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How to arch a ST?

1576 Views 23 Replies 9 Participants Last post by smdubovsky, Jun 25, 2009

smdubovsky

Discussion Starter · Jun 17, 2009

I've got the first frame done and have been riding it (I'll get off my lazy butt and post pics eventually.) Im already thinking about the next one... Was thinking of arching the seat tube. Purely for asthetics to partially mimic the arc of the tire. Something like ~20" radius. What the best way to do this? I was thinking a ring roller might work better than a mandrel type given the gentle curvature. Should I be using a straight gauge or can I get away w/ a (single) butted tube if I don't get too close to the butt? (A ring roller might limit that anyway) Any idea on diam/wall thickness that would work best?

Thanks for any suggestions/tricks that'll limit the number of practice/scrap pieces

SMD

1 - 20 of 24 Posts

Walt

· #2 · Jun 17, 2009

Straightgauge.

Butted tube isn't strong enough to have this done to it, IMO. Use straightgauge .035.

I've seen a bunch of ways to do big radius bends - if you search back on the coconino blog, I think you'll find some useful pictures.

-Walt

smdubovsky said:
I've got the first frame done and have been riding it (I'll get off my lazy butt and post pics eventually.) Im already thinking about the next one... Was thinking of arching the seat tube. Purely for asthetics to partially mimic the arc of the tire. Something like ~20" radius. What the best way to do this? I was thinking a ring roller might work better than a mandrel type given the gentle curvature. Should I be using a straight gauge or can I get away w/ a (single) butted tube if I don't get too close to the butt? (A ring roller might limit that anyway) Any idea on diam/wall thickness that would work best?

Thanks for any suggestions/tricks that'll limit the number of practice/scrap pieces

SMD

smdubovsky

Discussion Starter · #3 · Jun 17, 2009

Thank Walt. Love the look of his curved top tubes. Searched his whole blog and it seems Steve uses a form to press TTs into (dig the come-a-long idea.)

Anyone ever used a ring roller? I would be my first 'tool of choice' since I can borrow one

If one can cold press 0.035 into a form I would think a roller could do the job too.

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shiggy

· #4 · Jun 17, 2009

smdubovsky said:
Thank Walt. Love the look of his curved top tubes. Searched his whole blog and it seems Steve uses a form to press TTs into (dig the come-a-long idea.)

Anyone ever used a ring roller? I would be my first 'tool of choice' since I can borrow one If one can cold press 0.035 into a form I would think a roller could do the job too.

Ring roller = radius bender = tubing roller?

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smdubovsky

Discussion Starter · #5 · Jun 18, 2009

shiggy said:
Ring roller = radius bender = tubing roller?

Yup, thats what Im talking about. I've seen tiny ones that are used to make actual jewlery rings so Im guessing that why I've always heard it called that? I've got a JD2 bender for roll-cage tubing but can't make a die large enough to do the ST. I'll either have to fabricate something like steve's setup or borrow a buddies roller (and borrowing is far easier if it turns out to work

)

Thylacine

· #6 · Jun 18, 2009

I *heart* Mandrel Bending.

verticult

· #7 · Jun 18, 2009

that ring roller is slick.

shiggy

· #8 · Jun 18, 2009

smdubovsky said:
Yup, thats what Im talking about. I've seen tiny ones that are used to make actual jewlery rings so Im guessing that why I've always heard it called that? I've got a JD2 bender for roll-cage tubing but can't make a die large enough to do the ST. I'll either have to fabricate something like steve's setup or borrow a buddies roller (and borrowing is far easier if it turns out to work )

Go for it.

Cracked Headtube

· #9 · Jun 18, 2009

I saw some nice images on RetroTech's flickr page using this tool, for TT bends.

unterhausen

· #10 · Jun 18, 2009

Thylacine said:
I *heart* Mandrel Bending.

must be nice. Don't think I could afford that

Schmitty

· #11 · Jun 18, 2009

Also called a band roller.. way better for large rad bends than a mandrel bender.

-Schmitty-

unterhausen

· #12 · Jun 18, 2009

Schmitty said:
Also called a band roller.. way better for large rad bends than a mandrel bender.

-Schmitty-

Are you talking about the three roller bender as shown above? I'm having a hard time imagining it being better than a mandrel bender for any bend on thin tubing

smdubovsky

Discussion Starter · #13 · Jun 18, 2009

unterhausen said:
Are you talking about the three roller bender as shown above? I'm having a hard time imagining it being better than a mandrel bender for any bend on thin tubing

Yes, hes talking about the roller bender above. Imagine having to buy a die (& shoe) for a 20" rad bend? A 5-6" die from JD2 is ~$250 (its ALOT of steel.) Granted, thats for heavier walled tubing but alot of of commercial benters work w/ the wheels. The huge advantage is you don't need a new die for every radius. Its adjustable.

What you may not know is that the tube typically isn't bent to the final operation in one shot. You apply a little pressure w/ the center roll, work the tube back and forth, apply a little more pressure, work back and forth, and on-and-on. It very gently brings the tube to shape. The thinner the tube the more 'steps' you have to use. If the wheels are a close fit to the tubing diam it greatly helps reduce the chance of distortion too.

If you really want to get into thin wall bending, I think you have to get into the drawn over mandrel (ball) type benders. Those are really big bucks, but nothing on a bike requires that type of stuff (I think its how all thin stainless exhaust tubing is done)

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unterhausen

· #14 · Jun 18, 2009

I thought he was talking about an internal mandrel bender.

coconinocycles

· #15 · Jun 19, 2009

smdubovsky said:
I've got the first frame done and have been riding it (I'll get off my lazy butt and post pics eventually.) Im already thinking about the next one... Was thinking of arching the seat tube. Purely for asthetics to partially mimic the arc of the tire. Something like ~20" radius. What the best way to do this? I was thinking a ring roller might work better than a mandrel type given the gentle curvature. Should I be using a straight gauge or can I get away w/ a (single) butted tube if I don't get too close to the butt? (A ring roller might limit that anyway) Any idea on diam/wall thickness that would work best?

Thanks for any suggestions/tricks that'll limit the number of practice/scrap pieces

SMD

yo, dude - Steve here. yah - go 20" or even 24" radius on a wooden form.........less is more........go 1.125 x .035 & get a 26.8 seatpost. pack the tube with sand & start with a long piece - you'll need it for leverage. get a buddy to help, too. way easier. Steve.

Thylacine

· #16 · Jun 20, 2009

unterhausen said:
must be nice. Don't think I could afford that

Take 60 bucks out of your pocket, go to local mandrel bending place, would cost about 5-10 bucks per bend. Any bend you like. Zero distortion.

Probably not a massive help if you only wanted one, but you could easily do a bunch and probably even sell them here.

smdubovsky

Discussion Starter · #17 · Jun 20, 2009

Thylacine said:
go to local mandrel bending place...

How does one find someone to do that? I do a lot of machining/metalwork in my other hobbies and have never run across a shop that'll do that. Disclaimer: I live near DC - so unless you're looking for a doctor, lawyer, or politician to shove something up your a$$, you're out of luck.

unterhausen

· #18 · Jun 20, 2009

performance car exhaust shops will have a mandrel bender. I would assume there are some near you.

shiggy

· #19 · Jun 20, 2009

smdubovsky said:
Yes, hes talking about the roller bender above. Imagine having to buy a die (& shoe) for a 20" rad bend? A 5-6" die from JD2 is ~$250 (its ALOT of steel.) Granted, thats for heavier walled tubing but alot of of commercial benters work w/ the wheels. The huge advantage is you don't need a new die for every radius. Its adjustable.

What you may not know is that the tube typically isn't bent to the final operation in one shot. You apply a little pressure w/ the center roll, work the tube back and forth, apply a little more pressure, work back and forth, and on-and-on. It very gently brings the tube to shape. The thinner the tube the more 'steps' you have to use. If the wheels are a close fit to the tubing diam it greatly helps reduce the chance of distortion too.

If you really want to get into thin wall bending, I think you have to get into the drawn over mandrel (ball) type benders. Those are really big bucks, but nothing on a bike requires that type of stuff (I think its how all thin stainless exhaust tubing is done)

Here is a TT being formed

https://www.velocipedesalon.com/forum/showpost.php?p=101500&postcount=15

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Schmitty

· #20 · Jun 20, 2009

shiggy said:
Here is a TT being formed

https://www.velocipedesalon.com/forum/showpost.php?p=101500&postcount=15

Yup that's it... the Cadillac version of the manual machine posted previously.. serious $.. used mainly for hand rails, boat deck rails, etc. Mandrels are good for bending in a specific area of a tube.. ring/band rollers rock at bending the whole tube.. very adjustable as well..the machine above could prodcuce many many different bends as pictured... no screwing around with mandrels.

-Schmitty-

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