to be sure I wasn't talking out of my saddle interface.

So if Cdale did it then drilling a hole and welding an AL threaded tube into the frame should be do able. My current DTs are designed for bosses so they already have a screw thread. I would just have to make sure that the tube was long enough to snug everything tight. I also would probably not hurt to thread a piece of all thread into the shaft just to give it a little more support. I was just thinking that if the market for old steel bikes ever dries up or I see a really good deal on a nice AL bike I would like to be able to do this.

Welding is not needed with the Cannondale threaded bosses.

Except they welded it pre-heat-treatment, so it was no different to welding any of the other joints.

Klein did the same thing on some of their late '90's frames. The bosses were threaded onto a double ended rod that went through two opposing small holes in the downtube. They had problems with failures and Trek (Klein's owners by then) make repair kits that replaced the damaged parts. An older Trek/Klein dealer may have one still in inventory.

Do not even think of having the bosses or anything else welded to the downtube.

What AL frames are bossless or have no shift cable stops? Just wondering-track bikes?

^^ pretty much just track frames. But then you'd have another sticky wicket trying to hack a RD hanger on. Take note, the OP has said nothing about cable stops.


If you have calipers, measure the OD of your downtube. If you don't have calipers, find someone that does and have them measure the OD of the downtube. Then get to googlin' and find a clam on pair of DT shift bosses. Pretty much your only option unless you want to monitor the area like a hawk looking for cracks.

The Cube road bike that's sometimes locked up next to mine at work doesn't, it just has standard cable stops like an MTB. I'd imagine it's because it's cheaper for the manufacturers that way.

Lots of newer frames of any material don't have downtube shifter mounting bosses which is what the OP wants. They will have dedicated cable housing stops mounted on the headtube or very high on the downtube.

Note to IthaDan: All Cannondales have large diameter downtubes, certainly much larger than the old 1-1/8" steel standard. AFAIK, neither clamp-on downtube shifters or clamp-on bosses were ever made to fit oversize tubes. Drilling small holes in the downtube to mount boses was done by both Cannondale and Klein and did not lead to tube failures so it's not a hazard or a problem.

I know it's they're oversize. A quick google pulls up clamp on bosses at sizes up to 1.5". I'm not near my cannondale frame at the moment, but that seems close to where my memory has a typical cannondale DT.

I'm just hesitant to drill anything, especially because typical DT boss location is right around where you'd hit a taper from the butt to the thinner wall in the tubing. If the frame is even butted. Just seems like a lot of potential for issue especially because I don't see anything other than a handheld drill making the hole.

What frame is it OP?

Lots of Walmart bikes are built this way, with stem shifters as well (or weird paddle shifters on the handlebars).

Myself, I would look into barcons.

Interesting. I never saw then anywhere near that diameter.

I was thinking that I could get a cheapo Scattante from performance. I would have a machine shop/welder do the drilling and welding. The DT on those are aero profile so no dice on the clamp on. I was thinking that since it is aero that a mitered tube may work, but I think the idea of drilling through and welding the tube is a better gig.

https://www.performancebike.com/bikes...chTerm=30-8268

If you look at the zoom view you see the stops. I would put the hole just right of the middle stroke of the "E". On second look the aero tube would be too wide for a miter cut.

Oh you're buying a frame?

the nashbar frame has DT shift bosses- https://www.nashbar.com/bikes/Product...2_173108_-1___

Yeah but...
At least I can ride the Performance thing and see if the AL is a good AL and not one that will rattle my teeth out. This will be my commuter and I do not use brifters. They are too expensive to replace.

How about using your downtube shifters but not on your downtube?
Mount them on your brake levers with Retroshift https://retroshift.com/
or next to them with Kelly TakeOffs https://www.kellybike.com/2nd_xtra_takeoff.html

I just bought a new Motobecane Mirage from Bikesdirect. It has downtube shifters, but there are no braze-ons on the frame for them. There is simply a hole through the frame. The bosses screw together inside the frame, that's what holds them to the frame. The curvature of the washer underneath the bosses matches the curvature of the downtube so when the screw is tightened the bosses snug up against the washers, not the downtube. This system works perfectly.

I looked for bosses of this type but I didn't have any luck. The shifters on the bike are 8 speed indexed Sunrace. I was wondering if the bosses came with the shifter set (???). The Sunrace shifter sets are easy to find on the Internet. There are two kinds, clamp-on and braze-on. The most conservative approach would be to buy a clamp-on set. I believe they come in various clamp diameters for different size downtubes. The riskier approach is to buy the braze-on set and hope that the bosses are included.

The Sunrace shifters aren't expensive and they work perfectly, as good as any Shimano DT shifter that I have used. The rear shifter is indexed only, no friction option.

EDIT: I don't think I would risk buying the braze-on set for an aluminum frame. I saw no mention of varying downtube diameters so I would assume they are for standard diameter steel downtubes only. Aluminum downtubes are of greater diameter than steel.

Or bar-ends

Or that Nashbar frame for $69 !!

I like the retroshift idea. I may go with those. I wonder how they work with friction shifters instead of index? They are heavier than my current Cane creek SCr5s, but that weight will go away with a lighter frame. So it washes.

Not too big on the Kellys though.

Your shifters will work exactly the same as they do now with the retroshifts; there is no shifter mechanism in them, just a mounting boss for the shifters.