Needed: long seam clamp for sheet metal

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We're TIG welding 16ga stainless sheet that's rolled into tubes, approx. 33" long (maybe 1.5' in diameter).  So the seam that needs to be welded is about 33" long.The weld is a lap weld, on the overlapping part of the sheet metal after it's rolled.  There's about a quarter inch overlap.Depending on how [badly] it's rolled, the top part of the overlap doesn't always sit tight on the bottom.  And welding (no filler) 16ga stainless @ about 45-50A, you need a -very- tight seam, or that top layer just burns back on you.Right now we're using sheer physical force just by pushing down on the seam with a hammer and tacking it up, but often that's not enough to get it down tight (not to mention it's bloody exhausting when you have to do about 20 tacks along the seam first).  Long C-clamps only work so much, and only for the end parts.  If we make the c-clamps any longer they loose their pinching force the longer they are.Does anyone know of a type of clamp that can be laid down over the entire seam to basically crush the entire thing tight so it can be tacked up??I figure sheet metal TIG welders on here probably go through this sort of thing a lot, where a super tight seam is needed, but due to whatever distortions, can't be done without a very good clamp of some sort.  I just don't know what type of device I need.Anyone help would be much appreciated!!"A winner isn't someone who doesn't lose, a winner is someone who doesn't quit."
Reply:You can see a bit of the seam here and how it's overlapped. He's welding the seam. This particular part isn't too bad because it's just bare sheet metal with no other parts on it.  There's 2 other sheets with rings between them - they're the ones that tend to not overlap tightly, especially the outer (skin) sheet.Here you can see the inner drum, and the outer drum which is made up of 2 sheets with a ring spacer between them (all 3 sheets have a long seam that is fully welded (fusion TIG weld, no filler).  Seams not visible in photo (sorry) :There's a seam (not shown on this picture - it's on the bottom) that runs the length of the unit :Last edited by z0diac; 02-19-2013 at 08:14 PM."A winner isn't someone who doesn't lose, a winner is someone who doesn't quit."
Reply:So far, the only thing I can think of is making something myself, but I don't want to spend a lot of time doing it, as I've just been put on these parts and want to keep busy.I was thinking of getting 2 pieces of square tubing, something hefty like 1" square x 1/8" thick, welding on about 20 nuts to the top one, and using bolts to push down on the seam.  One square tube would run along the bottom, the other one (with the nuts/bolts) on the top.  (???)The other idea was the same but no nuts/bolts - having a steel caster on a track along the top, and the caster could be slide along the seam to pinch it tight for tacking.  All fine and dandy, but if there's a tool out there already for this, I'd rather just order it!!  "A winner isn't someone who doesn't lose, a winner is someone who doesn't quit."
Reply:In aircraft sheet metal work they use clamps called Cleco's. You insert them thru a hole drilled in both sheets and when you release them they act like temporary pop rivets to hold the pieces in place. You can use them anywhere in a sheet where you can get to one side and drill thru holes ( they also make edge clamps as well of the same design.Give me a minute and I'll add some links.Rog02 shows a good way to do an but joint with cleco's in this thread.http://weldingweb.com/vbb/showthread.php...ighlight=clecoI also know I've seen ZT use them in some of his ATV builds,  Here's one pict of one of his builds I used to show how to use Cleco's.http://weldingweb.com/showpost.php?p=410449&postcount=2Last edited by DSW; 02-19-2013 at 10:25 PM..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:I'd try just taking  a couple pieces of pipe bout 3' long, one inside and one outside with cant twist clamps forcing your laps togetherSafety 3rdGump
Reply:Long-reach clamps, like this (or similar):http://www.mcfeelys.com/product/CH-8...-C-Clamp-w-padNot quite enough reach?  Search for ones with a slightly longer reach or just take a pair (or a few pairs), cut the 'beam' part and weld in some steel 'extension' pieces to make an even longer-reach clamp.  You do have a welder, after all.  Another option would be the mentioned 'take a bar/beam/pipe on the inside and outside of the seam and clamp the two together and sandwich the seam between them.'  Add shims or spacers as needed to get clamping force/grip as desired.Take a chunk of pipe (3 ft long or a bit more) through the center of your workpiece to act as the clamping 'anvil', apply force/weight on top to push lap seam together and tack weld.  Also, have the roller 'guys' do a little better on the rolling.  Maybe have them come into the shop and see how if they are a little 'loose' on the diameter that you have some issues making the welds.  If they roll the metal a little 'tight' (but still to the desired final diameter), you can 'spread' the tube a bit and get the final desired diameter with the 'spread' keeping the seam ends tight(er) together than if you had to try and push those seams ends together.  The best laid schemes ... Gang oft agley ...
Reply:Expanding on Gump's suggestion, you might want to build squeeze bars. Like 1" x 2" bar for the inside that lays under the seam to displace air. And a 1" x 1" bar on the outside that allows room for your torch at the edge of the seam that will act as a gas dam as well. If they extend a couple of inches at each end, you could drill and put some 1/2 x 13 bolts to cinch the assembly tight.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:I like the idea of long bars that clamp the work together.   But I would note that if you want even pressure you may have to bow the bars slightly, to compensate for the flex in the bars.   Woodworkers do that when they want to clamp over a large distance, knowing that the piece of wood will bend.  I usually do a trial clamp, measure the gap in the center, and then put that much bow into the piece that I use for clamping. I believe that you could use a torch to put a little bow in the bars, by selective heating.I would probably make the upper bar with kind of teeth, with big enough gaps that I could tack weld between them.  I would assume that once it was tack welded every few inches, you would no longer need the clamps.The idea of a kind of carriage or roller that moves down the bars to do the clamping also sounds good.   That would  not be terribly complex to make.   A linear bearing could carry a metal wheel or roller that would do the actual clamping.  Look at the MSC catalog, part number 35528991. This is a pillow block style linear bearing.  I could imagine two parallel round bars, say three feet long, mounted horizontally on a support which is bolted to the floor.  You slip the rolled stainless on, perhaps using a band to keep it closed.  Then you slip on a connection or link between the two round bars at the free end, to stiffen it up.   At that point you start moving the carriage to the desired position.  There is no need for a carriage on the lower bar, just the upper.  You could even mount two carriages on the same bar to make it easier to clamp in a balanced manner.   I think that I could build something like that in an afternoon, once I had the parts in hand.     I would go for larger diameter bars for the stiffness, especially since they would not need to move.   This sounds pretty classy, and would adapt to a wide range of diameters.  If I wanted to make it especially elegant, I would include a leaf spring in the carriage to ensure constant pressure over the length of the bars.  You could use shims between the roller and the linear bearing to get the pressure about right.  I am not sure, but you might need Turned Ground and polished bars for the linear bearings to run on, but those are certainly available.A somewhat different approach would be to use bands around the diameter to pull the pieces together.  In this scenario, you would roll the steel a little larger in diameter than the final diameter, so that the bands pull it tight.  If one side came out higher than the other, then you might get into clamping, or else use thin prybars or thin pieces of metal to force the higher side under the lower side.You could perhaps use the same kind of bands that are often used for packaging, and then cut them and throw them away once they have served their purpose.   Those banders have provision for applying tension to the band, and then securing them with a crimping type connector, no need to invent anything, just buy a commercial product.Interesting problem.RichardLast edited by raferguson; 02-20-2013 at 05:11 PM.Sculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:Originally Posted by MoonRiseLong-reach clamps, like this (or similar):http://www.mcfeelys.com/product/CH-8...-C-Clamp-w-padNot quite enough reach?  Search for ones with a slightly longer reach or just take a pair (or a few pairs), cut the 'beam' part and weld in some steel 'extension' pieces to make an even longer-reach clamp.  You do have a welder, after all.  Another option would be the mentioned 'take a bar/beam/pipe on the inside and outside of the seam and clamp the two together and sandwich the seam between them.'  Add shims or spacers as needed to get clamping force/grip as desired.Take a chunk of pipe (3 ft long or a bit more) through the center of your workpiece to act as the clamping 'anvil', apply force/weight on top to push lap seam together and tack weld.  Also, have the roller 'guys' do a little better on the rolling.  Maybe have them come into the shop and see how if they are a little 'loose' on the diameter that you have some issues making the welds.  If they roll the metal a little 'tight' (but still to the desired final diameter), you can 'spread' the tube a bit and get the final desired diameter with the 'spread' keeping the seam ends tight(er) together than if you had to try and push those seams ends together.
Reply:Originally Posted by rafergusonI like the idea of long bars that clamp the work together.   But I would note that if you want even pressure you may have to bow the bars slightly, to compensate for the flex in the bars.
Reply:Originally Posted by z0diacGreat idea.  Just concerned that the bow would just bend straight and stay that way after a couple uses.  I might just try two long pieces of sq. tubing, with a 1" gap on the top one between the top sq.tube and the workpiece, so I can use that space to fit in a piece of strong flatbar or something to 'pry downward' on.
Reply:If you pick heavy enough material, and tie the free ends together, you will not have a problem with bending or taking the bow out of the horizontal bars.  If you don't tie the free ends together, you are very likely to bend the bars.  You literally quadruple the strength of the bars by tying the free ends together, I checked the formula.  Anything cantilevered is relatively weak.  Even if you given them an easy way to tie the ends together, the operator may be inclined to skip it, and then you may have a bent bar.  I would suggest that you might be better off with a largish diameter pipe for the lower bar, to provide a wide surface to work against.  Alternately, mount a piece of flat bar , maybe 1/8 or 1/4 inch thick, on the lower bar, and round it some with a grinder or with heat and a hammer.  I might go for heavy wall tubing for the lower bar, and then grind the top a little bit round.  Heavy wall tubing already has rounded corners.I had never seen the expando pliers, but that is a cool idea.  Maybe attach them to a kind of carriage, even if the carriage is as simple as a piece of square tubing.  Realize that the expando pliers might exert enough force to bend the bars.I could imagine using a wedge instead of a carriage to force the ends together.  You could make as many wedges as you desired, and use them in any combination, to get the desired result.I would consider offsetting the two bars a little, given the overlap on the material being welded, to improve access for the torch.  But perhaps that could cause its own problems.  Probably it would just be better to make the lower bar wide and the upper bar narrow.Note that the bars need to be far enough apart to get your torch in.   You should mock that up before you fabricate a massive fixture.  I would think 3 inches apart would let you get a TIG torch in, with the short back cap.   I have an ongoing requirement to get into a small space and TIG weld, so I bought a smaller torch than the WP17 that came with the welder.Good luck,RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:All great ideas guys!The one I'm going to use is a metal cable that runs the length of the seam, flatbar on both ends that will 'hook' around the ends.I'll slide on a piece of roundbar over the cable, and to the roundbar will be welded a piece of flatbar, with about 1" extending on the bottom (to pry the seam with) and 6" or so on the other end (to use as the handle). Kind of like an uneven teeter-totter.Simply clip the ends on, then slide the roundbar/flatbar down the seam and pry it down as I go.I'm not entirely sure it will work, as I don't know how much force will be exerted on the ends that it's hooked around - I don't want to be pulling the ends in and distorting it.  But the amount of downward pressure exerted by the pry will be divided between the two ends, so I don't thing it will really be an issue.I'll take a photo of it once it's made Last edited by z0diac; 02-24-2013 at 12:22 PM."A winner isn't someone who doesn't lose, a winner is someone who doesn't quit."