Curved seat tubes

[Boedie]

Hi all,
For some reason, the search for the perfect curved seat tube seems to be like the elusive holy grail to me right now. I was curious what folks think of curved seat tubes, particullary for 29ers? I know that those who offer curved seat tubes on their bikes like to keep their processes under wrap as to not disclose their secrets. What are the tools of choice? Benders, rollers, home made forms?
Thanks.

[Chauncey Matthews]

Yo Chris!
I once did a fixed gear frame with a curved st made from 1.125x.035- packed w/sand and bent over a wood mandrel. It worked, the bike had 355mm stays....and looked pretty goofy with the seatpost laying back at a funky angle (dug up a pic curved+st+fixed+001.jpg (image)) it shoulda had a level tt...still a fun ride though.
Rick Hunter does the best curved st's, imho swamper | Flickr - Photo Sharing!
I think a scalloped seat tube or one offset onto the dt are cool options too.
Did you know that TT reissued their curved st as well?

[Clockwork]

I've bent 1.125 x .035" 4130 over a wood mandrel as well with good results--no sand even.

Track Clockwork

-Joel

[Boedie]

Chauncey, Joel
Thanks for the replies. Chauncey, I hope your body has mended and you are back at it. Your curved seat tube example looks pretty good. I had heard that True Temper had reissued the curved seat tube. I'l give the wooden mandrel a try. I have a mandrel that I can hog out for 1.125 tubing. Part of my concern is to have enough straght seat tube up top for the seat post to have adjustability. That looks feasible with both of your examples.
Thanks,

[Chauncey Matthews]

My problem is that it's hard to match the wheel radius using the wood mandrels- the tight question mark bend bend to the straight top is what makes the TT tube a winner for me.
Then again...http://storage.canalblog.com/61/92/116602/59301871.jpg

[Boedie]

Chauncey, I could not open that link for some reason. I've got a good example of a 29er curved seat tube in the shop that I'm trying to recreate. It's has one radius, which matches the rear wheel pretty good and gives lots of mud clearance. The radius that I have on hand is about 8 inches I think. I'll spend a little more time on it today. Thanks.

[steve garro]

Chauncey, I could not open that link for some reason. I've got a good example of a 29er curved seat tube in the shop that I'm trying to recreate. It's has one radius, which matches the rear wheel pretty good and gives lots of mud clearance. The radius that I have on hand is about 8 inches I think. I'll spend a little more time on it today. Thanks.

I would think you would need more like ~ 20" radius - Garro.

[Chauncey Matthews]

Hmmm, the link works ok here but don't ask me to explain why ! ;)
Here's the main site, you've probably seen it already, but I just love this guy's style- Kris is the master of the offset seat tube. Julie Racing Design - kustom bikes

[Boedie]

Pretty cool stuff. I had heard of JRD before but never really checked out his stuff. That's one way to get more clearance and short stays, but man, talk about more finish work in the bb region. ugggh.

Just finished off my supply of 28.6 straight gauge. Still not happy with the results. I still get a slight ripple in the tube, which if I look closely at the example I have, it has a slight bulge that shows up through the powdercoat. So maybe I'm being too picky. Oh well, I'll have to order some more and try a few more ideas. I checked out the true temper seat tube on a few builder's complete bikes. I think it looks a little goofy, personally. A better track bike application. I'm not crazy how it tapers up to the top. Thanks for the link, Chauncey.

[steve garro]

FWIW, I think that of all the builders Don Mc Clung's curved ST's work for me. I have other ways of achiving the balance of front & rear on my bikes & I have my own style not {currently} using curved ST's.......That being said, my pro-tools 3-ring would do what you are trying to achive in minutes.. - Garro.

[Boedie]

Steve, when you roll a tube, do you end up with a slight kink on each end?

[steve garro]

Steve, when you roll a tube, do you end up with a slight kink on each end?

Yes, it's called "tail" in bending terms, although you can get a varied radius if you have two people and adjust the pressure on the rollers.. - Garro.

[Boedie]

So if I understand this, you are suggesting that if you have one person tighten the top roller slowly while the other person rolls, then you can avoid that kink? I'll have to give that a try. Thanks Steve.

[steve garro]

So if I understand this, you are suggesting that if you have one person tighten the top roller slowly while the other person rolls, then you can avoid that kink? I'll have to give that a try. Thanks Steve.

Or the other way around - let off on the pressure on the opposing end of the tail. - Garro.

[bellman]

Bodie, I think what you are talking about is what happens naturally at the end of the tube, it is the part that never passes under the center roller. The tighter the radius, the longer the section. To avoid it you roll a longer piece than you need and cut the section out that you want.

[Archibald]

I can bend 1.25 4130 with .035 wall into a 24" diameter circle with no kinks. It's is so awesome being me.

[steve garro]

I can bend 1.25 4130 with .035 wall into a 24" diameter circle with no kinks. It's is so awesome being me.

Me too. - not so awesome as being you, tho...... - Garro.

[steve garro]

Bodie, I think what you are talking about is what happens naturally at the end of the tube, it is the part that never passes under the center roller. The tighter the radius, the longer the section. To avoid it you roll a longer piece than you need and cut the section out that you want.

Yes. this is the "tail" - but, what I am talking about is achiving more of a Golden Mean/Rectangle/ http://www.vashti.net/mceinc/unfold4.htm / Nautilus shell curve by starting fresh at the tail each time & easing off as you go along the radius - Capish/Sabe? Off to work! - Garro.

[bellman]

I got you steve, but I think boedie was looking to avoid the kink. I could be and probally am wrong though:)

[steve garro]

I got you steve, but I think boedie was looking to avoid the kink. I could be and probally am wrong though:)

can't be done - COGS yo. Start with an 8'er. - really outta here now - Garro.