Project: Shop Made S-Bend, 22mm ROR Chainstays

[John Clay]

I'm trying to turn conventional, straight, 22mm, ROR chainstays into S-bends in order to make clearance for 60mm fenders while retaining a narrow crank tread width. My tooling, minimal and crude, is a mandrel I'm carving out of aluminum plate and sand-filled stays (my substitute for Wood's Metal). The sand is shaken to maximize density and then further compressed by tightening a bolt in the nut that's been brazed to the large end of the stay. That worked well for the reference bike you'll see in the photos farther down; I was able to make a modest and pleasing bend without reducing the cross section during the bending process. I did add a shallow crimp as a separate step. This photo shows the basic setup:

https://www.flickr.com/photos/21624415@N04/43734090741/in/dateposted-public/

I'm having some basic success with a couple of junk stays, shown here: https://www.flickr.com/photos/21624415@N04/29863587828/in/dateposted-public/

and here:

https://www.flickr.com/photos/21624415@N04/43686800212/in/dateposted-public/

The reference bike in the photo is my 650b x 42 with 50mm fenders.

I have to work the metal hot. The skinny/crimped part of the stay in the photos is an artifact of some previous experiments and won't be part of the final product.

Going forward: I'll reduce the bending radius today and try to refine the locations and amount of each of the two bends before any more experiments. I'll add some sort of pointer or stop to the mandrel to terminate the bending operation repeatably. I'll also need to make an additional mandrel, or perhaps use my fork blade mandrel, for the third bend farther aft, to clear the crank end.

It's crude stuff I'm using, and doing, but a Di Acro isn't the budget and would need some custom, variable cross-section dies if I planned to omit the sand fill. I've seen some relatively inexpensive tubing benders but I don't recall them having dies as small as 22mm. Let me know of you know of some.

I think that ultimately this is a workable approach. I know it can be made to work in terms of fit; the trick is achieving the fit AND looking good! That's more difficult.

Any ideas? Some of you have undoubtedly tried this sort of thing. How do you go about it?

Thanks much,

John Clay

Tallahassee, FL

[Alex Meade]

John,

I’ve managed to achieve tight bends in round (not ROR) chainstays using bending dies made for the purpose, with no filling or heating. Example here:

http://alexmeade.com/photos/styled-6/photos-2/files/page2-1006-full.html

I suspect if I’d filled with CerroBend I could have spent far less time making the dies and followers.

And of course don’t try bending heat treated stays!

These days there are so many options in
pre-bent stays (including KVA who will happily do custom bends using “real” hydraulic dies), that I find I can largely happily avoid bending my own.

Alex
Http://www.alexmeade.com/Tools.htm

[satanas]

Looks good, John. ;-)

If you haven't looked at Ceeway in the UK, aka framebuilding.com, it might be worth doing so. Peter has a few S-bend stays, both Columbus (listed in the Columbus catalog posted on the site; there are drawings somewhere), and Deda; the Deda stays and a new Columbus disc stay are here:

http://www.framebuilding.com/what.htm

Peter is helpful, and seems to be able to special order any Columbus tube within a few weeks.

Later,
Stephen

[Hahn Rossman]

Thanks John. I'm pretty sure we will offer those stays through compass at some point. 

If you are used to AutoCAD you should really download fusion360! It's free for start ups, artists, students, or businesses making less than 100k a year. 

On Tue, Jul 31, 2018, 06:40 John Clay <nice.c...@gmail.com> wrote:

Thanks Hahn!

That's some impressive work you've done! I remember seeing it back when you first posted it. I'm limited to flint and stone axes by comparison. I've always bent or filed the BB spigots to accommodate a larger included angle, too. I managed to make a mandrel that does a nice job for a 42mm tire + 50 mm fender but it's not as slick as yours. I bent those stays cold and then added a small dent.

https://www.flickr.com/photos/21624415@N04/30622213552/in/album-72157674615273680/

I'm using the same approach with these S-bend attempts. Progress, but still a long way to go. I reshaped the mandrel yesterday. Now I need to get someone with a TIG machine to fill the voids so I can final shape. https://www.flickr.com/photos/21624415@N04/43034409404/in/dateposted-public/

Agree. A full scale drawing is key. Very little room for manoeuvring. Now that I'm retired I don't have access to ACAD or a decent printer so I have to use paper/cardboard! I use QCAD occasionally but for other stuff.

With your capabilities, you might make a few dies and start offering accurately bent stays for sale!

Cheers,

John

On Mon, Jul 30, 2018 at 9:00 AM, Hahn Rossman <ha...@alkifoundry.com> wrote:

Nice work John! 

I used to dent stays for clearance and got a wild hair to make the magical ROR and curved stay. 

I ended up modeling what I thought I needed in fusion 360 plus some spring back and then machining matching dies.

I didn't bother with an initial bend to flare the stays out, instead I modified the bottom bracket shell to have more angle. Some of that depends on how long your target stay is.

I think that a full scale drawing is the only way to realize how little space there is for all those things to cohabitate. 

Hahn Rossman

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John

[John Clay]

Thanks Stephen. Lotta elbow grease in that....and a lot more before usable S-bend stays come out of it!

I'll double check but I haven't seen any 22mm ROR, or round, chainstays with an S-bend. Most of my framebuilding material has come from Ceeway over the years. Peter's got the largest selection I've ever seen. Lately I tend to get tubes stateside though. Good to know about getting special orders.

[John Clay]

At the 42mm tire + 50mm fender end of the spectrum, here is the photo Cliff's notes version of what a bunch of sweat, files, sand filling & compressing within the stay (Woods Metal substitute) and a bandsaw/hacksaw/sawzall was able to produce:

https://www.flickr.com/photos/21624415@N04/30622217472/in/album-72157674615273680/
https://www.flickr.com/photos/21624415@N04/30622221612/in/album-72157674615273680/
https://www.flickr.com/photos/21624415@N04/30674797256/in/album-72157674615273680/

I managed to file a waist in the mandrel to accommodate the oval part of the stay.

But now I'm building to the Rat Trap Pass tire and 60mm fenders. That is a much more formidable challenge, hence my attempts at an S-bend coming out of the BB shell. If you look at old balloon tire bikes, or early MTBs, you'll see that they used the same approach. As those who have tried it know, being able to reliably produce the bend, of the proper offset and shape, and which looks professional, is not easy. The more rudimentary the tools, the more challenging the task!

Or maybe just trim the fender, like they did in the old days for the balloon tire bikes? But that would be too easy.

John

[John Clay]

Hey Alex,

Thanks for that information. Those are good looking bends! It would be wonderful to have proper bending equipment. I'll tell you this; making bending mandrels by hand from aluminum stock is labor intensive and slow.

I'll take a look at the KVA folks; they're new to me.

Best,
John

[Eric Keller]

This problem gets a lot easier if you use a fillet brazed bb shell.  I know that's just capitulation, but just about nobody looks at the bb shell anyway.  I have heard of an s-bend columbus stay that works with a lugged bb shell, but I have never seen it.  Seems to me that all of the bent ones are meant to work with a lugless shell, but maybe I'm just having a failure of imagination.  

The Compass bb shell is nice, but I would rather not have to bend stays. And I have a Diacro.

Eric Keller

Boalsburg, Pennsylvaia

--

[satanas]

^ Ceeway stocks both S-bend 30x16 Columbus stays and shells to match. It's also possible to order 22.2 S-bend Columbus chainstays, though some tweaking of angles may well be needed. These should fit the Compass shells, amongst others.

Later,
Stephen

[Chauncey]

Joe B and Richard Sachs sells them as well.
C

[Eric Keller]

Anyone know a columbus part number for an S bend stay that fits in a bb shell?  I tried to convince Lon to put that on his web page, but they never changed it. And I can't decipher that info from the Columbus catalog either.

[Alex Meade]

Eric,  

I've used Columbus S-bend 30x16 chainstays with standard road shells many times.  I've attached an example (although this is Columbus XCr which has a 5 degree/5 degree S-bend, a bit less than the standard road bend).  Of course you'll need to  "massage" the chainstay ports.  Up to 50mm tires seems to be no problem with lugged construction and standard road BB shells.  Fatbikes are another animal, but AFAIK there aren't any lugged shells wide enough anyway.

Alex

http://www.alexmeade.com/Tools.htm

[John Clay]

I looked in the Columbus catalog and I don't see anything like the pattern I'm trying to create. I haven't found it anywhere else either. Have I missed something?

Thanks,
John

[Jason Henkle]

There are these triple bend columbus chainstays.  They will work with a lugged shell with the requisite massaging of the sockets.  They are oval though, so not what John is after, but maybe what Eric was wondering about?

https://framebuildersupply.com/collections/chain-stays/products/columbus-zona-29er-triple-bend-chainstays-oval-round-24-od-9-wall-length-470

-Jason

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[John Clay]

My bending mandrel is back from getting some voids filled where I removed too much metal during the rough-in phase of the two new, small radius corners. The voids allowed the ID of the test stays to buckle; they were bent hot.

This is the original side of the mandrel.
https://www.flickr.com/photos/21624415@N04/43919978132/in/dateposted-public/
It, along with a small dent, produced these stays, cold bent: https://www.flickr.com/photos/21624415@N04/30702037516/in/album-72157674615273680/
The results are excellent for a 42mm wide tire with fenders. I can get plenty of room for a 50mm wide tire, like the RTP, too but I don't think it would be adequate for 60 mm fenders without denting them (which is fine but I'd rather avoid it if I can while ticking the other boxes).

This is the opposite edge. I made two forms of much smaller radius on each corner and hogged out too much material. 
https://www.flickr.com/photos/21624415@N04/43249939974/in/dateposted-public/
I'm hoping to be able to produce an S-bend with one or both of these corners. I'm also considering a properly shaped hold-down die for the end of the tube (rather than a steel strap, and a roller on a lever patterned after proper tubing benders. Not sure if I'll go to the trouble and I certainly won't before trying to bend some test material hot and sand filled, freehand, but I'm thinking about it.

John

[Jason Henkle]

Out of curiosity is bending bicycle tubing hot common practice?  Anyone know much about the metallurgy?  John, I've enjoyed getting a peek at your thoughtful process.  Thanks much.

-Jason

--

[M-gineering]

On 8/11/2018 12:07 AM, Jason Henkle wrote:
> Out of curiosity is bending bicycle tubing hot common practice?  Anyone
> know much about the metallurgy?  John, I've enjoyed getting a peek at
> your thoughtful process.  Thanks much.
>

If you're heating the opposite side of a brake bridge you're already
bending hot, but more commonly it is done when you lack the tooling, ie
old timers of making a one -off. The Rih docu on You-tube shows
forkblades being bent.
Don't do it with heat treated tubing though

--
mvg

Marten Gerritsen
Kiel Windeweer
Netherlands

[Jon Norstog]

What Marten says.  I heat-bend chainstays from aircraft tubing, usually .035" or .028" (.9/.7 mm) wall thickness.  Aircraft tubing is mildly heat treated - they call it "normalized" - and the bending process wipes that out.  Post-bend the tube is very ductile in the heated area, but still has the same modulus of elasticity.

I had a shop make up a hundred 7/8" x .035" chainstay blanks with a 30-degree, 3-inch radius bend at one end.  The shop annealed the tubes in order to make a clean bend.

jn

[Jason Henkle]

Interesting, thanks for the replies folks!  Sorry for the thread drift as well!  Back to John's bending progress...

[Hahn Rossman]

It was all brazed. I just threaded thru the wheels frame etc when it went in the box for the plane. I would do it that way again and think compromising the 99.9% use for the .01% is a bad idea. 

You can always make another rack if in the future you really need a demountable one.

Hahn

On Tue, Aug 14, 2018 at 3:30 AM John Clay <nice.c...@gmail.com> wrote:

Hahn!

Did you braze the front/ struts to the porteur rack you used in Mexico, or were they detachable? I'm trying to decide whether to go to the trouble of making them detachable, a la Alex Wetmore's approach (he told me that his tabbed connections resulted in a flexible rack mounting) or just braze the things on (I do like expedient and simple). There's no population of like minded riders/tinkerers experimenting with this stuff down in these parts! Other ideas?

The likelihood of this bike taking an airline flight is somewhat small but not zero. I'm curious to know your approach and experience on this.

Thanks much,

John

On Mon, Jul 30, 2018 at 9:00 AM, Hahn Rossman <ha...@alkifoundry.com> wrote:

Nice work John! 

I used to dent stays for clearance and got a wild hair to make the magical ROR and curved stay. 

I ended up modeling what I thought I needed in fusion 360 plus some spring back and then machining matching dies.

I didn't bother with an initial bend to flare the stays out, instead I modified the bottom bracket shell to have more angle. Some of that depends on how long your target stay is.

I think that a full scale drawing is the only way to realize how little space there is for all those things to cohabitate. 

Hahn Rossman

On Mon, Jul 30, 2018, 07:35 John Clay <nice.c...@gmail.com> wrote:

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[John Clay]

Thank you. I am glad to hear it. About 3 hours ago I came to the exact same conclusion and made the front stays. I was about to tack them to the platform when I realized that I needed to add the headlight mounting arm to one and drill/configure it and the stay for internal wiring! Remembered just in time.

John

[John Clay]

On the chainstays: The 650b x 42 (BSP) frame I recently finished has a single bend, loses little of the original ovalization and has a 57mm wide space for the fender and tire. Crank tread is 136mm. I took another look this evening and with the same type of single bend, but just going a little further, getting enough room for a 60mm fender while maintaining the 136 Q won't be a problem for the Rat Trap Pass frame I'm building. There is adequate clearance to knock at least 4mm off the Q of the BSP bike with a shorter spindle but the RTP will have a 135mm rear hub it will probably end up about 140 unless I recurve the aft portion of the stays.

I'll probably still see if I can make a serviceable S-bend on some round tube stock but my guess is that I'll end up using the same single bend approach of the BSP frame.

John