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Heat shrinking 16ga metal

Discussion in 'The Hokey Ass Message Board' started by Jalopy Jim, Apr 25, 2012.

  1. Jalopy Jim
    Joined: Aug 3, 2005
    Posts: 1,867

    Jalopy Jim
    Member

    I have a question for those with more knowledge about metal working than I have.

    I built my own pick up box ( see Miss Fortune build ) . I used 4-1/4 tubing for the bed rail and 1-1/2 16 ga tubing for the stake pockets and frame between the two sides. The problem I have is I have three bulges in the side. One outward in the center and two inward on the ends of the box. What sequence would I use to straighten the sides. And a lesson in how to heat shrink metal would be nice also.

    thank you for your help, I am self taught via the HAMB and Metalmeet on metal working.

    Jim H:confused:
     
  2. Heat > here (>( does this l l

    You are shrinking a tube so you need the same top and bottom as well as the side .
     
  3. Jalopy Jim
    Joined: Aug 3, 2005
    Posts: 1,867

    Jalopy Jim
    Member

    The sheet metal side is where the oil caning is, the tubing framework surrounding the side is straight .
     

    Attached Files:

  4. Well your post explains in detail the tubing, easy mistake.

    You have oil cans in the middle because you have shrinkage around the perimeter where you welded.
    Is it dead flat sheet or did you roll beads into it ?
    Can you stretch it back by hammer and dolly on or near the welds?
     

  5. pimpin paint
    Joined: May 31, 2005
    Posts: 4,937

    pimpin paint
    Member
    from so cal

    Hey Jim,

    Without seeing a picture, my wag says that you actually need a stretch, and not so much a shrink! Anytime you weld metal it contracts upon cooling. The bulged area in the middle of your panel may well have resulted when the two outter ends contracted? I'd try and put the side panels under tension with a 4 ton Porta-Power, and see if the bulges relax. If so, stretch those areas that have moved whyle under tension.
    If you just start landing shrinks on the areas of the panel that look/feel high/above normal contour, you'll probably pull straight metal from other areas of the panel,and create more damage.:(:(

    " Humpty Dumpty was pushed "
     
  6. metalfaber
    Joined: Feb 2, 2011
    Posts: 218

    metalfaber
    Member
    from Nebraska

    Is this picture showing what you are talking about? Also, are the edges bent at 90 and then plug welded to the tubing, or is it just laying on top of the tubing and welded on the edges?

    More than likely if I understand correctly, when you welded around the panel, all of that area shrank slightly, and is putting pressure on the panel creating the bulges. So you may need to shrink the interior of the panel to get it back to Normal tension.

    What do you have for shrinking equipment? Torch, Shrinking Disc, etc?

    Im assuming that you want to keep it flat with no body lines or beads in it?

    Brian
     

    Attached Files:

  7. Jalopy Jim
    Joined: Aug 3, 2005
    Posts: 1,867

    Jalopy Jim
    Member

    It started as a flat sheet with a 1" flange 45 degree brake at the top.
    I welded the top tube first plug welding through 1/8" holes in the sheet stock spaced about 1" apart.
    Next I welded the bottom frame 1-1/4 tubing again MIG welding plug welds.
    then welded the front panel and finally the stake pockets on the out side. All using a MIG and plug welding.
    One all assembled I seam welded using .023 wire in my MIG and 1/2 " sections at a time.
    and finally clean up the welding using a 1/4 carbide ball burr in the inside corners and grinder on the flat surfaced moving around to keep the heat down.

    does that help??
     
  8. Jalopy Jim
    Joined: Aug 3, 2005
    Posts: 1,867

    Jalopy Jim
    Member

    I have an Torch, but could buy a shrinking disc if that works better. and my previous post explains how I got to this point. and I want the panel flat as possible
     
  9. metalfaber
    Joined: Feb 2, 2011
    Posts: 218

    metalfaber
    Member
    from Nebraska

    Both Vicky and Pimpin replied while I was working on the picture.

    Pimpin, Im probably just misunderstanding you, but Stretch the areas that moved while under tension?? I am picturing the area that has not shrank like the outside has, to move and pull tight when tensioned, correct? If this is so, Im not sure you would want to stretch that area more, as it would bulge further, correct?

    Like Pimpin says if you can stretch the weld area, thats great, but Im assuming it is on the tubing, and this is making it not easily doable.

    If it is bent and plug welded like I was asking, if it is not tight around the edges, you can tap it away from the center of the panel on the corner of the 90 degree bend, to pull it tight, but it may already be tight, or you may not be able to get enough pull from that method.

    The porta power thing could work if you could in a sense stretch the tubing just enough to stetch the edges back to normal, to the relax the sheetmetal, but Ive never done that one, so I couldn't tell you, in theory maybe, in real life, i dunno. :p

    Brian
     
  10. Looks to me like the sides, facing up and down in the pic took the worst of it.
    The edge is really distorted from the welding.

    Jim, it would be very easy to do more damage and cause more work by shrinking the good metal to match the shrunken metal from welding. Right now, the problem is the perimeter shrinkage, correcting that by causing equal shrinkage to the center might not be the right approach.

    Better pics would help. If you can get your dolly up tight to the structure and hammer on the others side , as close as you can to the welds that should relax the center.

    Another option would be to form some beads on the sides, that will make the centers smaller by eating up the metal effectively shrinking it.

    Putting a few heat shrinks will tighten up the oil cans but cause more waves.
    Several dozen smaller ones will be less wavy, several hundred even smaller even less.
    A shrinking disk in a systematic pattern may give you your best results if you choose to shrink it.

    There was also a pretty good tech a few months back about sand blasting. As scientific and controlled as I've ever seen. The warpage from sand blasting is actually from shrinkage, contrary to the common belief that its from heat. An even blast just might do it.
     
    Last edited: Apr 25, 2012
  11. metalfaber
    Joined: Feb 2, 2011
    Posts: 218

    metalfaber
    Member
    from Nebraska

    Im trying to follow, but Im not the best unless I see it in person, sometimes which it is still difficult, but basically, you didn't start with a frame and then weld in the sheet, you welded in the sheet and made the frame in the same process.

    Did you notice when it started bulging the most? Im guessing when you you went back and welded the seams as in my understanding, this resulted in a solid weld around the entire panel. Correct?

    If so, you may need to shrink the center, as stretching the perimeter may not be possible. If so, dont do a little here, and a little there, as the panel started out flat. Come up with a plan to follow, so you evenly shrink the panel, instead of randomly shrinking it, like make some lines, probably from the corners in like an X, and then maybe like a + sign, and visualize the metal pulling together along those lines, little by little. It will tighten up the entire panel with the exception of the untouched areas in between the lines, which you can go back and shrink them slightly if more is needed after following your lines.

    Dont try to work a large area with the torch or shrinking disc, as the shrinking relies on the cool surrounding metal to resist the expansion that is trying to occur while you are heating it, and if you heat too large of an area, your heat will soak into everything and not allow the working area to be contained.

    Shrinking can be done with both a torch or a shrinking disc. Sometimes one method works better than the other.

    Brian
     
  12. metalfaber
    Joined: Feb 2, 2011
    Posts: 218

    metalfaber
    Member
    from Nebraska

    Can you point me to that article, I would like to read it. I have experimented with it myself, and agree that it is not from heat, but I don't believe it causes shrinkage, I believe it causes stretching from a million little hammers hitting the surface and stretching the metal.

    I have effectively used sandblasting on a roof to remove rusted pits while "blending" out my harder blasting and using the shrinking disc in fine tuning after done blasting to end up with a roof that was sandblasted and clean, and needed very minimal filler.


    Jim, in case you are not familiar, or another reader is not, with restretching the weld area as he is talking about, when you weld in a patch panel in sheetmetal, your weld seam will shrink. In order to get it back to how it looked when it was just tacked into place, you just need to hit hammer on dolly on the panel to stretch the welded "HAZ" (heat affected zone) back out to its original position. When doing something like this, shrinking above and or below the welded area may seem like the thing to do, as it may appear to be bulging, but in reality, the only area making the panel out of wack, is the HAZ, and shrinking or hammering out of that area will make it more difficult to get the panel back to normal.

    So...usually yes you want to stretch your weld area back out to repair undesired affects that came from welding. In this case, Im not sure that is going to be possible, so you may have to compromise and shrink the inside of the panel to get it as straight as you can.

    In hindsight, or for next time, another option could have been to make your frame, and then build your panel to fit inside, and then plug welded it minimally, but sufficiently, and then used seam sealer to fill your seams if desired.

    Brian
     
    Last edited: Apr 25, 2012
  13. It here on the HAMB.

    http://www.jalopyjournal.com/forum/showthread.php?t=658008&highlight=sandblasting+damage
    Just a few months ago. He used a 55 Chevy deck lid.
    The blasted surface was measurabely smaller than the inside non blasted side of it.
    Apparently, the texture from the blasting shrinks the metal much the same way a slap file does. But because the metal only get it on one side the overall effect is different on the piece as a whole.
     
  14. F&J
    Joined: Apr 5, 2007
    Posts: 13,222

    F&J
    Member

    Glad I don't have to fix that :)

    Just me maybe, but you should not have done full welds when attaching the skins to the framework. Punched or drilled holes, then plug welded on high heat, to act like factory spot welds, would have worked fine....just like the factory would have done.

    This is the way I build 16ga beds, and I never have used a full weld...ever. I also never use any metal framework heavier than the skin. When you are plug welding thin skin to heavy framework, much hotter welds are required to get any penetration into the heavy metal. Car companies have never used heavy metal framework on pickup beds.

    You can see the short edges are warped to heck, and that shows that the long welded seam has shrunk.

    My advice is to get the torch and practice on those lower short skirts. You will be working small areas without messing up the already warped large sections, because the framework will be a barrier.

    When you keep practicing enough to get both side skirts nice, then you should have more skill level to at least try the large panels. But from here, I'd say those big panels will be a bitch to get straight enough for finish paint. They are just too large of an open area that is unsupported, IMO.
     
  15. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,471

    Rusty O'Toole
    Member

    Shrinking a flat surface, and keeping it flat, is practically impossible especially for your first attempt.

    How bad is it? Is it something you can live with?

    If not you may have to remove the sheet metal and start over. This time use panel adhesive instead of weld.

    Or, give the panels someplace to bulge as by creasing the panel diagonally corner to corner in an X . Or doing vertical stiffening ribs.
     
    Last edited: Apr 25, 2012
  16. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,471

    Rusty O'Toole
    Member

    Are you going to bolt a fender on the side? If you do the bulges may "disappear" or at least not be too noticeable.

    It all depends. If this is a show truck the bulges could be a problem, but not if it is a work truck. You have to use your own judgement.

    I will say, defects that stick out like a sore thumb to you will never be noticed by the average person. Unless you are going for the 100 point restoration or show car look.
     
  17. I just built a new wood stove for the garage. I used self drilling self tapping screws to attach the sheets to the 1-1/2" angle frame. Then I ground the heads off of the self drilling self tapping screws. I had no warped flat sheets. The stove was 18" x 24" x 24".
    Some of the sheets were a little warped when I started. They were cut by a plasma cutter. I clamped the sheets with c-clamps to the pieces of angle and started screwing.

    I placed the screws on 1-1/2" centers and worked from one end to the other. I also started in the middle of the sheet and worked towards both edges.
     
  18. metalfaber
    Joined: Feb 2, 2011
    Posts: 218

    metalfaber
    Member
    from Nebraska

    I read that thread, and they are saying what I thought, that the sandblasting caused stretching of the panel, if you read it in its entirety. One portion in there could cause a misunderstanding very easily, but if you read carefully, that area is talked about again towards the end.
     
    Last edited: Apr 25, 2012
  19. 51 Henry J
    Joined: Nov 21, 2011
    Posts: 20

    51 Henry J
    Member

    Without putting my hands on the metal, and getting a feel of what the metal is doing, I hesitate at offering a solution to your problem.

    That being said, it appears (from the picture) that you have skip welded along the tubing while the 16 ga. was placed on saw horses. If you do not give the 16 ga support (a flat surface to lay on. full contact) you are asking for "oil can" results. The welds will shrink the 16 ga somewhat (if you don't BURN it in) and should tighten the whole sheet. If you tacked all the way around the perimeter and then began your fill in, you are asking for an oil can result as the metal has nowhere else to go. But I digress.

    I am sure that what you show as "OUT" and "IN" will reverse itself with a bit of pressure. Other words, In will become the out etc. This is "oil can".

    First measure your box sides for square. Heat does funny things to angles. If square, then it is a matter of shrinking the panel.
    Get a OX/AC torch with the smallest tip you have. Get a bucket of cool water and a rag. Heat a dime sized area (in the very center of the concave) with the torch (flame should soft- the center of the flame 1/2 inch yellow and the tip of the blue about an inch to inch and a quarter long) You can adjust it (shorter yellow center/ shorter blue) if the time to bring the dime sized area to a bright yellow is longer than 5-7 seconds; you do not want the dime sized area to melt any material. Get the rag (wet of course) and apply same to the heated area. (Steam created will go through the rag quick, so watch your fingers!) Do not apply heavy pressure, just keep turning the wet rag until you don't hear the hissss. You will hear the metal contract. Sometimes one shot is all it takes. Then there is reality, and you have two smaller con-caves where on big one was before. Just go to the center of each one and repeat. I do not do the hammer first and wet last as some say to do, we do not build pianos and if you get it too hot you will have a very hard dimple to hammer out cold. Just remember, steel moves as it wants, we have to learn to patiently bend to its rules of movement. Take your time, do not rush. Observe, learn. I would heartily suggest you practice on scrap first to learn just what the metal is doing when you change the metal's environment with heat, cold, tools.
     
  20. metalfaber
    Joined: Feb 2, 2011
    Posts: 218

    metalfaber
    Member
    from Nebraska

    I disagree. if you weld around the outside, the outside edges will shrink. It will do the same thing as if you took the panel and used a shrinker/stretcher unit with shrinker dies in it around the entire perimeter of the panel. It will start to make a bowl in a sense because the outside is shrinking and the inside is not.
     
  21. john worden
    Joined: Nov 14, 2007
    Posts: 1,688

    john worden
    Member
    from iowa

    Good shrink technique here. I wish you would have used 18 guage with strength beads formed in it and cooled each short weld with compressed air as you progressed. Time consuming for sure. If DEAD FLAT panels are your goal you will know very soon into the straightening process whether or not this is a prototype. A bulls eye dent lifter will be of value but moving 16 Ga. won't be that easy. Luck. John
     
  22. 51 Henry J
    Joined: Nov 21, 2011
    Posts: 20

    51 Henry J
    Member

    Your statement is true. With one cravat, you, being a metal fabricator, would not allow heat to accumulate at the weld or throughout the panel with your welding. With the statements and picture provided, one can conclude inexperience has prevailed. Very few individuals will take the time to allow the heat to dissipate from the panel as a whole, let alone the weld site.

    It is at the point of the weld you have the greatest shrinking, the rest of the heat is pulled into the panel as the panel begins to act as a heat-sink. (one can see this even between too hot skip welds when the sheet has to be pounded back to flush before filling in between the welds. It is hot or many welds that heat gradually builds up and will expand the work but not shrink quickly or completely or evenly. This expansion however slight on a large panel will work against alignment for additional welds and if tacked all the way around, and the center is expanding from accumulated heat, it will oil can. Small areas will be less affected, but over a box side, much. Just putting down uneven length skip welds will cause distortion in a panel.

    Professionals and seasoned (school of many additional hours of shrinking mistakes) amateurs can tack perimeters and get by with it if they do not get the, " Damn, only 180 tack welds to go, I have to get this done now" thing going in their head.

    Short consistent bead length (low heat at the weld site) allowing heat to disperse (get off your arse and move to another location frequently), and feeling and watching what the metal is doing, is the key to large panel welding.

    Looking at the skip welds on the box side, I see short and long strings of weld, that means lots of inconsistent heat into the panel, a panel that is not supported adequately, and if it were, there still would be heavy shrink at the longer weld sites and expanded metal away from the weld site after the cooling.

    The hardest thing I had to learn welding body panels was to go slow, let it cool adequately and observe not just where I was working, but the affects occurring outside of my instant focus. Once I quit welding like everything was a 24" H-beam going into a bridge, my body panels suddenly straightened up, all by themselves, imagine that.
     
  23. 51 Henry J
    Joined: Nov 21, 2011
    Posts: 20

    51 Henry J
    Member

    Thanks John.

    The compressed air is also a very good shrinking tool and a lot less messy. I would like to see most projects in 18 gauge with a bead roller application, it makes life so much simpler...

    And I do hope this is not a "prototype", there is a whole bunch of material and time in this project. But tuition is steep in this art form.
     
  24. fleet-master
    Joined: Sep 29, 2010
    Posts: 1,774

    fleet-master
    Member

    here's how i did one recently. the sides had no swages or 'wheel' in them and i wanted to keep them lookin nice.
    I deleted the checked out area in the fender that allows for the original swages in the bed sides. The fenders bolted up real nice...but i had to take my time on it.

    sorry if i've uploaded the pics out of oredr :D:D
     

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  25. 51 Henry J
    Joined: Nov 21, 2011
    Posts: 20

    51 Henry J
    Member

    I just got goose-bumps. You sir are a true metal craftsman. Beautiful, beautiful art.

    Thank you.
     
  26. Jalopy Jim
    Joined: Aug 3, 2005
    Posts: 1,867

    Jalopy Jim
    Member

    I am learning a lot here maybe a little to late. One reason I picked a 53-56 F100 to learn on is they a easy to find parts for. Last night I did pull some of the crown out of the dents. One thing I am learning is to heat and cool spots about the size of a dime at the top of the crown, and then go to the next crown, ect. Excessive heat got me into this mess and I do not need to add to that. And looking back solid welding the edges was probable where the problem was created. But 5 years ago I had no experience doing metal work and the adventure of learning a new talent is a big reward. I am a professional furniture maker by trade and learning metal working is quite an adventure.
     
  27. john worden
    Joined: Nov 14, 2007
    Posts: 1,688

    john worden
    Member
    from iowa

    Understanding and mastering shrink and stretch in sheet metal is the key to nearly every sheet metal fab or repair job. Stay with it and you will be skilled in a second craft. I'll bet you plan to make a nice wood floor for that box. The attached photos show a replica box I built for a 42 Dodge WC. All new fab with a set of restored stake pockets and an original tailgate. Painted wood floor. Green over black Centari acrylic enamel, no rub or buff.
    john
     

    Attached Files:

  28. fleet-master
    Joined: Sep 29, 2010
    Posts: 1,774

    fleet-master
    Member

    re:my post above....I forgot to ad that the sides are made out of 20g zintec, the front bed wall is out 16g and the corner pockets are 16g also.The angle pieces plug welded to the sides are 18g.
    I added 1/8 plate corner gussets at the rear lower corners for bracing as when the t/gate is down they can tend to flop around a bit. With the fairly small triangular braces it was pretty good n solid.
     
  29. 51 Henry J
    Joined: Nov 21, 2011
    Posts: 20

    51 Henry J
    Member

    Jalopy Jim.

    You are a success in my book, you started and haven't stopped. You realized a problem and sought information. You are learning and applying that information. Good on ya'. That is how it is with us, that is why we belong to this site. Individually we will NEVER know it all, but between all of us on this site (ahem, and other similar sites), all is known.

    Keep us posted on the build.
     
  30. Jalopy Jim
    Joined: Aug 3, 2005
    Posts: 1,867

    Jalopy Jim
    Member

    I have about 1/2 the crown out of the three on the right side panel. It is working better now that I heat a smaller area at the highest point of the crown cool it to a touchable temp and then go to the next crown. I have ordered a shrinking disc to fine tune the little bumps when I get closer.
    I have not decided what to put on the bed floor, I have thought of Aluminum diamond plate but I'm not sure it would look early 1963-64 build. The other option is a stainless trim around the edges and a floating white oak T&G floor.

    and many thanks for the help and encouragement.

    Jim H
     

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