flame straightening

GlennM · Jul 7, 2006

This is Chapter 2 of my previous question about jigs. I purchased a sheet of 3/8" A36 for use as the jig base. So far, this is working nicely, except for one little problem:

The piece (18"x32") I cut for my first jig has a slight crown to it, about 1/8" in the middle. The bow appears to be spread evenly across the plate.

I suspect that the source of the distortion is the kerf from the plasma torch, because the large plate from which this smaller piece was cut does not have a bow in it. Or, I may have released residual stresses by cutting off a piece. It doesn't really matter where the distortion came from; the important thing is to reduce it. This piece is too large for me to put into my shop press.

I have often read of flame straightening, and it seems as if it might be the answer to my problem. I have a rosebud tip for my torch, or I could use my propane weed burner (I use it for preheating items for welding), so I think I can put enough heat into the plate. I can easily rig up a spray wand to blow air/water mist on the plate to chill it.

If anyone has hands-on experience with the flame straightening technique, I would appreciate it if you would share a few tips regarding how to approach the task of flattening the jig base.

I don't need perfectly flat, BTW; I'd be happy to halve the 1/8" bow to 1/16" or less. I'm willing to entertain other suggestions for flattening the plate, too. Bring 'em on.

Thanks,

Glenn M.

pm · Jul 8, 2006

flame straigtening is most applicable when you can introduce some bias into a structure through expansion/contraction ie a tube that has a curve can be straightened by shrinking the outside of the curve. it is often most easy to use well to counteract the distortion caused by welding or other localized forces.

I would not think a handheld torch would lend itself to straightening your 3/8 plate.
I would try mechanical means first - preferably a roller
otherwise you might manage to rig up a series of jacks and/or clamps to overbend it in the opposite direction, but takes skill and easy *#$%@!@#!!! it all up.

as far as using heat you could send it out for relaxing but that would be a bit of an investment.

if I were you I would start with some thicker plate
3/8 is gonna move right away when you weld on it anyway.

boozer · Jul 8, 2006

is it possable to make a sturdy frame for the jig to mount to, like 2" sq. tube, or something? that would pull the alum back down to flat, and also give you the option of shimming areas that need it.

GlennM · Jul 8, 2006

I did flatten the plate. I used an extremely high-tech method. I drove my truck over it.

I put a plywood shim under each end, then drove the truck over the middle. Didn't quite do the trick the first time, so I shimmed the edges up a bit more and drove over it again. That did the trick. Took out pretty much all the bow; the plate is plenty flat for my purposes.

I have already welded on it. I have tacked down the pieces of angle and clamps that locate the tubing. Welding the fixture pieces to the plate had no noticable effect on the plate. These are small tack welds made with a MIG. The plate is barely warm after tacking.

Very little heat is introduced into the plate when welding the tubing because I only use the jig to tack everything together, then I remove the piece and finish welding.

If I were welding larger, heavier pieces that would hold a lot of heat/create a lot of stress, or if flatness were really critical (like with Bob's train bridges) I would use much thicker plate. Then the problem would be moving it around.

I'm not puny, but neither am I Gonad the Barbarian. A slab of steel 3/4" or 1" thick and 18"x32" is not something I can move without help or a hoist. I don't want to mess around using an engine hoist to move these jigs unless it is absolutely necessary.

-Glenn

pm · Jul 8, 2006

"..I drove my truck over it..... then, drove over it again ... Took out pretty much all the bow; the plate is plenty flat for my purposes...."

I like it !

jackalope · Jul 8, 2006

Is there any reason you cannot make a frame on the underside out of some thick rigid material. By welding the 3/8" plate to a frame, of sorts, you could basically hold the plate into a straight plane.
Since it is only a welding jig plate and it doesn't sound TOO critical, the truck trick would likely fix the problem....For now.

jackalope · Jul 8, 2006

Probably one of the most trick welding tables I have seen was at this old fab shop where a guy had an OLD milling table with "T"-slots. The table weighed several tons and was like 6ftx10ft and several inches thick. All cast iron. I asked him how the hell he got it where it was located and he said, "you DON'T want to know....but I can assure it will NEVER mover again!"

--Grant

stephen thomas · Jul 8, 2006

sounds more like a floor plate. I've been at auctions where you could have bought a set of floor plates for a good bit less than the scrap price....if there was a place to put them and you could afford the rigging.

Which brings to mind a thought: wonder when the last large floor plates were made & machined in the USA? Or does someone still pour and machine them?

smt

Captain · Jul 8, 2006

Hello,

I work for a structural fabrication shop cutting plate. We fabricate large buildings and factories and do a lot of flame straightening. The process is low tech, but requires some skill and experience in practice. Simply heat the "high spots" red hot and let them air cool. The steel contracts upon cooling past the original shape. Repeat the process until the high spots are gone, or gone enough. In practice it requires a bit more skill. The guys I work with can look down a 80' beam, walk down it chalk-marking as they go, and end up with a distortion free beam after one try. I'm talking 20+ years of experience in some of these guys. As far as my limited experience, I am always amazed at how much stress is in structural shapes. I have to be very carefull not to get pinched or slapped as I cut. The thinner plates distort much more than the thicker, sometimes from stresses introduced by just moving the plate around. Occasionally, chain binders and weights are required to hold the plate down to complete the cut, especially on long cuts. Welding stresses only complicate the whole process. I have so much to learn!

GlennM · Jul 9, 2006

"I have so much to learn!"

Don't we all? The only difference among us is that some folks are a little farther along than others. A friend of mine, an experienced and talented engineer, says he wants his epitaph to read "Oh, no, not another learning experience!"

There is a book I'm hoping to find, which unfortunately is out of print: "Flame Straightening Technology for Welders" by John P. Stewart. If anyone has a copy they'd part with, or knows of a copy, please let me know. I would pay up to $50-$60 for this book in any condition, so long as it's readable.

Ries · Jul 9, 2006

I have a copy of the John P Stewart book- in fact, I have copies of both his books- his other one, "Distortion Control" is pretty good too. But I aint selling- I buy books, and hoard em like a dragon. Its part of my long term plan of revenge on my children.
Maybe sometime you can come by and xerox it. Kingston aint far- in fact, I just brokered a deal to sell the 40 acres next to me to a friend from Kingston, who considers Kingston to be too overrun with surburbanites for his taste.

At the fall NWBA (Northwest Artist Blacksmith Association) conference in Mt. Vernon, we had a demonstrator come down from Canada who did flame straightening in industry for 50 years or so. He uses a compressed air line and a hose, both feeding into one homemade nozzle, to blow high pressure water on, or right next to , the heated areas. He bent an 8" I beam into about a 10 foot radius with just a rosebud and this hose, with nice even curvature.

But this technique is an art, not a science, and it takes a lot of practice. After your 4th or 10th piece of 3/8" plate, you would probably get pretty good at it, but it isnt really the kind of thing you can reliably use to fix one part, and get it right the first time.

Plate is the hardest thing to control the heat movement of, as well- big beams, pipes, and angles are all easier, strangely enough.

GlennM · Jul 10, 2006

Edison is up around Bellingham, right? I have some motorcycling buddies up there. Next time I'm up that way I'll try to drop by.

I will make a sincere attempt to find the book before I copy it. Copyrights and all that. I've found another lead on Stewart's books. Seems that they're self-published, and he is in Canada. So if I try to contact him and that falls flat, then I'll take you up on your offer to copy the book.

Ries · Jul 10, 2006

I dont think he is a member of the electronic generation- no email or website- but here is his address from his book.

John P. Stewart
233 Dupras Avenue
LaSalle Quebec
Canada H8R3S4
514-366-8410

I bought mine direct from him, quite a few years ago.

tinman13 · May 18, 2018

I realize this is a long dormant thread but John Stewart still has books available!
ORDER FORM - FLAME STRAIGHTENING AND DISTORTION CONTROL

morestainless · May 19, 2018

I've straightened a 1/4" bowed iron sheet using a ball peen hammer on the concave side.

Chip Chester · May 19, 2018

I tried the truck method with some 9/16 steel sheet. 2500 Suburban. Cement block to make a 5' long ramp. Drove up, and it laughed at me. The steel, that is. Still just as bent. Quicker to grab a fresh sheet...

DDoug · May 21, 2018

tinman13 said:
I realize this is a long dormant thread but John Stewart still has books available!
ORDER FORM - FLAME STRAIGHTENING AND DISTORTION CONTROL

$65 for 102 pages ?

Some real life feedback (like from Ries, who owns the book) is in order I should think.

Clive603 · May 21, 2018

digger doug said:
$65 for 102 pages ?

If it saves you three hours of shop time, including reading allowance, I figure you are already ahead.

Not gonna admit how many hours I've wasted trying to get "Hey that looks simple" stuff I don't really understand working properly. Sort of nearly but not quite is usually pretty easy but getting it to behave well is different.

Finally got old enough and sensible enough to buy the book before diving in. Not that I shall ever do flame straightening so that one is off the list.

Clive

Rob F. · May 21, 2018

I have at least one of stewarts books and his background was heavy shipbuilding and such. talks alot about how to straighten 2" plate and thick things like that. Thinner plates like 3/8 do not have the thickness to use his methods easily. Simply put use the smallest, hottest flame you can to heat one side of the plate. The heated side needs to get red hot and be cooled before the opposite side gets hot, so the one surface of the plate will shrink and pull the metal into shape. I have not needed to use them for a few years so my memory may be rusty.
It is good info in the books, especially for thicker materials.

DDoug · May 22, 2018

Clive603 said:
If it saves you three hours of shop time, including reading allowance, I figure you are already ahead.

Not gonna admit how many hours I've wasted trying to get "Hey that looks simple" stuff I don't really understand working properly. Sort of nearly but not quite is usually pretty easy but getting it to behave well is different.

Finally got old enough and sensible enough to buy the book before diving in. Not that I shall ever do flame straightening so that one is off the list.

Clive

Rob F. said:
I have at least one of stewarts books and his background was heavy shipbuilding and such. talks alot about how to straighten 2" plate and thick things like that. Thinner plates like 3/8 do not have the thickness to use his methods easily. Simply put use the smallest, hottest flame you can to heat one side of the plate. The heated side needs to get red hot and be cooled before the opposite side gets hot, so the one surface of the plate will shrink and pull the metal into shape. I have not needed to use them for a few years so my memory may be rusty.
It is good info in the books, especially for thicker materials.

And yet, still no yes or no on the value of the book ?

Have either of you used (with success) any of the techniques that are unique
in that book ?

flame straightening

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