what's the reason for spot welding or a continuous weld

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Hello all, I apologize if this sounds like a stupid question. was watching a youtube video of this guy building a truck bed. but it looks like all he did was spot weld the frame that the bed was going to sit on. what's the reason for this? wouldn't the welds be stronger if he ran a continuous bead? he was using square tubing for the frame. as always thanks.
Reply:Cost of application is the largest driver. Manufacturers strive to keep the costs as low as can be. Warpage, and secondary operations are another contibuting factor. In the private repair type application, we stive to produce the strongest yet most cost effective solution. We are not on the same time schedule as manufacturers to produce. Another reason is if the load concentration is not in an area that must have absolute strength, it is less expensive on all counts to use spot welding.Not a stupid question at all. Spot welding has it's place as do other forms.SlobPurveyor of intimate unparalleled knowledge of nothing about everything.Oh yeah, also an unabashed internet "Troll" too.....
Reply:We've seen some guys do a string of spot welds (tacks for lack of a better description) to get that stacked dime bead appearance thinking they're doing something cool and right when in fact they just lack the skill to lay a continuous bead with the "stacked" result.A look at the "MIG like TIG" thread has some examples of right and wrong ways to do it.http://weldingweb.com/vbb/showthread.php?30845-Mig-like-TigGot a link to that Youtube video so we can see what you're talking about?MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:Were these spot welds made with a spot welding machine or tack welds used to hold things in place until the assembly is done then a more substantial weld is made.  I see spot welds the same as using a fastener such as a #10 bolt or 1/4" bolt depending on the size of the spot weld and weld quality.  A line of spots welds can be pretty strong when used in the correct application.Dan D.Manipulator Of Metal
Reply:If you are talking about him using a MIG welder and making single welds that are about the size of a pea, it is because from the factory they used a spot welding machine or a pinch welder... You can get one from harbor freight, it's basically two long copper rods that can be "pinched" together at the tips; when you add some electricity you can easily weld two sheets of metal (at the pinch points) with no need for filler. Problem is, you need many sets of custom rods to reach all the areas of any given car/truck.If you use a MIG to spot weld and then grind/sand (i like to follow with a wire wheel to smooth it out) you end up with a welded spot that looks pretty darn close to what the factory would have done.  NOW, the reason i'm guessing the guy in the youtube video spot welded the frame of the truck before he put on the bed is because many people think (and i agree) that from the factory (some) car and truck frames were not welded to the best of the factories ability, i'm sure this is because time is money and it takes longer to do more welds. So, in turn, the companies did just enough to make the car safe and workable.Even FOMOCO published books that advised additional welding to be done on factory race-cars (BOSS mustangs come to mind). I'm guessing the guy in the video was trying to do the same.
Reply:Maybe I'm misunderstanding the question, but on automotive work one spot or tack welds a lot to avoid warpage of thinner steel like on body panels.  Then you try to connect the dots till it's full.  On a lot of commercial applications I've seen parts welded in small areas and that's it.  I think we get a bit obsessed at times with thinking that every part needs a full weld when a few small areas will do the job.  I'm not saying I have the experience to determine that.My '69 Vette has some of the cheesiest factory welds on the frame I've ever seen.  Many just little 1/2 welds.  No issues 40+ years later.
Reply:Take a 2 lb hammer and a 12 inch chisel and you'll quickly find out how strong a spot weld can be !Bubble gumTooth pixDuct tapeBlack glueGBMF hammerScrew gun --bad battery (see above)
Reply:i was surprised to see first hand how strong a series of small spot welds are. the 1/4" thick mounting brackets on our sliding cell doors are attached to the top formed sheet metal rail by 5 spot welds. occasionally they break from years of severe abuse like kicking,slamming and being pried open when they get stuck in the closed position but the majority are still holding.i.u.o.e. # 15queens, ny and sunny fla
Reply:thanks for the responses. just curious. from the video, it looks like the spot welds were pretty substantial. afterwards, he installed the bed which had closed compartments that he welded together. from the looks of those welds and his garage set up. he looks like an experience welder. not a newbie.
Reply:I have a spot welder we used in the shop for years putting 1/4's and uniside panels on cars, and bedsides on pickup trucks. It works very well and there is virtually zero cleanup after the process. Basically a d/a sander as with any sheet metal prior to under and top coats. Plug, and stitch welding in the same task is much more lengthy and time consuming. A 1/4 second 8000 amp instantaneous resistance spot weld is quite strong on automobile sheet metal. A chisel will split the surrounding metal prior to pulling the spot apart.SlobPurveyor of intimate unparalleled knowledge of nothing about everything.Oh yeah, also an unabashed internet "Troll" too.....