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-   -   Student Piece (http://www.bikeforums.net/framebuilders/776981-student-piece.html)

Mark Kelly 10-21-11 09:08 PM

Student Piece
 
I've been teaching myself to braze using an ordinary air propane torch and Cycle Designs System 48, Fillet Pro and White Flux.

As per a request in another thread, this is my student piece, a rack for my wife's bike:

http://bikeforums.net/attachment.php...hmentid=223991

It's made from 9.5 x 0.9 SS304 tube and a combination of home made lugs (System 48) and fillet joints (Fillet Pro). Some of the lugs are internal. The lower mounts were cut from 5 x 20 SS flat bar.

It's too heavy and not as straight as I wanted, mostly due to the poor tube bending. The two sockets on the left were for upcurved tubes to attach to the frame braze-ons. This won't work (it will foul the brakes) so I'm going to have to cut them off and use something else. Not the first such re-jig; I originally made the whole thing 50mm too tall so I had to cut the side supports and re-join them (internally lugged)

unterhausen 10-22-11 12:28 AM

that's really nice. I'd like to see it when you get it on a bike

rodar y rodar 10-22-11 07:12 PM

Wow MK, it`s beautiful! It sounds like you`re disappointed, but I hope you eventually get it to work on her bike- I`m sure you`ll feel a lot better when you see that nice stainless all mounted up and put to use. Did you bend the tubing around a curved block? I`m generally not a fan of curvy stuff, but the circles and limted curves in your design really look nice.

EDIT: I just noticed that the main body of the rack is one continuous loop. No wonder you had a hard time keeping it straight! Getting all those U- bends equal to each other has got to be a bear, even if you`re doing them in sections and butting together.

Mark Kelly 10-24-11 12:53 AM

Quote:

Originally Posted by unterhausen (Post 13398538)
that's really nice. I'd like to see it when you get it on a bike

http://bikeforums.net/attachment.php...hmentid=224282

Here you go.

I had to cut off the sockets and work out a new way to attach the rack to the frame mounts. As usual I chose a method which was unnecessarily difficult but offered the chance to learn new stuff.

I cut two semicircular notches in each of two pieces of SS rod so they fitted between the two tubes at the front, brazed the rods as inserts into a couple of short pieces of tube and fillet brazed the whole thing as couple of T joints off the front of the rack. I then used another couple of pieces of rod at the other end as mounting eyelets.

Alan Edwards 10-30-11 10:46 PM

Great job, if your practicing to build a frame I think you are there.

Mark Kelly 10-31-11 01:21 AM

Thanks for the vote of confidence, but I know I'm not there yet.

Next cab off the rank is replacing the chainstays on my son's frame (I managed to damage one when cold setting it from 126 to 130 mm).

After that there's a bunch of practice with the tube joining technique I'm developing which is aimed at optimising the acoustic properties of the frame. I'm making life difficult for myself - none of lugs, welds nor fillet brazing will suffice to achieve what I'm aiming for.

Sixty Fiver 10-31-11 01:46 AM

Quote:

Originally Posted by Mark Kelly (Post 13433273)
Thanks for the vote of confidence, but I know I'm not there yet.

Next cab off the rank is replacing the chainstays on my son's frame (I managed to damage one when cold setting it from 126 to 130 mm).

After that there's a bunch of practice with the tube joining technique I'm developing which is aimed at optimising the acoustic properties of the frame. I'm making life difficult for myself - none of lugs, welds nor fillet brazing will suffice to achieve what I'm aiming for.

The design of the rack is very pleasing and I understand how much work building a rack is... my partner, who has been building frames for 30 years says racks are almost as much work as building a frame.

I can understand replacing chainstays but what are these acoustic properties you speak of ?

I ride bicycles, I don't play them.

:)

Mark Kelly 10-31-11 02:03 AM

I've been working for a couple of years on a pet theory which is that what we call "ride quality" is chiefly an acoustic phenomenon. What we want is a frame which transmits road feel (the signal) without adding extra harshness (noise). The analogy is to a signal to noise problem in audio design and since this is a field in which I have some background, I started looking at ways of working with this.

My biggest experiment so far was to have a custom titanium frame built (I don't have any experience welding Ti) and grind chunks off it in a pattern which I hoped would modify its acoustic properties. This worked quite well (better than I had dared expect) but I ended up deciding that I could probably achieve more with steel and at lower cost. The experiments I've done so far are encouraging, it just looks like I'm wrong about the "lower cost" bit.

rodar y rodar 10-31-11 02:32 AM

Quote:

Originally Posted by Mark Kelly (Post 13433311)
My biggest experiment so far was to have a custom custom titanium frame built (I don't have any experience welding Ti) and grind chunks off it in a pattern which I hoped would modify its acoustic properties.

:eek: Yowza!

Mark Kelly 10-31-11 03:02 AM

Quote:

Originally Posted by rodar y rodar (Post 13433339)
:eek: Yowza!

Yeah well, I really wanted to find out what would happen and I was reasonably careful* with the procedure. I'm still riding that frame and it hasn't busted yet, if it does I'll chalk it up to experimentation (as long as it doesn't break too many bits of me).

* I invested in a decent quality echo / echo ultrasonic thickness gauge and used it to determine the amount of Ti to grind off. I went to a minimal thickness of 0.55 mm and I know that Darren Baum has gone as low as 0.4mm on some of his "show" Ti frames so I reckon I'm reasonably safe. Darren is just up the road from me and as usual he was incredibly generous with his time and knowledge when I bugged him for information which could help me.

Scooper 10-31-11 08:06 AM

Mark, that's truly a work of art. Very nice!

himespau 10-31-11 08:14 AM

That rack is sweet looking.

neurocop 10-31-11 02:14 PM

Quote:

Originally Posted by Mark Kelly (Post 13433311)
I've been working for a couple of years on a pet theory which is that what we call "ride quality" is chiefly an acoustic phenomenon. What we want is a frame which transmits road feel (the signal) without adding extra harshness (noise). The analogy is to a signal to noise problem in audio design and since this is a field in which I have some background, I started looking at ways of working with this.
...

This is a fascinating idea! We traditionally talk about "road feel" and "ride quality" using terms like frame stiffness, responsiveness, agility, etc. But as you say it can all be reduced to acoustics, in the sense that the bicycle is really just a sort of "transducer" that transforms and transfers energy between the rider and the road. What the rider feels is the way the bike sends this information to to rider. And this energy is, as you note, transmitted as mechanical vibrations (essentially sound waves). You idea sounds (forgive the pun) ingenious. Can't wait for the practical application.

RosyRambler 11-05-11 09:39 PM

Mark, that's a really nice piece of work for a self taught student!

What did you use to bend the tubes with?

And I hope you'll post more photos of any other racks you design and build.

Mark Kelly 11-06-11 01:28 AM

I used a cheap chinese tube bender because the local tool supply wanted over $200 for a Ridgid 400 series unit.

Cheaping out on the bender turned out to be an expensive decision in terms of scrap and rework required. Next time I'll buy a Rothenberger and be done with it.

RosyRambler 11-07-11 06:34 PM

Thanks Mark, I'll keep that in mind when it comes time to do my own building.

And I do hope you'll post up any other of your interesting creations...


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