Bending curved seat stays - how do you do it?

[joth jacobson]

I'm working on a frame with curved seat stays (Retrotec-ish). In looking at how others with similar curved seat stay designs have attached the stays at the seat tube, it appears that most have bent the stays at the top perpendicular to the radius bend for better tire clearance and easier joining. Can someone share examples/knowledge of how to bend a curved stay on a perpendicular axis?

[afwalker]

Here's the cat's pajamas:
Mr. Bender Bending Rodriguez - a set on Flickr
You can make some dies yourself out of wood, or use a tube bender like the Baleigh, the J2 squared, JD Squared, Inc. - Tube/Pipe Benders
and the Di Acro is a favorite also,
diacro bender | eBay
cheers
andy walker

[joth jacobson]

Here's an example from Black Sheep - curved seat stay that is brought into the seat tube at the top of the stay. How would one bend the curved stay at the top like that? I have a tubing bender, but the dies require a straight tube.

image.jpg

[afwalker]

Ok not so much of a bend then use a tubing roller like the HF
Tubing Roller
and get round dies from swagoffroad.com
Harbor Freight Tubing Roller Dies
Troy makes very nice dies since the ones that come with wont do the diameters you need.
cheers
andy

[bencooper]

I use a Hammill bender - it can cope with most curves I want to do on stays.

[joth jacobson]

Thanks gents. I feel like I'm not getting the question across correctly. I'm thinking of seat stays where from the side they have a curved look (ala Retrotect, Black Sheep, basically cruiser style), yet if you were to look at them from the top, they have an s-bend shape as well. Todd's sweet frames are a good example: black cat: Blue Velvet How does one get both the vertical curve and s-bends into a seat stay. I've got a tubing roller to get the gentle curve and a bender for creating s-bends, but am unsure how one would get both on one piece of steel? Thanks.

[adarn]

Boy, that's a good question.

I just finished a frame where I tried something like that. Here is a pic of the seat stays:


I curved them on a harbor freight roller first, and then managed to get a slight bend for more clearance on the wooden mandrel bender that I built.
I settled on just capping the stays and brazing them to the ST, but I've done some more experimenting and I think I can get them so that I can do them in the "fast back" style, or whatever they call that.

My mandrel bender, I believe works well for this because it has a lot of play. I sort of trashed it originally, thinking it wouldn't work for much, but the play in the arm allows me to follow the curve some and get a decent bend on the curved stays. So that's kind of neat. I just go super slow and check the on a surface plate to make sure they're all good.

[Meriwether]

I think this is one of those tricks that the ones that have figured it out don't share their secret.
I've done it once with an 8" radius MDF mandrel in a mill vise (very junky setup) keeping the big radius bend as close to vertical as I could possibly manage (magnetic angle finder). I didn't get it perfect but it worked pretty well. I'd use a smaller radius next time. Count the handle turns on the mill vise, you don't need a lot of bend for tire clearance. The frame I made was for Knards (29x3" tires) so i had to get a bit more bend but not that much. For smaller tire MTB's you may not need a second bend if you *rotate* the stays out from the centerline of the frame enough. Unless you want the S-bend look from behind of course. But if you look at Curtis' (Retrotec) Flickr you'll notice many frames don't appear to have a second bend for tire clearance and only the long swoopy bend you see from the side.

I think one way to do this would be to run the stay in a roller first but don't roll the entire tube. On the straight section of the tube you would then use an Anvil-type bender to get the 2nd bend. You'd somehow have to create a phase-keeper 'arm' - like the one on the Anvil but in the horizontal plane to keep it all squared up.

bender-sideview.jpgbender-SS-topview.jpg

[shand]

That's a neat setup. Are the G-clamps there just to hold the form together, or are they doing something else?

Steven

[Mike Mcdermid]

Thanks gents. I feel like I'm not getting the question across correctly. I'm thinking of seat stays where from the side they have a curved look (ala Retrotect, Black Sheep, basically cruiser style), yet if you were to look at them from the top, they have an s-bend shape as well. Todd's sweet frames are a good example: black cat: Blue Velvet How does one get both the vertical curve and s-bends into a seat stay. I've got a tubing roller to get the gentle curve and a bender for creating s-bends, but am unsure how one would get both on one piece of steel? Thanks.

You need one of these

[Meriwether]

That's a neat setup. Are the G-clamps there just to hold the form together, or are they doing something else?

Steven

Purely support since the screws and wood glue weren't doing their job.

[Rody]

Joth,

What you are asking to do is not an easily performed process.

Large radius seat stays are typically done one of two ways; a sweeping radius that contacts at the seat tube and then carries on to the head tube, ala Retrotec or a curved radius stay with a perpendicular bend for tire clearance, connection at the seat tube.

The first example is made by rolling a length of tube to extend from the dropout to the headtube. The tube is then marked at the ST intersection, a small pie shaped wedge cut out of the outside aspect and then bent to close and welded together. This allows the tube to be wider around the rear tire and then close in towards the center of the frame for the top tube area.

The second example is much harder to accomplish. In the example below, I made the perpendicular bend to clear the tire first using my hydraulic press on a long piece of tubing. That tube was then loaded into a roller with a modified die on the bent end (the die had much lower side wall height, terminating just shy of the tube centerline), which allowed me to roll the tube, drawing it through the die right up to the perpendicular bend. This gave a nice transition from the rolled aspect to the more acute bend to the seat tube.
retro29er.jpg
Hope this helps...

rody

[steve garro]

Pretty simple given the proper forms......
I would put in the tire clearance bend & then rake it on a mandrel.
- Garro.

[joth jacobson]

Thanks all. I had a sense that this was most frequently accomplished with custom/modified dies/forms. Wanted to make sure there wasn't something simple I was missing.

Rody - I like the idea of modifying the side wall on one of the roller dies. Seems a simple way to go.

That 3D tubing bender in the YouTube video will definitely haunt my frame building dreams - very cool!