Curved Seat Stay Bridge Question

[jclay]

Those of you who make SS bridges like this one:

https://www.flickr.com/photos/49353569@N00/14817266472/

What tubing OD and wall do you use?

Thanks

[e-RICHIE]

3/8 inch or 1/2 inch and 22 gauge atmo.

[fortyfour]

I typically use .5" O.D. Seamless 4130 Aircraft tubing with .035" wall thickness. I mostly buy this in 8' lengths from Aircraft Spruce and occasionally Wicks.

[David Tollefson]

1/2" OD and either .035 or .028 thickness. Though I use them for CS bridges as I go with a wishbone seatstay configuration.

[jgrano]

For those of you who make the little bridges and wishbones. Is there a favorite bender or are they all pretty basic for that size tubing? Also I assume it's best to either pack sand in the tubes or fill & freeze?

Maybe something like this one - 370-FH Triple Head 180° Tube Bender | Imperial Tools

[Will Neide]

For those of you who make the little bridges and wishbones. Is there a favorite bender or are they all pretty basic for that size tubing? Also I assume it's best to either pack sand in the tubes or fill & freeze?

Maybe something like this one - 370-FH Triple Head 180° Tube Bender | Imperial Tools

When doing bridges, I usually keep it simple and use a 26" rim. Clamp one end and just roll it.

[David Tollefson]

This in 1/2".

41gbAEaR1cL._SY450_.jpg

[Alistair]

Maybe something like this one - 370-FH Triple Head 180° Tube Bender | Imperial Tools

I bought one of those benders for rack making purposes years ago and it was not up to bending cro-moly. Probably fine with copper or aluminum tubing but using steel I sheared off the hook that anchors the end of the tubing in pretty short order.

Just fyi.

Alistair.

[David Tollefson]

Haven't had a problem with mine. Add grease to the slider and 180 degree bends go just fine (though mostly I only go as far as 60 degrees, which is plenty). No need to fill the tube with sand or anything.

[Alistair]

Haven't had a problem with mine. Add grease to the slider and 180 degree bends go just fine (though mostly I only go as far as 60 degrees, which is plenty). No need to fill the tube with sand or anything.

I should have added, and meant to add, "ymmv" at the end of my post of course. Glad to hear that yours is going strong. Mine worked fine, until it didn't. Who knows, maybe a flaw in the casting.

No big deal though. I moved onto the Swagelok brand of lever benders that have the rollers in the forming shoe instead of a friction pad. Those things are nice. So smooth and precise. Unfortunately, they are also rather expensive.

I also have a couple of the Ridgid lever benders, like the one you linked to above. Those have served me well, even if they are not as nice to use as the Swagelok's (imo/ime).

Alistair.

[Zimmermanbicycle]

This mosly

I typically use .5" O.D. Seamless 4130 Aircraft tubing with .035" wall thickness. I mostly buy this in 8' lengths from Aircraft Spruce and occasionally Wicks.

[jgrano]

Thanks for the response. I'll have to pick one up shortly.

I've used one at a previous job for bending stainless tubing and it always came out horrible past 60 degrees. Good to know it was probably just an issue with the bender.

[Eric Estlund]

This is one of those questions that doesn't really have a "right" answer. You get to pick the tube that gets the job done and looks the way you want. Diameter and curve radius are all over the map based on what the builder is shooting for with both functional and visual effect.

[jclay]

Thanks for the information all. I have a stick of 3/8 x 0.028"; see how that turns out.

[duanedr]

I've started messing around in preparation for a front rack and have found that 90* with 3/8 x 0.028" kinks with a 15/16th radius bender like the one pictured above. I haven't tried with sand or grease on the slider or other tricks so, I'll keep messing around.

Love the idea of clamping it to a rim and using that as a mandrel!

[Chauncey Matthews]

I've started messing around in preparation for a front rack and have found that 90* with 3/8 x 0.028" kinks with a 15/16th radius bender like the one pictured above. I haven't tried with sand or grease on the slider or other tricks so, I'll keep messing around.

Love the idea of clamping it to a rim and using that as a mandrel!

Do you have the Ridgid bender? I bent a full 180* with mine yesterday. The key is to keep the shoe pressed firmly against the tube (grease helps here) and make sure the tube stays fixed. It only kinks if it moves.

[duanedr]

I have an older Ridgid. I'll try greasing the shoe tomorrow. Otherwise, i'll have to make another fixture...which is fun but, i'd like to make the rack instead.

Thanks! I'll update with results in a day or two.

[fortyfour]

I have an older Ridgid. I'll try greasing the shoe tomorrow. Otherwise, i'll have to make another fixture...which is fun but, i'd like to make the rack instead.

Thanks! I'll update with results in a day or two.

If that does not work, try .035" wall thickness. .028" wall thickness can be tricky as it tends to buckle easily even at small O.D.'s

With any bend of any type, this golden rule applies:

· Maintain point of tangency throughout the bend.

IF the follower gets ahead of or behind that point, so that the tube is not fully supported at the point of tangency, it will begin to buckle, wrinkle, bend etc. As the tube diameter goes up and wall thickness decreases, fully supporting the tube profile both inside and out becomes even more critical. The material of the tube on the inside of the bend is compacted while the outside of the tube/bend is being stretched. This is what they call a "wiper die" or "internal mandrel".

I know those who do use sand as an "internal mandrel", often have the most success using play sand which is very fine (I think the home depot sells this for sandboxes for kids). The finer the grain, the better luck you will have. Make sure you tamp/tap it down so it settles and there are no pockets or air inside.

[duanedr]

Greasing the shoe worked fantastically!

Now I just have to find the right way to measure out the bends so I get the right finished dimensions etc. I'll do some searches here and i'm pretty sure i'll find prior posts that will help.

[afwalker]

Thread migration! size/thickness on SS bridge bending, now sort of rack making, still about bending 3/8 0.028 SS tubing.
That's what I make my rack out of, and many bridges too, but in 4130. This table helps me line up and measure the rack bends.
Just a Ridgid 3/8 (ohh that swagelok is pretty, must resist and just grease the anvil)
mounted under a bending table with enough spacers to get it lined up. It's a big help on racks. No dimpling yet.
Idea from Carl Snarl during a metal guru class I attended.
9288643086_19a8b8952d_z.jpg
https://flic.kr/p/f9NHYJ
cheers
andy