Basic channel to plate question

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I have to weld the ends of 3" x4.1# channel and W6 X 12# beam to 3/4 CRS mounting plates. I have a Millermatic 250 that I am guessing will be about at max. I also have a new Dynasty 350 DX that I could stick with. What are the pros and cons of either? And what type of stick to use also. I currently do not plan on grinding the millscale because there is a fair number of pieces to do.
Reply:So you plan to weld all around the beam and channel to the 3/4 CRS plate? One or 2 plates per channel and the same to the beam (each end?)? You haven't provided the configuration you are asking about.  But- W6x12 has a web of .23, and a flange of 1/4 nominal, if welding all around, then I think 3/16 fillet is plenty. Your C3x4.1 has a web of .17 nominal, I think also a 3/16 fillet all around should suffice. You should give your 3/4 CRS a minimal preheat at least. I would use a minimum E7018 or higher. I make no guarantee as to the accuracy of this information, as you have not provided any real design info to go on other than the power source you wish to use.
Reply:Typically for a fillet weld, you base the size of the fillet legs on the thickness of the thinner material, so I'd say 1/4" for the W6x12 and 3/16" for the C channel approximately.For stick, I'd probably run 1/8" 7018 at 125 amps or higher if welded flat. I might even opt for 5/16" 7018 with higher amps on the wideflange, to do everything in one pass if you can manage warpage doing it that way. 7024 would also be tempting to lay down a lot of material in a production setting if all the pieces can be welded flat and don't need to be done out of position. Down side of 7024 is that it's not used for much code work any longer, so if this is for structural use, I'd just opt for 7018 since many codes, like for structural work, often call for it.Solid wire mig, I'd run at least .035 wire and C25 gas and I would prefer to run the 92/8 argon co2 they use at the tech school with the XMT's if I had a power source that liked it. I'll leave suggestions on FC wire to the guys who run it more frequently, but I'd guess they would suggest .045 wire. I know not all FC wire is seismic rated and it sounds like you probably have an application where this might be where you want to run a seismic rated wire, if this is for structural use. Same goes with dualshield wire. I just don't use it, so I won't make any suggestions on that.I doubt 1/4" fillets would require you to max out the MM250. I wouldn't have any problems doing 1/4" code quality welds on my MM185, but duty cycle on my machine would be the big issue. The extra duty cycle on the MM250 should be able to take care of that.I'd opt for the process you do best. Mig would crank out the pieces the fastest in a shop and probably be the most efficient as far as consumables used. Stick would be my choice in the field, but then I can run either no problem.I do want to question if this is something you should be tackling. The questions you are asking are fairly basic. This sounds like structural members for something. Not a project I'd suggest someone who is asking basic questions should tackle. If you can't do basic code quality welds, and have the insurance to cover structural work, you might want to think at least twice about this..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:Thanks for the help. Pre heat? What temp? The W6 are 8' uprights for cantilever rack columns and the channel will be welded to 4x4 plates for the adjustable arms. I plan on a few practice pieces and if they pass the sledge hammer test I will continue. Bottom 2 arms will be 24" and the uppers will be 18" deep. This is for my own use and very overbuilt. All that is left before the sparks fly is a ton of .5 holes for the adjustable arms. 2.5" OC. The Mazak will make short work out of that.I guess I'll do MIG as the last time I tried stick was about half a century ago, and none of the welding is out of position. The 350 TIG is brand spanking new and not even hooked up yet.
Reply:Originally Posted by Sputter FizzleThanks for the help. Pre heat? What temp?
Reply:I haven't welded much cantilevered racking, but I've certainly assembled more than a bit of it when I used to do store remodels for one of the big lumber chains yards years ago. 3/4" plate for the ends is a bit on the heavy side. I'd want to say the plates on the arms weren't any heavier than 1/2" tops, 3/8" more likely, and that was using 4" wide flanges, not channel for the arms and with arms that were about 4' deep to hold full hacks of lumber and plywood. Also the arms were not 90deg cuts, but tilted up maybe 5 or 10 deg so if there was any sag, the material wouldn't want to move away from the verticals. Some of the verticals were even set back at an slight angle themselves. Base "arms" were usually at least the same materials the uprighhts were made of, in your case W6's. This increased the stability of the whole unit and gave you plenty of room to drill and anchor the legs. Keep in mind this stuff would support pallets and hacks of lumber, in some cases weighing in at more than 2 ton, some times as high as 16 to 20' in the air. ( pallet of roof shingles was just about 4000lbs and would sit on 2 or 3 arms depending on how they spaced the uprights.) I wouldn't suggest you working on something like that.However I've built a bunch of smaller cantilever brackets, mostly for holding form lumber and so on out of light weight materials for the concrete company I worked for later. I'd have no issues with someone welding those up even with minimal skills. The max loads are spread out over quite a few arms, so no single one is taking more than maybe 100 to 200 lbs tops. The steel would start to bend long before you'd fail even poor welds given the amount of surface area welded on them.Intended use and design would play a big part on whether I'd say someone is ready to do something like this, as well as welding skills. I'd really need more info to make the call. If I had to, I'd say this is more of an "intermediate" to "advanced" level project depending on it's use and design..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:Originally Posted by Sputter FizzleThanks for the help. Pre heat? What temp?