Bending a spring steel rod to shape and heat treat, DIY?

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  • #1
Spinnor
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There used to be sold a style bicycle handlebar bags that used what I think is a formed spring steel rod that fit over the handlebars and looped under the handlebar stem that supported a handlebar bag. For whatever reason this style does not appear to be available any more. I think it is a superior design and would like to reproduce roughly the shape seen below. The metal rod frame appears to be spring steel, you can squeeze the ends together a fair amount and it returns to its original shape when you let go. I could easily bend the same size rod to the shape I want if the steel was soft but after it is bent it seems it must be heat treated to give it strength and springiness? Does that seem how the handlebar bag frame below might have been made, form and then heat treat or do you just form the spring steel and you are done? Assuming the frame must be heat treated how difficult would that be? Pictured below is a bag frame that I have bent, sometimes with heat, too many times to fit different bikes and bags.

Thanks for any suggestions on steel type and heat treatment.

1602722492676.png



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1602723970400.png
 

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  • #2
jrmichler
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Spring wire up to some size can be bent cold. The photo below is my first attempt at winding a replacement spring for a trash pump mechanical seal:
Spring.JPG

It was cold wound from 0.125" diameter stainless steel wire. I got the wire from McMaster-Carr: https://www.mcmaster.com/stainless-steel-wire/spring-back-multipurpose-304-stainless-steel-wire/. This wire can be cold bent to a much tighter radius than in the above photo.

Warning: When bending spring wire in these sizes, be careful about releasing tension. If you cut it under tension, you can get an impressive snap back. Ask me how I know this.
 
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  • #3
Baluncore
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For whatever reason this style does not appear to be available any more.
I am not surprised they are no longer available.
You need to close the gap between the points to make it safer.

There are a couple of problems with that forward mounted design. Firstly, depending on height, in a collision they may injure a pedestrian or another cyclist, like the horns of a bull. Secondly, as the rider goes over the handlebars, they may be injured by the upward pointed rippers.
 
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  • #4
Spinnor
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My wire frame is almost exactly 1/4 inch in diameter. Unfortunately the McMaster Carr rod in your link only goes up to .162 inches which might be pushing the rods limit.

When new the frame supported a bicycle touring bag that could probably hold 8 pounds with ease. I never carry that much, tools a snack, light clothes, phone.

McMaster Carr has a lot of rods! Might this work,

https://www.mcmaster.com/steel-rods/tight-tolerance-multipurpose-oil-hardening-o1-tool-steel-rods/

Sizes above and below .25 inches and in 36 inch lengths and not too expensive.
 
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  • #5
Spinnor
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I am not surprised they are no longer available.
You need to close the gap between the points to make it safer.

There are a couple of problems with that forward mounted design. Firstly, depending on height, in a collision they may injure a pedestrian or another cyclist, like the horns of a bull. Secondly, as the rider goes over the handlebars, they may be injured by the upward pointed rippers.
I ride very cautious when around people and in a region where there are not many people. I have ridden for more than 40 years and really only went down bad twice, once in a pack and once in snow. Shook it off and on my way in my 20's and hobbled back home in my 60's. I will be even more careful now with the picture of me impaling a walker or myself on the local bike path in the back of my head.

Because of the design the wire frame would probably give and rotate back and up before doing much puncturing but I get your point, I will be more careful.

Could easily add a round plastic ball to the pointy ends to make it more safe or bend the end into a circle of sufficient radius.
 
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  • #6
Spinnor
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  • #7
Baluncore
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I will be even more careful now with the picture of me impaling a walker or myself on the local bike path in the back of my head.
One fellow was riding along carefully on a dirt road when he went over the bars. Unfortunately, on the way over, he snagged the handle on the bell, and lost his trousers. There he was on the side of the road, torn all the way along his dorsal shaft, and holding on tight to staunch the blood. A kindly woman from a nearby cottage approached to render assistance, only to be confronted by a rapidly growing problem. She must have had extensive medical experience to handle that situation so calmly. He was stitched up in hospital later, so after all, it had a happy ending. He told us the story over lunch one day, and offered to show us the scar. We declined.
 
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  • #8
berkeman
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Spring wire up to some size can be bent cold. The photo below is my first attempt at winding a replacement spring for a trash pump mechanical seal:
View attachment 270971
It was cold wound from 0.125" diameter stainless steel wire. I got the wire from McMaster-Carr: https://www.mcmaster.com/stainless-steel-wire/spring-back-multipurpose-304-stainless-steel-wire/. This wire can be cold bent to a much tighter radius than in the above photo.

Warning: When bending spring wire in these sizes, be careful about releasing tension. If you cut it under tension, you can get an impressive snap back. Ask me how I know this.
That is so cool. I have a couple of custom springs that I'd like to wind up. What kind of tools and setup did you use?
 
  • #9
anorlunda
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If you search "DIY coil springs" you'll find lots of hits.
 
  • #10
berkeman
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But, but, you're not going to spoonfeed me? I have to go look it up?! Sheesh! :wink:
 
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  • #11
jrmichler
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Springs made of 0.125" wire are more challenging than those made from smaller wire. Here's my setup:
Spring Winder.jpg

The wire is clamped to the mandrel with a cross drilled bolt. Back tension is a UHMW clamp block. The lathe is run at the slowest back gear speed, 60 RPM. Coil pitch is by hand feeding the carriage travel, which is how I got the closed ends on the mechanical seal spring. One hand on the power switch, the other hand on the carriage travel handwheel. And be very careful to remove the tension before cutting the wire.

I would use the power feed for longer springs with 4 or more turns per inch.
 
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  • #12
Twigg
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My advice is to find the nearest person who can weld and bribe them with a box of donuts. Use multiple pieces straight mild steel stock and weld it to the shape you want. Don't bother with stainless unless your buddy happens to be a serious welder (not the weekend welder type) and has a TIG machine. I'd avoid high carbon steel (O1, for example) because welding such small round stock would probably make it super brittle and snap right off on the first crash. Mild steel will rust, so spray paint over the exposed metal. Whatever you do, DON'T buy one of those $100 welders off the internets. They are useless and you will regret it. I sure do :cry:

If the piece bends all over the place after the welding, use a propane torch and some pliers to persuade it. It'll move much easier than stainless or O1.

"Heat treating O1 tool steel is simple. In short, bring it to critical temperature, quench it in vegetable oil, then temper it in an toaster oven or regular kitchen oven for one hour at 400˚. " But is it the right type of steel?

https://www.popularwoodworking.com/woodworking-blogs/heat-treating-o1-steel/

"How Fast Do You Have to Quench? Hardenability of Steel"

https://knifesteelnerds.com/2019/02/25/how-fast-do-you-have-to-quench-hardenability-of-steel/
I will be very surprised if you can bend 0.25" O1 rod cold. I've never tried it (on account of me being built like a twig and knowing my limits), but I assume what you get from the McMaster stockroom will be normalized: pretty tough and fairly brittle. If you intend to try it with cold O1 rod, use a vise and pliers not bare hands and protect yourself from flying metal if it breaks.

Overall, I don't think you want to go the O1 route. You are going to have a really hard time bringing that whole shape to critical temperature. Critical temperature is somewhere between red and orange hot (depending on your lighting and the steel). The problem is, if you use a MAP gas torch, by the time you get one 4" segment of the bent rod arrangement to temperature, the rest will have cooled off. If you know a plumber who'd be kind enough to attempt heating it with an oxy-acetylene torch and a rosebud tip, you might have a fighting chance if you also built a shell for it out of bricks to trap heat.
 
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  • #13
Spinnor
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I am guessing that in the manufacturing process of the part I am trying to reproduce it is bent cold and then batch heat treated? I just need the right type of spring steel rod. I have a flame weed eater that produces a lot of heat. Heat treating the rod would be the hardest part of the project but doable with enough precisistance? It looks like after heat treatment the part should also be stress relieved at around 400F for an hour? If the O1 steel was too hard to bend cold it could be heated with another torch I have for bending though I don't know if heating it for bending purposes would affect the properties of the steel with regard to the final heat treatment.

Thanks.

1603192347507.png
 
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  • #14
Spinnor
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Got some 1/4 inch O1 oil hardening steel rod from McMaster Carr Friday. Sunday I got out the weed eater torch,

1603648160991.png


With a reference mark in the center of the rod the center 6 inches of the rod were heated and then bent in one motion around a bicycle/stem form,

1603648257817.png


Minor tweaking of frame was done cold. Further bending was done by heating rod locally with an acetylene torch,

1603648324976.png


Final product,

1603648394637.png


Frame seems strong enough for the time being, when bored might try heat treating the frame. If one divides the weight of the frame and bag by its weight capacity (factory made bicycle handle bar bag and frame like the one above) one gets a pretty small number, smaller then any other system I believe. That for me makes it a superior system, safety hazard aside.
 
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  • #15
Tom.G
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Well, I hope you never do a header over the handlebars with that. It could open you up like you had a zipper from sternum to crotch.

Ride safe!
 
  • #16
Spinnor
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After I paint the frame will wrap enough electrical tape around the ends to reduce the likelihood of that event,

Drive safe!
 
  • #17
Baluncore
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Rather than only 90°, I would wind between 270° and 360° at the horns
That would reduce the gore liability, and hold a bag more securely.
 
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  • #18
Spinnor
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Rather than only 90°, I would wind between 270° and 360° at the horns
That would reduce the gore liability, and hold a bag more securely.
Why not just a good wrap of electrical tape?
 
  • #19
Baluncore
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Why not just a good wrap of electrical tape?
In time, electrical tape will slide off, or be removed by someone who does not know why it is there. Safety features should be permanently built into a design, not added with duct tape as an afterthought.
 
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  • #20
Spinnor
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This frame is for my use only, I am not going into production. If someone were to resurrect this design I concede that my frame as is would need to be made a bit safer.
 
  • #21
Baluncore
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This frame is for my use only, I am not going into production.
You are assuming it will not be ridden by a friend, or inherited after your sad demise.
Do you intend the "built in" risk to be a surprise punishment for the thief, or for the naive purchaser of your stolen property?
 

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