How to bend Sissy Bars?

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wheelbender6

wheelbender6

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Saw this bike on Pinterest (it aint mine) and admired the bends in the sissy bar.
Is there a simple way to make those bends without ruining the chrome, like conduit benders or propane torches?
bent sissy.jpg
 
I would think conduit or fuel line bender. Maybe with some masking to protect the surface? Give it a go and report back
 
Try going to @tjwilson 's build thread for that bike and see if he shows how he did that.

https://ratrodbikes.com/forum/threads/shortbow.109804/
I would encourage you to look through the build thread frm the start to be amazed by his work, but if you just want to see how he MADE the sissy bar, you can start on page 5. There is nothing stock about that build. Also, it's not chromed, it's polished.
 
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axeman88 said:
As a mechanical engineer, I look at those bent tubes and see reduction of load capacity, not necessarily beauty. That frame has a fair amount of extra mass going along for the ride. Form foils function!
Click to expand...
tenor (8).gif
 
axeman88 said:
As a mechanical engineer, I look at those bent tubes and see reduction of load capacity, not necessarily beauty. That frame has a fair amount of extra mass going along for the ride. Form foils function!
Click to expand...


It's a modern muscle bike. If there was ever a genre of bicycles that screamed artistic sexy curves over efficient structural design it would be the muscle bikes of the 60s and 70s. Artistic flare trumped function every single time. :D
 
axeman88 said:
As a mechanical engineer, I look at those bent tubes and see reduction of load capacity, not necessarily beauty. That frame has a fair amount of extra mass going along for the ride. Form foils function!
Click to expand...
I was afraid of that, axeman88. I weigh well over 2 bills, so the reduction in strength will be an issue.
 
wheelbender6 said:
I was afraid of that, axeman88. I weigh well over 2 bills, so the reduction in strength will be an issue.
Click to expand...

Hey that's my bike!
Pretty cool to see someone wanting to do a sissy bar somewhat similar.

Yeah function.... pfffft ;).
Actually putting that curve in there had me sweating a bit. I monitored the dimensions for a good six months, totally expected to have to redo them but they've held up to date. A few caveats though. The sissy is scratch built using tubing with a thicker wall (.049") than I've seen on typical sissy bars. The rear tire has a low max air pressure. I keep it around 20psi so it absorbs most bumps fairly well. I don't ride it very hard and, I'm a light weight at about 135 pounds soaking wet.

If I were thinking of modifying an existing sissy bar I'd probably cut off the top loop and weld it to legs made from new tubing I bent in a tubing roller. I passed the two legs through the roller at the same time before attaching to a top loop on mine (see the link @kingfish254 added if you haven't already for details). There might be a way to create a bending fixture with wood to do both legs at the same time without cutting off the loop? Filling the sissy bar legs with sand before trying will keep the tubing from deforming too much.

Good luck and keep us posted on your results.
 
Use stainless steel tubing; no cracking and once polished it will look good forever. i always use stainless because i'm way too lazy to polish anything more than once.
 
kingfish254 said:
It's a modern muscle bike. If there was ever a genre of bicycles that screamed artistic sexy curves over efficient structural design it would be the muscle bikes of the 60s and 70s. Artistic flare trumped function every single time. :D
Click to expand...
You mean like the Raleigh Chopper? Pin on Raleigh Chopper (pinterest.com)

Seems like the Sting Rays just used the standard Schwinn Cantilever frame, which had been used for decades prior? I consider the "S curved" tube from head to crank to be the weakest element of this frame design.

Column elements buckle under design loads if flexed too far, as axial compressive loads become moment loads. Using an initially curved element just means that the component must be designed for the bending load. A stronger element is required, therefore more mass. This explains how an element should be de-rated (or section strength increased) for initial curvature. Initially Curved Columns (efunda.com)

I use curved compression elements in designs when I want the structure to be compliant or springy. It definitely has its place.

I understand that art isn't created to meet any practical criteria. But, the best functional objects, in my opinion, are those in which attractive lines and efficient design intersect.
 
Like axeman said, bending your sissy bar tubing will reduce the load it can handle. You’ll need to use thick wall tube to make sure that it will take the load. You won’t be able to use a stock sissy bar and have a safe ride. You will have to make it from scratch.
 
tjwilson said:
Hey that's my bike!
Pretty cool to see someone wanting to do a sissy bar somewhat similar...
Click to expand...

It is an honor to have you respond to my post, TJ. That whole bike rocks.

Based on the degree of difficulty of bending tubing, I may try to do some sort of articulated and suspended sissy bar.
 

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