pinchvalve SuperDork
Oct. 28, 2009 8:56 p.m.

I have to straighten out some bent metal. Think, cargo rack on an ATV and you will have the thickness and size of the tubing I want to bend. I know that straight propane will never get it hot enough, is there a readily available alternative that uses the same hardware? MAPP gas?

Toyman01 HalfDork
Oct. 28, 2009 9:04 p.m.

Do you have a turkey fryer? The burner on most of the will get plenty hot enough to soften steel.

Schmidlap Reader
Oct. 28, 2009 9:24 p.m.
pinchvalve wrote: is there a readily available alternative that uses the same hardware? MAPP gas?

I asked this question at Home Depot a couple of weeks ago. The plumbing guy told me that a MAPP cylinder will work with the propane torch, but it won't get as hot as a with the dedicated MAPP torch. I went for the dedicated MAPP torch, so I don't have any experience to back up what he said. I also don't know if MAPP will get hot enough to soften the metal adequately.

Bob

Toyman01 HalfDork
Oct. 28, 2009 9:35 p.m.

Mapp gets HOT with O2 but the O2 tanks don't last long, like minutes.

JoeyM Reader
Oct. 28, 2009 9:36 p.m.
pinchvalve wrote: I have to straighten out some bent metal. Think, cargo rack on an ATV and you will have the thickness and size of the tubing I want to bend.

Ooohhhh.....that will be difficult with tubing. Thin solid rod works OK with mapp gas....I made the prop rod for my geo's hood from 1/4" rod.

The problem is that tubing tends to kink/crimp when you heat and bend it. You may want to fill it with sand before trying this....the internal support can reduce the amount of crimping. Also be sure to heat it equally on all sides at the bend site....heating one side less than another can cause crimping.

I'd say that you should see if somebody local has a bending rig.....

cwh SuperDork
Oct. 28, 2009 10:25 p.m.

I really think you would be better off using mechanical force. A bottle jack and a simple fixture to apply force to the bent sections. BTDT.

foxtrapper SuperDork
Oct. 29, 2009 4:32 a.m.

A cargo rack on an ATV? Just bend it. 2x4 should do the job.

If you've got a propane torch and you're determined to use heat, get a map gas cylinder for it.

splitime Reader
Oct. 29, 2009 6:15 a.m.
JoeyM wrote:
pinchvalve wrote: I have to straighten out some bent metal. Think, cargo rack on an ATV and you will have the thickness and size of the tubing I want to bend.

Ooohhhh.....that will be difficult with tubing. Thin solid rod works OK with mapp gas....I made the prop rod for my geo's hood from 1/4" rod.

The problem is that tubing tends to kink/crimp when you heat and bend it. You may want to fill it with sand before trying this....the internal support can reduce the amount of crimping. Also be sure to heat it equally on all sides at the bend site....heating one side less than another can cause crimping.

I'd say that you should see if somebody local has a bending rig.....

If sand is used... it MUST be very very dry. Like bake it in batches to dry it fully out. This is mainly if you use it inside pipe and cap ends to do some DIY adjustments/bending. DRY SAND....

Tetzuoe Reader
Oct. 29, 2009 7:29 a.m.
splitime wrote: If sand is used... it MUST be very very dry. Like bake it in batches to dry it fully out. This is mainly if you use it inside pipe and cap ends to do some DIY adjustments/bending. DRY SAND....

this sounds like an "ask me how I know"

Dr. Hess SuperDork
Oct. 29, 2009 8:36 a.m.

I experimented with sand bending. My conclusions were that if I had about $10K worth of tubing to experiment on, I could get my technique down to where I could do it.

I've used a MAP gas cylinder on a propane torch before. I guess it got hotter. I have oxy/acetelyne now, so I only mess with the little propane torch when I need something bigger than a lighter and smaller than the real torch.

cwh SuperDork
Oct. 29, 2009 3:19 p.m.

That's why the Oxy Acetelyne is called the Big Red Wrench.

NYG95GA SuperDork
Oct. 29, 2009 5:23 p.m.

All the posts have been about bending tubing; straight to curved. But the OP said is that he wanted to straighten already bent tubing, which in my expeirience is a whole dfferent ball game. I'm not certain how much it affects steel tubing, but I have bent a lot of copper tubing over the years, and I've learned that while making the initial bend, a certain amount of heat is generated, slightly changing the anealment properties of the metal. When you try to straighten the same bend out, it requires noticably more pressure to do, and rarely comes out just right.

Take a fresh roll of copper tubing, lay it on a flat surface and roll out while holding the end down. You now have a straight length of copper. Hand bend it in the middle as well as you can without crimping, hoping you got the angle you were going for.

Now use the same pressure to straighten it back out..

Like I said: Whole different ball game.

JoeyM Reader
Oct. 29, 2009 6:26 p.m.
NYG95GA wrote: All the posts have been about *bending* tubing; straight to curved. But the OP said is that he wanted to *straighten* already bent tubing, which in my expeirience is a whole dfferent ball game.....When you try to straighten the same bend out, it requires noticably more pressure to do, and rarely comes out just right.

Good point. The initial bend work hardens it. Straightening it - if that is even possible - probably requires annealing the tube first.

Here's another idea how the OP might be able to straighten it. :

1) a smaller tube that can fit inside the larger one....preferably a smaller tube with an outer diameter that is just slightly smaller than the inner diameter of the bent tube.

2) Soften the bent tube with oxyacetylene until it is flexible.

3) insert a straight length of the smaller tube so that the bent one straightens.

4) withdraw the smaller tube.

Spinout007 Reader
Oct. 29, 2009 8:10 p.m.
JoeyM wrote:
NYG95GA wrote: All the posts have been about *bending* tubing; straight to curved. But the OP said is that he wanted to *straighten* already bent tubing, which in my expeirience is a whole dfferent ball game.....When you try to straighten the same bend out, it requires noticably more pressure to do, and rarely comes out just right.

Good point. The initial bend work hardens it. Straightening it - if that is even possible - probably requires annealing the tube first.

Here's another idea how the OP might be able to straighten it. :

1) a smaller tube that can fit inside the larger one....preferably a smaller tube with an outer diameter that is just slightly smaller than the inner diameter of the bent tube.

2) Soften the bent tube with oxyacetylene until it is flexible.

3) insert a straight length of the smaller tube so that the bent one straightens.

4) withdraw the smaller tube.

That's how we bent the heater pipe on our challenge miata a few years ago. go slow and make sure it stays red, not enough to melt it just make sure the area stays glowing red.

arren
arren New Reader
Oct. 29, 2009 11:20 p.m.

Hello to all

If the peg is a round metal one, these can often be bent back to shape by hand, or bending them over your leg. Failing that, in the field, get a flat rock and put the peg on it - so the bent bit is pointing upwards and use another rock to tap them straight again - you'll figuer out how easily. At home do the same method usig a hammer and solid surface under the peg.

If the peg is a 'V' shape then it you cant easily bend them straight by hand and you will need to bend them over something to get them nearly right. They very rarely will bend straight again but will be good enough to use. When you get home try hitting them with a hammer to straighten them (flat side on something hollow and tap them where the bend is)

Thanks for sharing

Have a nice day

NYG95GA SuperDork
Oct. 29, 2009 11:54 p.m.

Use rocks to straighten out tubing! Why didn't I think of that right away? Plenty of V-shaped tubing out there.

foxtrapper SuperDork
Oct. 30, 2009 5:11 a.m.
NYG95GA wrote: All the posts have been about *bending* tubing; straight to curved.

Nope. Some of us read what he asked. And since he specified "think ATV rack" some of us figured he wasn't interested in perfect straightening, just "good enough" straightening.

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