Newbie with project

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Hello,  I am new to welding ( i have my brother teaching me some basics and plan on taking some classes in the near future as well) but I had a question I have been unable to find an answer to probably because I don't know the proper terminology to search for.  I have a project I am working on which will involve welding at some point, whether I need lots of welding relies on hopefully an answer:I need to create a skeletal structure for a project I am working on.  There will be 2 outside supports and a few cross supports.  The outside supports I need have to have a particular shape (see attached, bottom drawing is the shape I need to obtain), basically a figure 8 (block type) and the sides open with a thin slit on each side.  The question is if I can't find that shape tubing, but could find half of it and just doubled and welded together back to back, will the welded structure provide the same support as a single piece?  My options are aluminum or steel.  This will be for outside use, and will probably need to support 500 lbs.  I don't know dimensions yet, just want to know can a well done weld of 2 pieces provide the same support as 1 single piece?  thank you.
Reply:The bottom is the shape I need, the top could be 2 pieces welded together to form the bottom shape, also anyone know if this shape has a name?Last edited by neildiamond11790; 04-16-2014 at 12:18 PM.
Reply:Unfortunately, I dont think you are going to find exactly what you need easily.  Unistrut is the closest think I know to the first shape.  It is not typically structural though.  Mostly used for pipe supports etc.  2 pieces could possibly hold 500 lbs.  As for taking a piece of square and cutting out your channel, you will get a lot of warping as soon as you cut.  you can cut slots but fully cutting one side will cause it to open up wide or close down depending on the stresses present in the material.  Another option may be to use 2 pieces of U channel and a flat plate.  In your second pic, take the top and bottom as U channel and then a flat plate to connect them.  Welding will cause some bowing but control your heat and it shouldnt be unbearable.Aluminum is much harder to weld than steel.Multimatic 200Ellis 1800Haberle S225 9" cold sawMM 300;  Spoolmate 30A w/ WC-24TB 302GDynasty 280 DX Tigrunner
Reply:Originally Posted by DrooopyUnfortunately, I dont think you are going to find exactly what you need easily.  Unistrut is the closest think I know to the first shape.  It is not typically structural though.  Mostly used for pipe supports etc.  2 pieces could possibly hold 500 lbs.  As for taking a piece of square and cutting out your channel, you will get a lot of warping as soon as you cut.  you can cut slots but fully cutting one side will cause it to open up wide or close down depending on the stresses present in the material.  Another option may be to use 2 pieces of U channel and a flat plate.  In your second pic, take the top and bottom as U channel and then a flat plate to connect them.  Welding will cause some bowing but control your heat and it shouldnt be unbearable.Aluminum is much harder to weld than steel.
Reply:Unistrut is going to be the easiest way to go and it will hold a lot of weight. I have saw horses I built from it and they hold lots of weight without flexing.GravelThe difference between theory and practice is that in theory there is no difference.
Reply:Could you use 2 pieces of unistrut back to back with a square or rectangle tube as a spacer?Miller xmt304,  Miller S22 p12, Miier Maxstar SD, Miller 252 w 30A, Miller super32p12, Lincoln Ranger 9, Thermal Arc 181I with spoolgun, Hypertherm 10000 ,Smith torches. Esab 161lts miniarc.
Reply:Unistrut actually does make a back to back piece just like the second picture that you have. It comes from the factory like that. I don't know the exact name of it,  we always call it double strut. Pipe fitters and HVAC guys use it to hang their bigger fixtures. If you can get a hold of someone in the commercial or industrial construction business or find a grainger company near you. we have left over strut all the time and I can usually get all I want before it goes into the trash. Good luckLast edited by vettersjake; 04-16-2014 at 09:03 PM.Reason: MispellPrecision tig 225Millermatic 185 w/ spoolgunLincoln 140Dewalt cold saw
Reply:Originally Posted by vettersjakeUnistrut actually does make a back to back piece just like the second picture that you have. It comes from the factory like that. I don't know the exact name of it,  we always call it double strut. Pipe fitters and HVAC guys use it to hang their bigger fixtures. If you can get a hold of someone in the commercial or industrial construction business or find a grainger company near you. we have left over strut all the time and I can usually get all I want before it goes into the trash. Good luck
Reply:Originally Posted by EcondronIt's literally called "Back-to-Back". http://www.fastenal.com/web/products...endingMachine=
Reply:You can buy single unistrut at the big box stores.GravelThe difference between theory and practice is that in theory there is no difference.