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Mig Vs Stck for project???????

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Mig Vs Stck for project???????

Postby thatoneguy » Fri Mar 03, 2017 8:52 am

Hi. So I'm gonna be building a giant cross for my church. When done its gonna be 12' tall made out of 8" square tubing 3/16" wall thickness. The tubing will be turned 45^ so that while facing it you are not looking at the flash surface but at and edge. The bottom vertical piece will be notched allowing the horizontal piece to be placed also at a 45^ angle into the notch and then the top vertical piece also notched will be placed on top. Now I have a 275amp MIG so I'm probably just going to end up MIG welding it entirely but just out of curiosity do any of you think it would be beneficial to stick weld this project? 3/16" wall thickness material is well within the capabilities of my MIG machine but I'm just curious if you think some stick welding would be the way to go? Or would spray transfer vs better than short circuit? Thanks!
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Re: Mig Vs Stck for project???????

Postby thatoneguy » Fri Mar 03, 2017 9:04 am

Or maybe even dual shield? I know I'm making a simple project complicated but I like to experiment to keep things interesting. I've never run spray arc on anything thinner than 3/8" and have never run dual shield at all. So what dual shield wire would you recommend to run with C25 gas???
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Re: Mig Vs Stck for project???????

Postby Oscar » Fri Mar 03, 2017 10:37 am

Why not complicate things even more? TIG the thing, but don't make it easy---use an exotic filler rod like Inconel or Hastelloy. You can never be too sure!! Oh, and make sure you get a good back-purge going. :lol:
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Re: Mig Vs Stck for project???????

Postby Olivero » Fri Mar 03, 2017 10:46 am

Oscar wrote:Why not complicate things even more? TIG the thing, but don't make it easy---use an exotic filler rod like Inconel or Hastelloy. You can never be too sure!! Oh, and make sure you get a good back-purge going. :lol:


Hahahaha!

No, gotta weld something like that in a room full of Argon and you bring the diving suit and oxygen tanks :lol:
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Re: Mig Vs Stck for project???????

Postby Farmwelding » Fri Mar 03, 2017 10:51 am

Well, if I was you I would run with something I have experience with. It isn't anything critical but you don't want any problems. If you want more practice on stick then you could run that to practice long runs and restarts. If you have a little while to build it then you could pick up a spool of dual shield wire (Lincoln is a good wire) and practice a bunch and then weld it up. Or you could do one part with stick, another with mig, and then another with dual shield and get a lot of practice with different processes. I don't know where you live so I can't say for weather conditions how structurally sound it has to be. If you have a lot of wind or live on the coast then go with whatever makes the strongest weld for you.
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Re: Mig Vs Stck for project???????

Postby noddybrian » Fri Mar 03, 2017 11:28 am

It worries me slightly the fact your asking this as it implies an experience level on the low side considering the weight & potential of injury should this thing fail in strong winds or such like - but despite some slightly off hand comments from our more jovial regulars if the church is happy for you to do this & they accept responsibility then lets try for some more helpful comments - Mig is fine if using sufficient power & a 275 on that material thickness is just fine - as to spray or short circuit that is very open ended as the wire thickness & gas mix has a great influence on the voltage this changes - if you can support the cross so all your welds are flat ( 1G ) then using spray is suitable - if you cannot & must weld to some degree in position especially when wrapping the corners then keep with short circuit - if you can get some similar scrap material to practice on maybe use the Miller welding website for baseline settings & just do some mock up joints & test them - if you can prep to allow a near full thickness V prep this is by far the best - if it's not possible then your question of Mig or Stick is valid as the next best option would likely be burn the hottest root pass you can with a cellulose rod as Mig is renowned for poor root penetration then grind back clean & fill with the Mig - do plenty of passes so there is adequate leg length to spread the load onto the limited wall thickness to reduce the chance of fatigue cracks - dual shield will work but is not generally used or recommended at this thickness - biggest question I'd have is not so much the cross part itself as how is this fixed down ? are you welding to a base plate or is it to be set in concrete in the ground - either way I think you need a signed waiver that you cannot be held responsible in the event of failure either now - next hurricane of 20 years time after no inspection / maintenance & the box rots off at the ground - these jobs while taken on with good intent can bite you - once a steel structure is in a public space / building it really needs to be drawn up by an engineer with - built to a spec & signed off by a qualified inspector due to our modern society - others may have different views & hopefully others will post with more direct advice on the pure welding aspects of your question - good luck however you proceed.
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Re: Mig Vs Stck for project???????

Postby Artie F. Emm » Fri Mar 03, 2017 11:32 am

First, good on ya for using your skills to make this for your church! I like the square tube turned 45* idea.

As to which process, either way you're going to want full penetration welds. It may turn out that the place you weld it in drives that decision: outside in the wind? Stick. Back at the shop in ideal conditions? MIG. But now may *not* be the time to experiment with a new process like dual shield: the final exam is not the time to learn the material.

Don't get me wrong, I'm totally with you: learning, experimenting, figuring it out is the fun and compelling part of any project. I get it! But as they say over on WW, the last thing you want to do is injure any nuns/widows/orphans/puppies because the welds on your cross failed.

That said, and with safety and longevity in mind, I don't think you can over-think this. I did some checking, and found that 8" square tube in 3/16 wall is 19.63 pounds per foot. If the vertical is 12 feet and the "arms" are 6 feet, your cross could weigh as much as 350 pounds. Where and how will this be mounted?

The way you design it can affect the overall weight and the amount of stress your welds endure. For instance, you might start with a 12 ft. vertical and weld the "arm" members to each side. Gravity will be pulling on those welds forever and ever amen, and those stresses will increase every time the kids from the youth group climb up on your cross. (Count on that, btw!) On the other hand, you might start with a 8 foot 4 inch vertical, and lay a single 6 foot horizontal member on top of that. That way gravity is pressing the horizontal down onto the upright, and your welds are holding it together rather than keeping it from falling apart. Finish with a 3 foot "INRI" top part of the cross. (And cap the exposed ends to prevent internal rust and bird nesting.)

How's that for preaching to the welders?! Sorry if you knew all that already. Good luck with your project, post up some pics!
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Re: Mig Vs Stck for project???????

Postby Farmwelding » Fri Mar 03, 2017 11:36 am

If it is an extremely critical job that is subject to strong winds and extreme weather at any time than whatever you know how to do and do well. If you can't do spray transfer and haven't done it then probably don't do it. As Brian said as well-ANYTHING YOU ARE TOLD TO DO OR ANYTHING YOU DO GET WRITTEN CONFIRMATION THAT IT IS OKAY. EVERYTHING HAS TO BE IN WRITING AND SIGNED. IF IT ISN'T IN WIRITNG YOU COULD GET SCREWED. MAKE IT AS STRONG AS POSSIBLE.
Sorry for yelling so much and so loudly but it is very important.
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Re: Mig Vs Stck for project???????

Postby Artie F. Emm » Fri Mar 03, 2017 11:37 am

Some responses popped up while I was typing. If I can suggest: read and re-read NoddyBrian's post! He makes a lot of good points.
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Re: Mig Vs Stck for project???????

Postby noddybrian » Fri Mar 03, 2017 11:49 am

Thanks - it's funny how often people post almost together & you go back to re-read to check how bad the spell check messed up & someone got the almost identical answer in before you !
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