Need help building this device

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I need something to support this type of structure.It will be the base of the 4x4 posts. I can not mount the base directly to the ground. It has to be temporary and easily moved. I was thinking about something like this as the base.The only difference would it would be fully enclosed and not just three sides. I would then add sand bags on top of the base to help support the structure. I'm thinking about using a 15" or 18" base. I could also buy some of the following supports and just weld a piece of metal to the bottom. I will probably just pay a professional welder to do it, but I was looking for some suggestions on what to do or ask for.What type of metal base and gauge should I use? Any suggestions are more than welcome.  I would appreciate any help.Thanks
Reply:What are the height and width dimensions and how much weight are you holding up?   You may not need any base plates if it's not too tall/skinny and/or not much weight is involved.  Many tables just have legs that end at the ground without a plate.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:It will probably be 8x8x8 feet. There is no top to the structure. It will just have trim boards (1x6) running around the top. Since it is an outdoor structure, I need the base plates just in case it gets too windy.
Reply:I would be more concerned with tying the legs together at the bottom than with putting feet on it.  4 legs sticking down that long without being anchored to the ground could flex/sway/wobble without being tied together around the perimeter, or cross braced together, near the bottom.   If it's going on a hard surface, feet shouldn't be necessary.  If its going on dirt/mud/grass/etc, then 12x12x1/2 plate feet would be good.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:If you are on dirt.  I would probably use some screw-in ground anchors to hold this down against wind.  Have a bracket with a hole welded up about a foot so you can install a turnbuckle between this bracket and the ground anchor.  DesertRider, ground anchors will also help the problem of unbraced legs.  If you're holding no more load than 10 or 20lbs you may not need 4x4 tubing or you can use very thin wall 4x4 tubing if you want the bulky look of the 4x4.  How thin can you get 4x4? 14ga, 16ga?  I only buy it in 1/4".  Heavy to move and way overkill for a 20lbs load.Dynasty200DX w/coolmate1MM210MM VintageESAB miniarc161ltsLincoln AC225Victor O/A, Smith AW1ACutmaster 81IR 2475N7.5FPRage3Jancy USA1019" SBAEAD-200LE
Reply:Do you live in tornado alley? IMHO you'd need a hell of a wind if you made that out of anything over 3/16 wall thickness. If your on soft ground, some concrete pier blocks or patio stones might do the trick. Like Desertrider and Andy said, need to keep the bottoms from splaying. If on soft ground, L-brackets or slices of angle iron flush with the bottom, with a hole in the bottom leg to drive a stake it. Drive the stake at a bit of an angle and you'll kill two birds with one stone as Andy said. Make the stakes yer self.Is that top curved sheet, textile material? Like a shade? Is that what this thing is?200amp Air Liquide MIG, Hypertherm Plasma, Harris torches, Optrel helmet, Makita angle grinders, Pre-China Delta chop saw and belt sander, Miller leathers, shop made jigs etc, North- welders backpack.
Reply:is that a choopah?
Reply:Can you put some Dimensions and materials on the drawing?  So we do not have to guess. Also how you are going to use it.
Reply:I haven't determined the final dimensions yet. Yes, it is a wedding canopy. I will not use the material in the center. It is probably just fabric. How much would a 12x12x1/2 plate weigh with 4x4 tubing? I would put two sandbags on either side to keep the base from moving. I will also use anchors if the surface allows for it. Thanks for all the suggestions.
Reply:1/2" plate is way overkill.  I would probably use 1/4" plate on the foot pads.  I don't know if you can drop down to 1/8" and still be stiff enough.My local steel yard shows to have 4x4x14ga tubing.  This is the thinnest they carry.  It is 4.32 lbs/ft.  So... 8x8 square top uses 32ft and 4 legs at 8ft uses another 32ft.  You're looking at 64x4.32 = 276lbs for this structure.  I would consider having bolt together joints on this thing.  276lbs isn't going to be easy to carry.  8x8x8 isn't going to be easy to load on the truck/trailer.  Individual 8' pieces would be much easier to load on the truck and carry across the yard.  You might even have it made like some of the warehouse racks where it just slips together with slots and tabs (a lot more design work here though).  For single use you could have it built on site, and then torch cut apart afterwards.Dynasty200DX w/coolmate1MM210MM VintageESAB miniarc161ltsLincoln AC225Victor O/A, Smith AW1ACutmaster 81IR 2475N7.5FPRage3Jancy USA1019" SBAEAD-200LE
Reply:Yeah for a wedding canopy 12x12x1/2" plate is a bit much.  I had no idea how he was going to use it though and normally if you're using a 4x4 tube to hold something up, it's something substantial and a 1/2" thick plate is appropriate.A portable wedding canopy, I'd build the frame from 1-1/2 16 gauge tube not big 4x4's...MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Not for strength but just for deadweight the 12 x 12 x 1/2 steel foot plates wouldn't be 'bad'.I read what the OP said about dimensions and usage and I hear him/her saying that the upright posts are 4x4 wooden posts 8 ft tall.  The entire structure is the base plates, then the 4 upright wooden posts, and then the 4 1x6 wooden trim boards connecting the tops of the upright posts together.Using some heavy plate as the base plates IMHO will look cleaner and neater than plopping sandbags or other weighty items around the bottom of the uprights.Also, the large heavy base plates will help minimize the drunk-guest-pushes-a-post-over factor.More than one way to build your desired item.  Like usual, it comes down to what and where trade-offs are made.Heavy baseplates versus adding sandbags, wooden 4x4 posts versus metal posts, etc, etc.And it doesn't take all that much of a breeze on a tent/awning/canopy to make things try and lift off.  So weight and anchoring it to the ground are GoodThings.  The best laid schemes ... Gang oft agley ...
Reply:Sorry about the confusion. The structure will actually be made out of wood. The only thing that will be metal is the base plate. The 4x4 tubing will act as a sleeve for the bottom of the posts. It will only go up about 6 to 8 inches. I would then bolt the sleeve to the wood post. I'm not even sure what the actual inside dimensions are for 4x4 tubing. I would prefer for the base plate to be heavy. I actually considered using a 35 or 45 lb olympic weight. The kind used for weightlifting. I was going to have the tubing welded to that, but I have read that it is difficult to weld cast iron. I'm assuming that is what the metal weight is made from. Can someone give me an estimate on how much a 12"x12"X1/2" base plate with only 8" of tubing welded to it would weigh? Thanks for all the help. I've seen some other people use just a concrete patio block (18"x18") and bolt it to the post.
Reply:I'm with Dessertrider on this one. But if the big chunky look is what you want, then go with thin wall tube. Even if the bride and groom are standing on top of it, not under it! So is this a one time usage? If so, like someone else said, bolt together, for sure. Easy transport and easy to reuse the tube for later project. One of your kids getting hitched?200amp Air Liquide MIG, Hypertherm Plasma, Harris torches, Optrel helmet, Makita angle grinders, Pre-China Delta chop saw and belt sander, Miller leathers, shop made jigs etc, North- welders backpack.
Reply:A wood 4x4 is about 3-1/2 x 3-1/2.  A 4x4x1/4 tube is about 3-1/2 x 3-1/2 inside, with rounded off corners.  The 4x4 wood should fit inside the 4x4 tube if you trim down the corners of the wood a bit.If you're depending on weight and area of footing to hold it down, weld the 4x4 tube to a 1/4" plate, bolted to a big rig truck brake drum...MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:nolo,A piece of steel 12" x 12" x 1/2" only weighs 20.4 pounds.  I don't think that would be too heavy at all.  If you make the sleeves/sockets for the wooden posts to slip into out of 4x4 steel 1/4 inch wall tubing and 6 inches tall, then that adds 6.4 pounds per base plate.  Total for each base plate is then about 27 pounds.  Each wood 4x4 8ft post will weigh more than that.Again, the thick steel base plate is not so much for strength but for anchoring weight and stability.  Hmmm, just for stability on the ground and some extra weight down low I might up the base plates to 16 or 18 inches square (46 pounds for 18x18 1/2 inch thick steel. plus the 6 pounds for the 4x4 6 inch tall 1/4 inch wall tube steel sockets makes 52 pounds per baseplate), still 1/2 inch thick.  Balancing an 8 ft tall 4x4 wooden post straight up with just deadweight is not so simple.I still think the thick steel (and 1/2 inch steel for this application is pretty thick and not really needed for the strength but more for the weight) will look 'cleaner' and less obtrusive than piling some sandbags around each post.  But hey, make the baseplates out of 1/4 inch thick steel and pile 4 sandbags around each post and they really shouldn't go anywhere then!  Also for planning purposes, note that a wooden 4x4 post is actually 3.5 inches x 3.5 inches as stated above.  Also you probably would not want the 'common' pressure treated 4x4 posts, but more likely something a bit 'nicer' like some kiln dried redwood or cedar or pine 4x4 posts.  Those would be smoother (should be any way) and would actually be dry as opposed to soggy wet PT posts.    You may have to look a bit for the kiln dried posts depending on where you are and what the lumber yards have in stock.  Not a big deal, just something to keep in mind is all.Also keep in mind that when you or whoever puts this thing all together to make the posts be plumb (straight up-n-down) to keep it all nice-nice and not look like some haphazard crooked house-of-cards.  That may entail some fiddling with the baseplates to get them level and even at the same height/elevation as well.  Depending on what you are planning on plopping this whole thing down on, a few bags of plain dry builders/sandbox sand could be used underneath the baseplates to help you level and even things out.Please follow up and let us know how it all turns out.  Pics of the thing might be nice too, we like  pics.    The best laid schemes ... Gang oft agley ...