Tube Bender?

[tnort...@gmail.com]

As I am ramping up for my next frame I am intrigued by the curved bridges seen between the SS. So I would like to attempt this but lacking  a tube bender I could  use some advice. I did make a bender for some racks making wooden  "pulleys". But now have a metal lathe. 

Also what wall thickness would  be appropriate ?

Thanks! 

Tom

NE Ohio 

[m-gineering]

depends on how good your tube bender turns out to be. I aim for roughly
the same thickness as the stays, but that probably necessitates a
mandrel bender.

--
Marten Gerritsen
Kiel Windeweer
Netherlands

[tnort...@gmail.com]

Do you think a aluminum mandrel would work? 

Tom

NE Ohio

My wife's touring bike came from Rotterdam! 

[m-gineering]

On 3/22/25 12:52, tnort...@gmail.com wrote:
>
> Do you think a aluminum mandrel would work?

Only issue I see is mounting the tubeclamp to the block, that takes a
bit more thought than cutting out a chunk and brazing in a piece of
steel (tip: tack two pieces of flat bat together and drill a tube sized
hole though the parting line)
I've used shoes from hard PVC and alumninium, they seem to hold up

> Tom
> NE Ohio
> My wife's touring bike came from Rotterdam!

bike4travel?

[tnort...@gmail.com]

Yep! Bikes4travel. We actually stay at Marco's home for a few nights in 2023.

Tom

NE Ohio 

[Jon Norstog]

You can heat-bend 4130 tubing.   It helps to have a mandrel - for instance pisces of an old auto front CV joint.  Plain 4130, .9 mm/.035" diameter is a good choice.  It may take you several tries to get the hang of it, but you will learn a VERY useful skill.

jn

"Thursday"

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[Alex Meade]

Tom,

Here are a couple of IG videos I did, showing a fancy way and a crude way that both work just fine for what you're trying to do. Both are 4130 tubing, but the second technique might not work for 1/2" diameter stock.  You certainly don't need as fancy as the first tool, but it should give you ideas of what you can make on a lathe:

https://www.instagram.com/p/Cim_YN6vtWV/

https://www.instagram.com/p/C-KwVffOC70/

Hope this is helpful,

Alex

Alex Meade Tools

[david levy]

https://www.vevor.com/pipe-tube-bender-c_10843/vevor-pipe-bender-manual-bench-bending-machine-3-8-1-tube-bender-set-7-dies-p_010584466314?adp=gmc&utm_source=google&utm_medium=cpc&utm_id=17805318448&ad_group=137797733223&ad_id=611438968932&utm_term=&gad_source=1&gbraid=0AAAAACq8bLUFlWVX7WM_d_947mCZfdsuI&gclid=Cj0KCQjwv_m-BhC4ARIsAIqNeBuGvlPD4jB5ue6yT6j6CFMGD1hW4aRWuKT9-s19c9nLDn157Fbuwd8aAp6IEALw_wcB

Dave Levy
Ti Cycles Fabrication (Bicycle stuff) 
Cedar Ridge Fabrication (Car stuff) 

15707 NW McNamee Road Portland OR 97231 USA
+1 503-621-9670 

Ti Cycles Facebook  |  Cedar Ridge Facebook

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[Gef]

Alex,

How much filler rod do you put in there and how hard is it to get out? 

Gef

[Chuck Griffon]

Just as an aside, McMaster-Carr has low melt alloys at you could use to reinforce the tubing for cold bending.

E.G.- 

https://www.mcmaster.com/product/8921K22

Cheers

Jim Holly

Chch, NZ

[Alex Meade]

Chuck,

Bending alloys, aka "Woods Metal", "Cerrobend", "Cerrosafe", "Lipowitz' Alloy" are amazing. I use it for tight bends on stuff that would otherwise buckle, including bending KVA stainless fork blades to a 4.5" radius. It's a lot more work than a decent bender, but for just one part of a specific diameter and bend radius, it's much quicker than making a bender. It's almost magic stuff for bending.  For those that don't know, it melts at 158F, so just hot water will do it.

Alex

http://www.alexmeadetools.com

[Mark Bulgier]

Jim Holly wrote:

>  McMaster-Carr has low melt alloys at you could use to reinforce the tubing for cold bending.

Interesting.  Jim, have you used that McMaster metal?  I notice bending thinwall tube is not mentioned as one of its uses, but maybe it's excellent for that anyway?

I have used Belmont Bend 158 and Cerrobend, which are nearly identical to each other but slightly different formulas to the McM stuff.  But that was decades ago, no recent experience.  They're both formulated specifically for bending, and they worked perfectly, letting me make ripple-free tight-radius bends in thinwall.  I see now Belmont shows the price as $140 for 2 lb, or about 4 times as expensive as the McMaster stuff.  So the McM alloy might be a great deal if it works as well.

Note, this stuff is very toxic, and a bit of a PITA to use, so I sure wouldn't use it on brake bridges, which have no need for being especially thinwall. I bend 'em with a Ridgid 398, usually available used for ~$50, ebay example here.  Example bend:

That's probably .035" (.9 mm) CrMo, though I don't remember for sure. For a bridge, it hardly matters what you use.

Pro tip: Almost any bending of metal leaves residual stress that makes it easier to bend it back in the opposite direction, just a little.  Once you bend it back more than "a little", that effect goes away, and the metal is now harder to bend, due to work-hardening.  So for best strength and stability, any time you bend something, over-bend it just slightly, then bend it back a little.  To know how much is best, you'll have to experiment, but any little bit you do is probably beneficial, whether it's 'optimized' or not.  You can feel and measure it — the first little bit of bending back is easier.  I don't remember if I did that on the bridge in the pic, but I would recommend it.  So you'll get a bend radius that's just slightly larger than how it comes right off the bender.

Tip #2, check out Nestor's excellent way of mitering bridges on a belt-sander with a "small wheel attachment"

https://flic.kr/p/2khHNt4

Maybe not reason enough to buy or build a fancy belt-grinder, but there are plenty other reasons.  I wouldn't want to be without mine, but I'm spoiled...

Honestly though, a hand-file is so fast, nothing else needed.  In at least one way, mitering curved bridges is easier than straight ones, because you can just clamp them between two flat "things" (soft jaws in your bench vise might be enough), and that automatically clocks the miters to be in the same plane.  Eyeball accuracy is close enough for the angle, brass will fill any little gaps.

Mark B in Seattle

[tnort...@gmail.com]

Thanks Mark. 

In between working on my frame I made some mandrel out of 1.5" cherry.  Did the turning on my wood lathe. 

Tom

NE Ohio 

[Andy Walker]

Surprised the Ridgid tubing bender hasn't been mentioned. I have a 3/8" and the 1/2" and works great. 3/8" for racks, 1/2" for bridges.

Or there is a Vevor multi-size bender could work.

To minimize distorting the tube, it's easy to put sand in and tape the ends, works ok. Watch the silica dust.

johnnealeltd.co.uk used to sell a non-toxic wax but I can't find the name of it and the label faded so badly on my bag I have no clue:)

andy walker

cape girardeau, missouri

https://www.mcmaster.com/33745A62/

https://www.amazon.com/VEVOR-Pipe-Bender-Manual-Tubing/dp/B0BNBBLR5X/ref=asc_df_B0BNBBLR5X?hvadid=79989603081951&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4583589122445313

[Dan Chambers]

" johnnealeltd.co.uk used to sell a non-toxic wax "

That's WS8 resin. I use it occasionally.
It melts at 70°C, is water soluble and non-toxic. Melt the granules like wax on a stove, fill the tube, bend, warm the tube to melt it out (and keep since it's re-usable), then flush any residue with hot water. Info sheet: https://johnnealeltd.co.uk/Resin%20WS8%20TDS.pdf

Still available: 5 Litres/Kgs £66 UK supply or £100 worldwide shipped. https://www.johnnealeltd.co.uk/shopresinws8.html

John Neale do also make a traditional Cerrobend-type metal filler, but the bismuth-tin-lead-cadmium composition puts me off.

All the best,

Dan Chambers

[Mark Stonich]

One  of the cleverest gents I know put a smooth, relatively tight radius bend in 0.028" x 7/8" 4130. He brazed a cap on one end and a 5/8"  fine thread nut on the other. Then he put in all the sugar sand that would fit, even used something to vibrate the tube, to get the sand as compacted as possible. Then he screwed a bolt through the nut to pressurize the sand.