# Tube bending: Cold Setting vs Heating



## j.m. (Mar 13, 2011)

I am going to curve my seat stays so the top tube makes a smooth curvedown to the dropouts. I was wondering whether I should just fill the tube with sand, cap the ends, and bend it around a wooden form or if I should add some heat with a propane torch. If heating is good, how much heat?

Jon


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## MPU (May 15, 2009)

Cold bending works fine. I just made such seat stays for my frame. Just fill them with sand and bend away.
Marko


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## j.m. (Mar 13, 2011)

But will there be any bad effects if I use heat? I know heat will make it easier to bend and I will get less spring back, but at what point do I damage the tube?

Jon


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## MPU (May 15, 2009)

It's not difficult to bend cold and I see no benefits with heating. 
Marko


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## SSearchVT (Sep 6, 2007)

Is it steel or aluminum? Aluminum work hardens when bent cold significantly more than steel. Steel loses it's temper when heated more than aluminum... Is the overall amount of bend (bend radius to material size) significant enough to be a concern?


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## edoz (Jan 16, 2004)

Anything on a bike frame can be done cold, and it's best not to heat it if you don't have to. It sounds like what you're wanting is a nice graceful arc, which will be even easier cold. Depending on the wall thickness, you could even get your bend without filling the tubes. I can get .035" to do a 15 degree bend on a 6" radius cold and unfilled pretty easily. It all depends on how well the tube is supported during the bending.
If you don't know how much heat to use, you're probably going to over heat them. My advice (since it sounds like you're emotionally attached to the idea of heating them) is to bend the tubes for your frame cold, and then play around with a bunch of extra tubing doing heated bends. Get on Google and find your self a color chart for heating steel. You'll be able to get an idea of how hot it is by the color, and then gradually heat the tubes and see how hard they are to bend and how smooth the bends are. Do test bends at different temps, and while you're searching, research how the metal is affected by different temperatures. You'll learn how hot is too hot, and what it looks like. Have fun.


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## j.m. (Mar 13, 2011)

That's exactly what I was looking for, thank you. I was looking for a suggestion of heat by color with the different blues, browns and greys. I will be making a fully supported curve out of mdf to bend the tube against. It looks like the radius of the bend will be about 2.5-3' so, yes, very gradual. The stays are the standard tapered ones that come in the Nova '29er' tubeset.

How much smaller than the actual radius should I make the form?

Jon


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## edoz (Jan 16, 2004)

j.m. said:


> How much smaller than the actual radius should I make the form?
> 
> Jon


Well, that's where it gets a bit fuzzy. I've never used the Nova tubing, so I really don't know how springy it is. I'd guess it's got a bit more than straight gauge 4130, but I couldn't say for sure without trying a couple of pieces. From what you've described, I'd make a 2.5' form and you'll end up with a little larger. How much larger will tell you how big your next form should be.


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## j.m. (Mar 13, 2011)

Or how much I should take off the current form.

Would a flat piece of 3/4" mdf be okay with a square cut edge? Or would I need to radius the edge to fit the tubing?

Jon


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## j.m. (Mar 13, 2011)

I made my form and bent the stays today. It was surprisingly easy. No sand, no heat, and no kinks or flat spots!

Jon


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## RCP FAB (Jun 15, 2011)

pictures?


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## j.m. (Mar 13, 2011)

I've been really busy at work, I'm switching shops. I'll get some pics tonight.


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## jgerhardt (Aug 31, 2009)

I thought it was generally a bad idea to bend butted tubing?


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## Walt (Jan 23, 2004)

*Seatstays are ok*

It is not always a bad idea to bend very thin wall tubing - but things get worse and worse as the diameter increases - ie, it's not hard to bend .6mm wall, 12.5mm diameter tubing, but impossible to do .6mm x 31.8mm, or whatever. So the tubing being butted isn't the problem in itself, but most folks won't bend main triangle butted tubes because they're too large/thin and just buckle or end up with problems down the road. You could certainly bend, say, 1.2/.9/1.2x28.6 or something like that. But most butted tubes used for front triangles are .6mm or thinner at the centers, and that just doesn't work out well.

Seatstays usually aren't butted anyway, and they're so small that they're easy to bend cleanly and safely.

-Walt



jgerhardt said:


> I thought it was generally a bad idea to bend butted tubing?


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## unterhausen (Sep 28, 2008)

the butting on stays only makes it so they aren't really thick at the small end. I imagine some brands had more trouble getting that right than others.


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## ramble (Aug 26, 2011)

I've never bent anything that big, but all the experience I've had with bending is that cold is fine, and you just need to support the outside really well. Thicker walls and un-heat-treated is easier (less brittle/inclined to buckle instead of bending), and look out for seams. I can't remember if Nova stuff is seamless or not, but I found out the hard way that at least some of Deda's SS's are seamed and the seam will split in many cases. I've had the best luck putting the seam on the inside of the bend. I wouldn't heat it up.


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## j.m. (Mar 13, 2011)

Almost done!


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## mbeardsl (Sep 9, 2009)

Looks familiar, you in the Raleigh area?

Is that a split seat stay for belt drive?


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## j.m. (Mar 13, 2011)

mbeardsl said:


> Looks familiar, you in the Raleigh area?


Maybe.............



mbeardsl said:


> Is that a split seat stay for belt drive?


Yep!


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## mbeardsl (Sep 9, 2009)

Nice lines!
Can't wait to see it finished and maybe on the trails sometime.


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## jgerhardt (Aug 31, 2009)

I have always wondered how much extra force those seat stays are putting on the top tube being attached there instead of at the seat tube. I would assume that you would ensure that they are attached well within the thicker section of the butt, however I could only assume that would require a much larger butt than normal and would also take away from the butt located at the head tube.

That said, I really do like the look of those bent seat stays.


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## febikes (Jan 28, 2011)

jgerhardt said:


> I have always wondered how much extra force those seat stays are putting on the top tube being attached there instead of at the seat tube. I would assume that you would ensure that they are attached well within the thicker section of the butt, however I could only assume that would require a much larger butt than normal and would also take away from the butt located at the head tube.
> 
> That said, I really do like the look of those bent seat stays.


J.M. and I worked on the bike together, he did all the design, miters, tube bending and such. I tried to talk him into doing straight stays but he got bent and in the end it turned out really nice.

His miter work was very good...


It is hard to tell from the photos but the stays are actually welded at the seat tube an also along the top tube. I think it is strong way to do the stays but really time will tell. The tubing is NOVA 858 with fairly long butts.


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## j.m. (Mar 13, 2011)

If you think about the distribution of forces, this way is actually a little easier on the bike.

This method has also been used on a few dirt jump frames in the past with excellent results:









If it'll stand up to that kind of abuse it's obviously strong enough for a trail bike.


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