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absolutely if I understand you correctly. You mean to cut the tube halfway-ish then bend it and reweld along the cut right? I do that on all my chainstays and anywhere I need to bend the streamline tubing I use. Works great because you save some of the original material and its easier than cutting the tubes at the right angles which is tricky so that they will line up perfect.
 

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Discussion Starter · #3 ·
That's close. I use 30/16 stays and when I bend them, especially the greater bends, they get quite a bit thinner in cross section if they don't buckle or fold.

I was thinking of cutting the tube completely to make the angel. I'm thinking that I will distress the tube a bit much to bend just part of it. Also, I keep a greater cross section if I have a full mitre.

Just looking for horror stories or problems to watch out for especially since these are chainstays.
 

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I've seen it done a few ways over the years. The way I liked the best was to basically cut a wedge out of the inside and bent around that. Weld up the seam and it looks really clean and the HAZ is a bit smaller. I've seen folks just cut the angle and do a full butt weld for the new. The prior I've only seen a couple times and have never heard of a problem. The latter I've seen be fine and I've seen broken. I think it's more about the skill of the builder than the limitations of the material.
 

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I've done it

Albeit only with with 3/4x1.5"x.049 box-section 4130. I was building a mountain bike frame for a fellow who is 400 pounds, and I couldn't conceive of any of the chainstays on the market being strong enough.

I cut at about 8 degrees, flipped, and butt welded back together. Then I installed a crossbrace on the finished stays that was welded in on both sides of the butt weld to help reinforce things.

So far (touch wood) it's been 3 years and I haven't heard of any problems.

For a more normal chainstay, I like the monkeyman's idea. Never done it, though.

-Walt
 

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I'll preface this by saying I've not tried it...but here's an idea, albeit a heavier option.

Sleeve the stay before the bend. Either tack it or pin it to the stay in an area that will cover apex of your bend. Complete the bend and then finish brazing sleeve in place.

I'd probably do all kind of crazy/fancy/unnecessary work on the sleeve trying to express an artisan's approach but certainly not necessary.

Again, I've not ever done this. ...Just an idea. YMMV.
 

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pvd said:
I'm thinking of doing some chainstays with chopped and welded bends. What do you folks think?
I think it's a great idea - though my builders (mass production factories) never wanted to do it.

Hence the "on-one wishbone" has mitred junctions, rather than cut and welded corners.

You could mitre and cap off one tube end... That could look neat. More weld area.

Ever tried anything with bits of plate in the chainstay area? - I've been working on that this afternoon after I heard Lynskey had a new water-jet cutter guy, and I wanted some more tyre clearance on our Ti frames...
 

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...Ever tried anything with bits of plate in the chainstay area? - I've been working on that this afternoon after I heard Lynskey had a new water-jet cutter guy, and I wanted some more tyre clearance on our Ti frames...
I have
 

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Titus used to do it on their Ti hardtail, the HCR.

Here´s how I did it. Not that god with the TIG so I braze. lathed end plugs with solid ends. braced them to the tubes, cut to the right angle and braced everything together. Looks good but have not tried it yet. Hope it works :)

 

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Discussion Starter · #11 ·
I did a test stay. I was concerned about the strength. I almost went over to a strut. I spent about 20 minutes staring at the stay. Then I gave it hell. I beat the **** out of it. Hammer, vise, bending...

It's funny. The welded seam was the strongest part of the structure.

I'm going for it. Pics later.
 

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Depending on how sharp the bend is, you may need a web gusset spanning the inside of the tube. This gusset would look a little like what Peter did, think of this gusset as something that would block the flow of water inside the tube, and get welded at the same time as the joint between the two pieces of tube and you get what I mean. The reason for the gusset is to prevent the new flexure mode you created from killing the tube in fatigue.

When i have done this in the past, I've done extreme angles with one tube intesecting another capped tube's sidewall. For less extreme angles, I take a wedge out of the tube about 3/4 of the way through a round tube (far enough so bending it closed doesn't produce ears), or all the way to the opposite wall on rectangular tubing. I then close the wedge and braze or weld the seam, grind it slightly (don't do this unless you do the next step too...), and braze on a patch over the seam that is either bent flat stock (rectangular tube), or cut from a curved (thicker wall, slightly larger diameter) round tube. In the case of the round tube, I've used pieces cut from the tops of the end cuts off unicrown fork blade tops, heat bent thicker tubes, etc. I wish I could find a picture....

edit: with welding, depending on the filler strength, no post weld grinding and no patch gusset might be ok. with brazing, the bronze isn't strong enough to prevent the joint from tearing out without a lot of build, so the gusset looks better and gives better clearance. That same issue is my only worry with Peter's joint pictured above. If that tube is a seatstay, it might be fine....
 

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rocwandrer said:
edit: with welding, depending on the filler strength, no post weld grinding and no patch gusset might be ok. with brazing, the bronze isn't strong enough to prevent the joint from tearing out without a lot of build, so the gusset looks better and gives better clearance. That same issue is my only worry with Peter's joint pictured above. If that tube is a seatstay, it might be fine....
that's the left chainstay, 3/4"-0.035.

The brazed area is 5 times greater than the cross section area of the 3/4tube. I'm a little concerned too. I'll let you know if it breaks...
 

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Peter E said:
that's the left chainstay, 3/4"-0.035.

The brazed area is 5 times greater than the cross section area of the 3/4tube. I'm a little concerned too. I'll let you know if it breaks...
the issue is if it subjected to bending stresses, and how those might be distributed by your plug, as it sounds like you already know... road or mtb use?
 

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pvd said:
Test peice. Same as the final version, but beat up, smashed and bent.
wonder how it would be in fatigue loading though? Driveside stays get screwed by fatigue in my experience - we stopped using chainstay bridges and switched to gussets on the outside as a common failure mode of our earlier frames was a fatigue propagating around the stay from the chainstay bridge weld.
 

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Discussion Starter · #19 ·
Fatigue is definately the real issue. I can only try and see how it works. I figure that if something survives the beat down test, it's worth a run or two down the hill.

My impression while pounding the stay was that the weld actually improved the structure of the tube. With bending the tube gets very thin cross sectionally. With this segmentation, it stays wider. The weld acts almost like a support beam around the tube as well. It didn't want to crush there. Putting an 0.035 cap between the tubes would be stronger, but i'm wondering now if that is needed. We will see. It would be a good time to have a cycleing test rig in a HALT chamber right now.

Strutting the bend with a capped segment would be the strongest, but adds a huge amount of work and changes the astetic.
 
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