[thatoneguy]

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!

[thatoneguy]

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???

[Oscar]

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.

[Olivero]

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.

Hahahaha!

No, gotta weld something like that in a room full of Argon and you bring the diving suit and oxygen tanks

[Farmwelding]

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.

[noddybrian]

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.

[Artie F. Emm]

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!

[Farmwelding]

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.

[Artie F. Emm]

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.

[noddybrian]

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 !

[Poland308]

Dito!
Mig or stick. Get a good solid weld. 3/16 is more than enough thickness for what your doing and thin enough that either stick or mig will get you full penetration.

[ryanjames170]

i will post this.. on top of what others have said..

if you do most all of your welding with MIG and do not do much stick welding.. MIG weld it..

If i was building something like that i would Stick weld it! why because i do more stick welding then MIG welding.. i can usaly run a few practice welds on scrap and get myself right where i need to be with stick but with MIG it takes me a good day to get the feel for it again.. i also know the settings faily well for my machine and know what it dose and dose not do well. and im sure you would feel the same about your MIG machine.. basically if you look at a stick welder and are not overly sure what amperage and rod you should be running with what your planning to do but have a prety good idea what your settings need to be on your MIG welder.. just MIG weld it.

how ever if stick welding interests you for future projects i would say start burning some rods and getting good at it.. as some have said sick welding has uses especially out door welding.. this is part of why they still stick weld on pipelines.. how ever flux core is another option how ever if you have not welded with it much i wouldn't use it.

[Otto Nobedder]

Amazing, isn't it, how slow this forum seems at times, and then three or four responses pop up on top of each other.

If this were my personal project, I'd stick weld it, bevels and open roots, 6010 and 7018. However, I have a load of experience with this. In the OP's position, he has the right equipment to MIG weld it, and do it well. I would suggest beveling the arms where they meet the upright, and holding a gap, for full penetration, but there's no reason a sound MIG weld won't do this job safely, pending the operator's ability.

Steve S

[homeboy]

As to the method of welding I am not proficient in the various methods described but with each connection having aprox. 3ft of weld any competant welder should be able able to glue this together. The weight itself is negligible but the issue is lateral loads "wind -vehicle strikes whatever" I totally agree with Noddybrian that the base and connection are critical. Cover your your butt -do any local building code regulations apply -signage-setbacks etc. I f so they may require engineered drawings and spec's . You can go for a tour and see how other similar free standing structures are anchored. In Ontario Canada we have a standard blanket building code but each municipality can have additional bylaws. When in construction I covered a lot of municipalities and it was a constant job to keep up with the rules. Good luck

[thatoneguy]

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!

As for the arms I was already planning on making the vertical piece the part that is split and just laying the horizontal into the vertical pieces's notch. And I will be capping the ends. Gonna be painting it with POR15 topcoat as well to prevent rust even more!

[thatoneguy]

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.

Ok read the original post again but with emphasis on CURIOUS. Lol. While this project does have structural critical aspects to it, the welds themselves are nothing crazy. I asked my questions because I am wanting to learn more of the in-depth metallurgical side of this. Tensile strengths, filler metals, etc... This is gonna sound somewhat arrogant, but I have more than enough experience and education for a project like this.

[thatoneguy]

And I guess I could have clarified a bit better on my original post... I have the stick and MIG experience to do either. And I have the equipment and machinery for welding and/or beveling if I decide to go that route. Along with the experience and education. My curiosity was more along the metallurgical side (for lack of a better way to describe it). I wanted to know more about tensile strengths, fillers, what kinds of what hold up better for stress flexing, weather, etc...

[thatoneguy]

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.

I actually have thought of using this opportunity to practice my Walking The Cup! I think I'm going to TIG weld the end caps.

[Farmwelding]

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.

I actually have thought of using this opportunity to practice my Walking The Cup! I think I'm going to TIG weld the end caps.

That's a good plan on the end caps. In bot a metallurgy expert or haven't had enough hood time and destructive time to make a solid opinion. Based on what I do know though, short circuit mig generally has less penetration and more issues like lack of fusion than most other processes. Sick provides good penetration along with spray transfer and flux core. But if you haven't run flux core don't do it in this.

[thatoneguy]

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.

I actually have thought of using this opportunity to practice my Walking The Cup! I think I'm going to TIG weld the end caps.

That's a good plan on the end caps. In bot a metallurgy expert or haven't had enough hood time and destructive time to make a solid opinion. Based on what I do know though, short circuit mig generally has less penetration and more issues like lack of fusion than most other processes. Sick provides good penetration along with spray transfer and flux core. But if you haven't run flux core don't do it in this.

Ya that is true. But their are ways to make sure that MIG does penetrate... Such as staying on the leading edge of the puddle, welding uphill, etc... I have experience with spray arc and gasless flux core but not dual shield. I don't know I think it is just going to boil down to whatever I feel like doing at the time.

[Artie F. Emm]

This is gonna sound somewhat arrogant, but I have more than enough experience and education for a project like this.

No offense intended. Everyone here wants only to help, but without knowing your specific qualifications, responses were offered with a fair dose of "please be safe" info. We've all cringed at those "I just bought a welder to build my airplane" or "what rod do I use to build a trailer" posts.

[Otto Nobedder]

From a metallurgy standpoint, E70s-6 Mig wire or ER7018 stick (or ER7014, for that matter) will give you both sufficient strength and sufficient ductility to withstand wind stress and it's own weight.

From a design standpoint, notching and welding on the bias is the best choice you could have made for ultimate strength. This significantly increases the length of weld, and puts the weld in favorable positions for the loads it will see. It virtually eliminates sharp corners, thus eliminating stress risers. It also eliminates welds that are perpendicular to the line of load.

I also think it will be more attractive as a finished product than simply square-butting it.

Steve S

[homeboy]

Question for Otto. In your comment you mentioned stress points at welded corners. The other day I was at the local fab shop discussing triangular gussets for a project and he mentioned it was stronger with the pointed tips nipped off. Is this a similar concept to spread out the stress at the ends of the gusset? Always looking to learn!!

[Poland308]

Not Otto but. Any time you can round a corner it will reduce stress. Often you will see patch plates with rounded corner, or when you weld windows into a boiler tube you round the corners of the patch to help relieve stress.

[homeboy]

Poland308--Thank you for the quick answer. Now I can see it makes sense.Just another detail to keep in mind to add to the data base.