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Old 03-23-2006, 04:45 PM   #1
scootermcrad
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Default Bending tubing without a bender, just heat

A buddy and I are working on some parts and we need to bend some tubing. We don't have a bender, don't know someone with a bender, but do have a torch and a good place to start bending. We need to bend 1"x.120 wall and 3/4"x.109 wall mild steel tubing. I figured on making something to bend the tubing around and then heating it up just enough to carefully bend it. The bend needs to be more like a slight arc that doesn't have a constant radius and not anything real tight.

Is this going to make the tubing structurally unsafe in the end? Seen it done and used on frame parts, but never done this myself.
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Old 03-23-2006, 05:36 PM   #2
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Default Re: Bending tubing without a bender, just heat

Quote:
Originally Posted by scootermcrad
A buddy and I are working on some parts and we need to bend some tubing. We don't have a bender, don't know someone with a bender, but do have a torch and a good place to start bending. We need to bend 1"x.120 wall and 3/4"x.109 wall. I figured on making something to bend the tubing around and then heating it up just enough to carefully bend it. The bend needs to be more like a slight arc that doesn't have a constant radius and not anything real tight.

Is this going to make the tubing structurally unsafe in the end? Seen it done and used on frame parts, but never done this myself.
Fill the tube with sand, this will help to keep the bend true and not have any flat spots. Take a piece of qtr inch steel or a 2x12 and make a jig using bolts of a good size
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Old 03-23-2006, 05:59 PM   #3
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Default Re: Bending tubing without a bender, just heat

The shape I need to bend it to is sort of elagent but only bends one dirction (sort of parabolic). I figured if I took some plywood and cut it to the contour I wanted I could use that as my guide. If needed I could screw some 1/8" flat bar to the wood (so nothing catches on fire and the wood doesn't give), clamp or bolt the whole shabang to a table and give it a good heav-ho after I've got it nice and hot. Not going to mention where I saw that done , but it seemed to work, but can think of a million ways to improve on the concept to be a little more specific.

I'm mostly concerned about what's going to happen after this thing has been brought up to that temp and cooled off. Should it be cooled fast or left to cool to room temperature? It needs to be strong, but it will get some reinforcement eventually anyway.
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Old 03-23-2006, 06:34 PM   #4
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Default Re: Bending tubing without a bender, just heat

To temper it heat it all up to a nice straw color and quench it
Quote:
Originally Posted by scootermcrad
The shape I need to bend it to is sort of elagent but only bends one dirction (sort of parabolic). I figured if I took some plywood and cut it to the contour I wanted I could use that as my guide. If needed I could screw some 1/8" flat bar to the wood (so nothing catches on fire and the wood doesn't give), clamp or bolt the whole shabang to a table and give it a good heav-ho after I've got it nice and hot. Not going to mention where I saw that done , but it seemed to work, but can think of a million ways to improve on the concept to be a little more specific.

I'm mostly concerned about what's going to happen after this thing has been brought up to that temp and cooled off. Should it be cooled fast or left to cool to room temperature? It needs to be strong, but it will get some reinforcement eventually anyway.
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Old 03-23-2006, 07:02 PM   #5
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Default Re: Bending tubing without a bender, just heat

heating it up and allowing it to cool won't really affect the integrity, let it cool slowly though. i'm assuming its just mild steel and not some higher toughness alloy.
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Old 03-23-2006, 07:26 PM   #6
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Default Re: Bending tubing without a bender, just heat

It's allright to bend it with heat. Do it slowly, and let it cool naturally.
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Old 03-23-2006, 07:44 PM   #7
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Default Re: Bending tubing without a bender, just heat

DO a search over on the HAMB. av8 has done several posts about sand-bending. Kent Fuller bent his FED chassis and front axles this way. Mikes last post about it was a couple years back.
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Old 03-23-2006, 08:09 PM   #8
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Default Re: Bending tubing without a bender, just heat

yeah...

what fuller did was lay his sand out in the sun first to bake off any excess moisture (water expands under heat, making a pipe bomb). tack weld or otherwise secure a cap on one end, take and pack that sand in there TIGHT, like fill, tap, bounce it on the floor end wise, pack it in there REAL good, seal the other end leave a hole for vapor to escape. heat well and evenly and pull GENTLY.

steel wheels of various sizes welded to a table make great bucks for bending.
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Old 03-24-2006, 09:55 AM   #9
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Default Re: Bending tubing without a bender, just heat

Awesome! Thanks guys! I appreciate your input. I will check out the tech stuff on the HAMB also. If I end up doing this I will try to do a quick TECH post for the tech archives so people like me aren't asking silly questions over again.

Thanks guys!
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Old 03-24-2006, 02:28 PM   #10
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Default Re: Bending tubing without a bender, just heat

I've bent thin wall tubing with heat and sand...but it always freaks me out, I drill vent holes to let the moisture out. But it shouldn't be necesary with 1/8" wall tubing, I bend it all the time with heat and something to wrap it around and never get any noticable flatening. I don't think I would quench it to temper it though. Should be fine if its allowed to slow cool. I'd rather have a frame bend on me when abused than break in two.
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Old 03-24-2006, 02:54 PM   #11
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Default Re: Bending tubing without a bender, just heat

I remember seeing somewhere that salt is better than sand to use because of its grain shape. I don't remember what exactly that was all about, but apparently it gives a better bend. I don't really know what I'm talking about, though.
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Old 03-24-2006, 05:06 PM   #12
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Default Re: Bending tubing without a bender, just heat

My welding instructor at school tells us to never quench welds. He says that when i get a job as a welder I could get in huge trouble if I quench welds. The reason why is because when they are cooled fast the metal hardens, but becomes brittle. If it cools slow the metal will slightly return to its prior state. I would say dont quench the bars after your done bending them. let them cool naturally. Better to have the bars bend then to have them snap off when you dont expect it.
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Old 03-25-2006, 12:28 AM   #13
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Default Re: Bending tubing without a bender, just heat

Quote:
Originally Posted by mushmouth
My welding instructor at school tells us to never quench welds. He says that when i get a job as a welder I could get in huge trouble if I quench welds. The reason why is because when they are cooled fast the metal hardens, but becomes brittle. If it cools slow the metal will slightly return to its prior state. I would say dont quench the bars after your done bending them. let them cool naturally. Better to have the bars bend then to have them snap off when you dont expect it.
Sounds right. I know the aircraft guys have gas welded moly for years (way before DIY'ers had access to tig machines) and would stress relieve joints when all the tubes/brackets/gussets were added to a cluster by heating the cluster up w/ torch & allowing to cool as slowly as possible.

And I learned the hard way about quenching a weld on a wrench I bastardized... your welding instructor was right!

-bill
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Old 03-25-2006, 11:36 AM   #14
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Default Re: Bending tubing without a bender, just heat

Quote:
Originally Posted by mushmouth
My welding instructor at school tells us to never quench welds. He says that when i get a job as a welder I could get in huge trouble if I quench welds. The reason why is because when they are cooled fast the metal hardens, but becomes brittle. If it cools slow the metal will slightly return to its prior state. I would say dont quench the bars after your done bending them. let them cool naturally. Better to have the bars bend then to have them snap off when you dont expect it.
My welding instructor even said to bury our stuff in sand to cool it REALLY slowly...
My .02

-Nate
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Old 03-27-2006, 10:37 PM   #15
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Default Re: Bending tubing without a bender, just heat

Quote:
Originally Posted by mushmouth
My welding instructor at school tells us to never quench welds. He says that when i get a job as a welder I could get in huge trouble if I quench welds. The reason why is because when they are cooled fast the metal hardens, but becomes brittle. If it cools slow the metal will slightly return to its prior state. I would say dont quench the bars after your done bending them. let them cool naturally. Better to have the bars bend then to have them snap off when you dont expect it.
He's right. when you quench just welded metal you cause the crystals to stop growing rapidly. This results in smaller grains (especially at the metal surface) surrounded by a hard, brittle substance called Cementite (which has a lot of Carbon in it). This makes the welded material harder but more brittle (the last thing you want in a frame for example).

The process where you quench welding temp material is far different from when you quench steel at relatively low temperatures (less than 300 degrees celsius) as mentioned in the topic earlier. This process is called tempering and is only really suitable for high carbon steels. Tempering is used to create hardness in things like cold chisel blades and wood saws.

You might have seen knife/sword makers temper their knives by quenching. This is how they make their blades hard and able to hold an edge.

You'll also hear some people say that if you lift the flame away slowly you'll remove the stresses in the steel. This is a bit of an old wives tale as well. The process you use when you want remove all internal stresses and maximise it's maleability is called normalising. This involves heating the piece thoroughly to it's upper critical temp (around 800-900 degrees from memory) then cooling it slowly in a furnace over a 24hr period. Naturally you get a great chance of warpage from this so it's a pretty involved process.

Cheers
Scotty
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Old 03-28-2006, 09:19 AM   #16
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Default Re: Bending tubing without a bender, just heat

Quote:
Originally Posted by rigidshovel
He's right. when you quench just welded metal you cause the crystals to stop growing rapidly. This results in smaller grains (especially at the metal surface) surrounded by a hard, brittle substance called Cementite (which has a lot of Carbon in it). This makes the welded material harder but more brittle (the last thing you want in a frame for example).

The process where you quench welding temp material is far different from when you quench steel at relatively low temperatures (less than 300 degrees celsius) as mentioned in the topic earlier. This process is called tempering and is only really suitable for high carbon steels. Tempering is used to create hardness in things like cold chisel blades and wood saws.

You might have seen knife/sword makers temper their knives by quenching. This is how they make their blades hard and able to hold an edge.

You'll also hear some people say that if you lift the flame away slowly you'll remove the stresses in the steel. This is a bit of an old wives tale as well. The process you use when you want remove all internal stresses and maximise it's maleability is called normalising. This involves heating the piece thoroughly to it's upper critical temp (around 800-900 degrees from memory) then cooling it slowly in a furnace over a 24hr period. Naturally you get a great chance of warpage from this so it's a pretty involved process.

Cheers
Scotty
Now THAT'S an explanation!!!!!!! Thanks Scotty! That was very insightlful!

Thanks for all the info guys! I wouldn't have quenched it, but good to know what would happen if I did quench it after welding or heating the tubing. Good for future reference actually!

We're going to build a front end for my buddy's late shovel and the legs will have some bends in them(don't ask). This thread helped out with the design process for sure!

Thanks!
Scooter
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Old 03-28-2006, 09:41 AM   #17
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Default Re: Bending tubing without a bender, just heat

better not to heat it. bend it cold.
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Old 03-28-2006, 11:24 AM   #18
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Default Re: Bending tubing without a bender, just heat

Quote:
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better not to heat it. bend it cold.
That's great and ideal, but I don't have the luxury of having access to a bender or someone with one. If the majority of you are telling me that I'm safe bending 1" tubing with a semi-thick wall, then I'm going that route.

Now, if someone tells me without a doubt that this is dangerous and stupid, then i will find another way or won't build it at all.

Now, is this dangerous and stupid or an appropriate measure to take for a bend that has a varying/non liniar radial dimension??? Getting some mixed answers here now.

Maybe it would help if I said the tube that's going to be bent will also have a support from an adjoining tube or a gusset/rib that will run the full length of the curve.

If someone here knows FOR SURE you can make a bend like this with heat and it will be structurly safe, please speak up. THANKS!!
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Old 03-28-2006, 03:15 PM   #19
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Default Re: Bending tubing without a bender, just heat

nobody can tell you if it's going to be safe. that's going to depend on the design, the loads, the materials, and the quality of the welds. one thing you don't want to fail on a motorcycle is the forks, so if you're in doubt, don't do it.


{QUOTE=scootermcrad]That's great and ideal, but I don't have the luxury of having access to a bender or someone with one. If the majority of you are telling me that I'm safe bending 1" tubing with a semi-thick wall, then I'm going that route.

Now, if someone tells me without a doubt that this is dangerous and stupid, then i will find another way or won't build it at all.

Now, is this dangerous and stupid or an appropriate measure to take for a bend that has a varying/non liniar radial dimension??? Getting some mixed answers here now.

Maybe it would help if I said the tube that's going to be bent will also have a support from an adjoining tube or a gusset/rib that will run the full length of the curve.

If someone here knows FOR SURE you can make a bend like this with heat and it will be structurly safe, please speak up. THANKS!![/QUOTE]
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Old 03-28-2006, 03:54 PM   #20
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Default Re: Bending tubing without a bender, just heat

Quote:
Originally Posted by jw_
nobody can tell you if it's going to be safe. that's going to depend on the design, the loads, the materials, and the quality of the welds. one thing you don't want to fail on a motorcycle is the forks, so if you're in doubt, don't do it.
Actually, I wasn't in doubt until you said something. I have no doubt that the design is strong and as long as the material isn't significantly weaker than it's produced state it will be a great design... but... it's the process of heating something up enough to get a clean bend that concerns me. If it's going to make the tubing significantly weak then I agree it shouldn't be done. I'm looking for hard facts here. Something with an explanation as detailed as rigidshovel's would be great, but not required

jw, if you are telling me that this process will significantly weaken the tubing then I would like you to expand on your answer so it's clear.

I think I need to re-state the question so the bottom line is clear....

Does anyone know if bending tubing using heat and exercising proper cooling will make the tubing (of the sizes mentioned above) significantly weaker?
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