32

tl;dr heating chromoly to brass-brazing temperature doesn't really change it, at all; the steel was born hot and heating it back up does nothing to it other than oxidizing the surface if you don't protect it with flux. For special proprietary exotic steel tubes heating them up may or may hurt or it may help; there is no rule. There is much wrong, and not-...


17

When you consider the overall outcome - the final bike, not just the frame, hand building in aluminum rarely makes sense. Modern aluminum factory frames are hydro formed into all sorts of engineered shapes that save weight and provide stiffness and compliance where needed. There is no way to hand build an aluminum frame even close to the characteristics of a ...


14

I would not. Instead I'd strongly recommend you look at buying the bike you want rather than chopping up a working vintage bike. At best you'll come out with something worse than a replacement aluminium road bike, and perhaps slightly better or worse than the bike with which you started. A used 2000's bike would be a far better bike than some chopped-up ...


14

I'd go with full housing for both brake and gear cables and hold the cables on with cable clamps. There are many kinds of cable clamps to choose from. I prefer the type that have a screw clamp over the clip on type. The key will be finding clamps for your tubing diameter. If you need to have cable stops there are clamp on versions from a variety of vendors....


13

Interesting question and way of looking at it. Here's my take: those in the bike world who would seem most qualified to design scientifically optimal frames, which involves both mastery of all the advanced fabrication techniques and materials that are now available and the motivation to empirically figure out the handling and ride feel elements that can be ...


11

3D printing have many disadvantages: Materials cost and strength: although new materials has been made over the years to reduce the cost, it is still quite expensive for mass production. In our department, a good material would cost £10/g, and the cheapest is around £1/g (very porous and fragile). Labour cost: it takes time to CAD a small part, but it takes ...


10

There is a lot more to a bike frame than just weight. If there is one thing early aluminum frames taught us is that straight gauge aluminum rides harsh! Modern aluminum frames typically employ hydroforming to tailor the compliance and ride characteristics of the frame. This is why modern aluminum bikes ride a lot better than 90’s aluminum frames which were ...


9

The reason that brazing is traditionally used on steel bikes is so that the temper of the chromoly tubes won't be wrecked. (The high temperatures associated with conventional welding would seriously damage the tubing.) However, Cannondale, in their push to develop good aluminum bikes, invented the technique of rapid welding (since aluminum can't be brazed, ...


9

Unless you are of extremely uncommon proportions, you won't find much riding advantage in a custom-made bike— there's plenty of room to tweak a mass-production bike for the a perfect fit through component swaps. Moreover, unless you buy from an experienced touring-bike specialist, it's entirely possible that a custom-designed bike might have little ...


8

You're almost certainly better off spending that money on going touring. I'd go so far as to say that until you have done enough touring to have a list of things that you want from your touring bike that you can't get from any production bike, don't bother thinking about it. Well, unless your other hobby is spending money, in which case I suggest buying one ...


6

I remember seeing courses about how to make a bike frame, but they were not about new designs, they used standard designs and the courses were about selection of tube, welding/brazing, finishing, etc. Perhaps you start by learning to braze, then building a "conventional" lugged steel frame, then develop that based on what you learn in the process. This ...


5

While you probably could cold set it, the Sturmey-Archer XRF-8 is available in a version with 120mm OLN dimension. (And you almost certainly can fit a modern bottom bracket. Worst case, have the existing threads removed and fit a threadless bracket. Bottom bracket size guide.)


5

I suggest starting with a prototype made out of square tube and old bikes, especially if this is your first framebuilding project. Square tubing is a bit easier to work with (you spend less time mitring tubes) and the goal for the prototype is that it should be easy to build. Take shortcuts, in other words. Get something you can ride, then ride it. When ...


5

This is only engineering judgement, not technical analysis: the damage does not appear particularly serious or significant at that location. As Daniel advises above, keep an eye on it for cracks developing. If you are just a "normal" everyday type user it could be OK for quite a while. The Al frame will eventually crack and fail, not necessarily at this ...


4

The only real advantage to a compact geometry road bike is for the manufacturers. Since standover- which is the distance from the top tube to your crotch when you straddle the bike with your feet on the ground- is increased, one size of frame will fit a wider height range of people and therefore the manufacturer does not have to make as many different frame ...


4

As far as I know, nowadays most bikes (not the extra cheap neither the extra fancy) are TIG welded. If I'm not mistaken, MIG is used for lower end aluminum frames. I have made a lot of hacks and fixes to steel frames (including building a recumbent frame from an old, already cracked, MTB frame), and always used TIG weld, with excelent results, either ...


4

It should be possible to repair the frame, the big question is whether you'll be able to find a replacement tube or will you have to make it yourself. Making the tube isn't hard, it's just messy. The repair will involve cutting out the damaged tube, working out what else (if anything) is damaged, and paying careful attention to the other tubes. Then once ...


4

You can't build any bike with minimal effort. Not even a toy one out of Lego. It would be faster and easier to get a minimum-wage job and save money to buy a commercially made bamboo bike. But a lot less interesting, and also less fun. Turning bamboo into something suitable for a bike frame is quite a lot of work, and if you haven't worked with structural ...


3

Mattnz's answer is canonical and addresses aluminum, steel, and titanium frames. Until we can easily 3d print metal frames, custom frames are going to be tube based. Hydroforming metal for one-off bikes isn't worth it and you can't easily braze aluminum (you have to TIG weld it). But this leaves out another important material (as Chris H notes): carbon ...


3

the step-through height must be no higher than the top of the pedal stroke, since the rider will need to have their foot that high to ride the bike. The exception, obviously, is bikes for people who can't lift that high but can accept forced motion that high. But those are generally built for rehabilitation rather than primarily for transport, like the one ...


3

I'd avoid doing this. Basically, you do a light (typically wet) sanding by hand (very carefully), prime it with an appropriate primer (maybe a few times) and then paint over it with an appropriate color. However, since the sanding has to be done carefully (since its easy to destroy carbon fiber by sanding), you're going to end up paying someone a lot of ...


3

At first I read you to mean an off-center wheel plane, but not so. Interesting question, i.e. does a bike remain stable/rideable if rear axle is not symetrical? I guess yes, as long as front/rear wheels are in line, but practical clearance issues immediately become apparent. Tolerances in modern frames and wheel-drivetrain designs already nearly max out ...


3

There has been in the past--Shimano once had aero group variants (Dura Ace AX and 600 AX), which included an aero-section seatpost. I had a bike that came with one such seatpost. Unfortunately the binder clamp on the seat tube didn't quite keep the seatpost in place, and I had to have a framebuilder tap a hole for a setscrew.


3

I think your question is basically, "Is it possible to build a frame out of different parts?". The answer is yes, because frames exist in the market, and most of them are built of different parts, so it's definitely possible to build them. On the other hand, a bike frame being something that can get you killed if it suddenly fails, I most definitely would ...


3

If I'm describing a complete bike, it's defined by wherever the center of cogs are at that time. As we move into this bold world of full suspension mountain bikes with adjustable geometry, the ones with flip chips on the dropouts talk about the varying lengths of the chainstays. Santa Cruz's description of their Megatower frame (emphasis mine) In order ...


3

Here is a nice clear picture of the basic joint used in constructing things from their website. There is a washer on both sides. Their bill of materials calls for stainless bolts, stainless washers and stainless self-locking nuts: B O L T S & N U T S M6 SELFLOCKING NUTS, stainless (DIN985) - ca. 150 pieces (TWOSEATER: 200 pieces) M8 SELFLOCKING NUTS, ...


2

Q: You generally see the top tube on steel bikes being parallel to the ground, whereas on a lot of carbon bikes it's angled. Why is that? A: It is because most steel bikes you see are old, designed and built in an age before the sloping top-tube was conceived (for Giant bicycles by Mick Burrows in the mid-90's I believe). So aside from recent artisan-built ...


2

I am an old-school welder, whose first job was torch welding tool steel. So I am going to braze my frame. I love both other processes and would TIG if I had one. My reasons for choosing brazing are twofold. Bronze is not as brittle as steel or moly so it doesn't fatigue as fast. Second, even perfect MIG and TIG welds concentrate the heat to such a small ...


2

As a builder of home bicycling contraptions myself (recumbents not bicycles) but also as a nationally competitive TT'ist (seniors) I have a comment on centering. Of course making the spoke offset symmetrical would (as mentioned prior) push the cogset far out, perhaps in 35-40mm range (just a rough guess). To keep the chain line correct would force the ...


2

Sure, anything is possible, especially if you have access to a oxy-gas welding or brazing torch (or arc/MIG/TIG welder), a grinder with a cut-off wheel and a willingness to cause mayhem. As a BMX, it'll be heavy and ungainly, especially around corners. When you pedal, it'll pull to one side as it doesn't have a differential, but it'll be tons of fun and ...


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