iFozz

I've recently had an idea in my head about building a bike frame that isn't welden but rather Screwed together.

I'm thinking something like aluminum profiles with custom made brackets obviously to screw them together.

you think it would lack rigidity?Y

I mean there are structures that use heavier loads than bikes that are screwed together.

JohnDThompson 

That was the process used by AlAn frames since the 1970s, so yes, it can be done.
https://classicrendezvous.com/countr...in/italy/alan/

iFozz

That looks very interesting. So were those "joints" cast?

I've been thinking to machine the joints with a 5axis cnc mill. Very similar to those bikes.

Andrew R Stewart 

IIRC Harlen Mayer, of Hi E, built a few Al frames held together with rivets and a lot of bracketry way back in the dawn of bicycling (about 1980). A very different method of joining than the screwed and/or glued versions from Vitus and Alan (and Knesis/SR from Japan a few years later). Not many were made and, if like his hubs and rims, likely suffered from the Lotus racing sickness. Make a part so light it breaks then think about adding back a smidge more

I suspect that a frame held together only by rivets would end up being fairly heavy, likely be more flexible than other joining method result in and I would suspect the long term reliability of so many stress risers in a material that is known for very rapid crack growth. Andy

masi61

There is a mechanical engineering proffessor at Cedarville University in OH who has been building a composite hardwood and aluminum bicycle. I believe that the subassemblies are anchored with machine screws. The students and the professor have road tested this design by embarking on extended bike tours. I will have to locate the article about this, when I find it I can post it here.

bulgie 

Hi-E Cosmopolitan frames were considered very light at the time, though I don't remember any numbers. They were also quite stiff due to the large diameter tubing. They were known for creaking though! Harlan just said don't worry, that's normal.

A Hi-E frame was used by Cannondale as proof of "prior art" when they were sued by Klein. Klein's patent wasn't on large diameter aluminum tubing per se, it think it was more related to the stiffness to weight ratio or some such. A dumb patent you could never defend, and indeed Klein lost the lawsuit. Prolly woulda lost even without the Hi-E frame, but the earlier frame that was as stiff and light as a Klein definitely put the last nail in that patent's coffin.

From memory. Happy to be corrected if I'm remembering any of those details wrong.

Kontact 

For decades I've been musing about this, and I think the central problem is not understanding what holds various types of joints together. Dissimilar material joints on bikes are essentially torque tubes held together by surface area.

Consider a simple wood vertical post with a horizontal 2x4 nailed to the side of it to stick out and support a hanging weight, like a planter. When the weight is applied, trying to twist the horizontal piece down, is it the strength of the nails preventing the horizontal from pivoting down? Not really. The tension of the nails is forcing the two wood surfaces together with such force that their friction cannot be overcome.

Bicycle slip joints also work like that. The brazing material or epoxy joining the lug to the tube aren't just holding the two in position, they are creating an enormous surface that distributes the shear strength of the bonding agent, so when the tubes and lugs try to twist apart it is like a thousand tiny nails connecting them.

Imagine that same slip joint lug, but instead of glue or solder it has four screws. The screws will lock together the tube and lug at those points, but the rest of the joint will essentially be loose. Inevitably, those four screws will either shear, or the thin metal tubing they are going through will tear at the holes.

The most impressive mechanical bicycle joints I have seen are on the Ritchey Break-Aways:


The top joint is essentially two seat post binders on one post. This works because seatposts are considerably thicker than frame tubing, so clamping to them doesn't cause them to compress significantly. Trying to clamp like that around frame tubing would just cause the tubing the compress and be able to swivel under load.

The bottom joint is simpler, but also relies on thick, incompressible pieces that have considerable surface area between them, clamped by a thick bracket that can't really stretch under clamping forces. If you tried to that by just flaring the ends of the steel tubes, you would have to use a much larger clamping structure to force them together and resist the tendency of the thin tubing to change shape or thickness under pressure.

Both joints still rely on bonding agents to join to the tubes.


In summary, to make tubing with wall thicknesses appropriate for bicycles work with hardware, you need to have to have relatively incompressible clamping structures to force the tubing into maximum clamped surface contact. And the problem with that is that the amount of metal necessary to accomplish this makes the frame much heavier than the basic concept of two tubes slipped together and then filled with bonding agent. The Ritchey only has two like that, so the penalty is small compared to the 14 main joints holding together a normal bike.

The closest I can think of is something like plumbing fitting that forces the tubing between a rigid inner sleeve, a split ring and an outer clamping piece that compresses it all together. Instead of a threaded outer ring you might be able to save weight by compressing the ring down with small screws.

unterhausen

I remember that Klein's suit did rely on large diameter tubing, but my memory could also be faulty. Harriet Fell (Ph.D., accomplished cyclist in her own right + married to Sheldon Brown) was in the same class as Klein where he got the fundamental ideas for his frames. She also made a frame, so they used the one she made to show prior art. I vaguely recall that another student in that class also lent their frame to the effort. I remember seeing Klein's frame at a race, it drew a big crowd.

At that time, I was trying and failing to learn enough about composites to make frames. If I had succeeded, everyone could be talking trash about me instead of Klein.
Just to show some of the challenges, in my composite class, we analyzed composites using programs we wrote and stored on punch cards. I wish I hadn't thrown away my card deck.

Trakhak

More faulty memory: I believe Bill Shook, founder of American Classic, Inc., had also built an aluminum frame, and that it was used in Cannondale's fight against Klein's ridiculously broad patent.

JohnDThompson 

Yes. One of the common failure points with AlAn frames was the cast head lugs, which sometimes split from the interference fit with the headset parts.

Yes, the Hi-E "Cosmopolitan:"
https://www.gravelcyclist.com/bicycl...-cosmopolitan/

JohnDThompson 

Yes, specifically, his patent protected the use of oversize aluminum tubing to increase the stiffness of a frame. When Trek was prototyping its bonded aluminum frame, the tube diameters and gauges were specifically chosen to emulate the stiffness of a high-end steel frame of the time, so as not to infringe on Klein's patent. We invited Klein to the factory, so he could test ride a prototype and be confident that the Trek design didn't infringe on his patent.

Trakhak

As I mentioned the last time this topic came up, our Trek rep at the time told us that their engineers had designed the bonded aluminum frame to come in well under the stiffness of the benchmark Columbus SL frame that was specified in the Klein claims. (I believe Klein's wacky patent said that any design that resulted in a frame that was more than 25% stiffer at the bottom bracket than the SL frame would be considered to represent an infringement of the patent.)

The rep said that the Trek aluminum frame came in at 20% stiffer than the Columbus frame, which was cutting it much closer than they'd meant to.

bulgie 

I wonder if it was Shook I saw win the Fitchburg (MA) Longsjo race in about '74 when I was in high school. It was a big race with all the top riders, and the guy who won was riding a frame he said he made himself (I think!). It had large diameter aluminum tubes, in gigantic, clunky lugs that fit over the already big tubes. I kinda hated it, but I was intrigued that someone could make his own bike and race on it. Three years later, I was working as a full time FB. Maybe I would have done that anyway without that moment of "inspiration"? Probably, but who knows. I never wanted to make anything that ugly though!

Ha! Just looked it up here https://en.wikipedia.org/wiki/Fitchburg_Longsjo_Classic
and yes indeed the '74 winner was Bill Shook.

How about the nerve of the Klein guy, to patent something that everyone (well, engineers anyway) already knew, and that he didn't even develop himself. There were other frames besides Gary's and Harriet's made in that MIT class; I know of at least one other but I think it was more than that. That patent should never have been issued, in the first place, but the court came to the correct decision in the end. At least some lawyers got paid, so it wasn't a total waste eh?

JohnDThompson 

Yeah. We referred to it as the "patent on gravity."

unterhausen

If Teledyne hadn't worried about downtube shifters and bb cable guides, it would have been mooted by their bikes.

I recall being offended by the patent at the time. MIT is famous for promoting stuff like that, and they had put out promotional material about the frame design class that made it to bicycle magazines. Then a few years later, there was a patent by one of the students that could have been written by taking the claims from the articles about the class that he was in. This stuff was all pretty common knowledge anyway, it's just that it wasn't particularly practical to make aluminum frames back then. And it made somewhat less sense to use steel. I think I wrote a paper about it in high school, prior to the patent.

repechage

there was another aluminum oversized tubing race bike, Shook? Built? Anyway there was an image of it leaning against a tree with commentary about two racers in a caption of an image in Competitive Cycling, the racer’s rag. The patent survived just long enough for Schwinn and a few others to pay royalties for a short while.

then Gary got sued over the name Top Gun. My brother has one of those.

rogerm3d

one of the oldest methods for joining aluminum tubes together can be seen here: Meca Dural Duralumin

Andrew R Stewart 

Can't help but note the hose clamp around the seat post...

Has the Kabuki/Bridgestone cast joint around the in place tubes method been mentioned? Andy

unterhausen

There used to be someone (in Canada maybe?) that sold parts for the screwed and glued frames. So they could be repaired. I don't think I've ever seen one apart, there must be pictures out there, right?

Dedacci used to sell glued carbon rear triangles, but the rest of the bike had to be joined in a conventional way. I feel like the the way to go is just tube on tube carbon if you want to avoid welding or brazing.

Kontact 

I don't think the "screwed" part of "screwed and glued" was keeping the bike together. A screwed only frame would just twist itself loose, sheering any rivets that are placed to prevent that happening.

Clearly, you can skip the threads and just epoxy, but the opposition - not so much.

repechage

earlier than that, second half of the 1970’s. The Cosmopolitan. He made his own cranks too. Eclectic assembly scheme.

unterhausen

I don't remember the cranks. I wanted his pedals, don't remember why I never bought any. I have thought about building cranks.

There is a story about the Cosmopolitan being so rickety that you could hear the creaking when the rider started to sprint. I assume that a strong rider didn't have to ride one very long before the bike would start cracking.