Arc or Mig?

[CEJM]

We are building an agricultural steel framed building.(animal shelter) Due to planning issues the height of the building needs to be reduced by 2 feet. The easiest way to achieve this is by cutting 2 feet off the uprights. The uprights are 178 x 102 x 19 UB with a 8mm thick 300 x 200 plate welded to the bottom.
The uprights will be bolted to 400mm of concrete before being encased in another 700mm of concrete.

I now need to cut 2 feet off the stanchions before welding the bolting plate back onto them. What would be the best process to achieve this. Arc or Mig? The work will be done in the workshop so shielding gas blowing away is not an issue.

I own a Esab Rogue ES 180i arc welder and an Oxford Migmaker 301. However, I have not really welded anything over 5mm thickness.

The bolt plates on the stanchions are not structural as they will be encased in concrete, but I would still like to do it properly. Had they not been encased in concrete then I would have paid a coded welder to weld it all together.

What would be the better process to achieve the best result?

Many thanks.

 

[gaz1]

it would be arc using multipass for me

what height are we talking about ?

if your encasing in concrete what is your leg base going to be ?

personally i prefer bolt pads which means a thicker base plate which means the base pads can be cemented and setting while the foot plates are welded up

 

[zzr1200]

Depending on the power supply for the mig (if you have a 32amp supply), and can handle rolling the steels over for horizontal weld joint position, clean/grind the weld areas and spray weld the joint either a 1 or 3 pass weld (200/+ amp). Would be my preferred way.

Get a few bits of scrap and practice a few welds first.

I do enjoy stick welding for site, but in a workshop mig rules.

 

[knighty]

Mig it for ease

The feet are only to spread the load, it's all downwards force

By the time there's any other kind of load on the welds... the welds are the last are the last of your problems

 

[zzr1200]

From this sites, mig setting advice page, for your mig's amperage range.

So I'd go with setting, Course3 Fine 4 or Course 4 Fine 1 or 2, to start with, it could be dip or edging into spray transfer depending on your welders output voltage (25/27 volts min). be prepared the crank up the wire feed speed if it goes into spray. The arc sound changes from frying bacon (dip) into a hiss (for spray).

Estimated thickness for each power setting​

The table estimates the range of steel that might comfortably be welded for each power setting.

Power setting	Steel thickness (millimetres)
1​	0.8 to 1.0​
2​	1.0 to 1.2​
3​	1.2 to 1.5​
4​	1.5 to 1.9​
5​	1.9 to 2.4​
6​	2.4 to 3.0​
7​	2.9 to 3.6​
8​	3.4 to 4.3​
9​	4.1 to 5.1​
10​	4.8 to 5.9​
11​	5.5 to 6.9​
12​	6.3 to 7.9​
13​	7.2 to 9.0​
14​	8.1 to 10.2​
15​	9.1 to 11.4​
16​	10.2 to 12.7​

Notes about the estimates​

• 
  200) { echo ("
• This calculator may be inaccurate at thicknesses above 5mm
  "); } if ($min < 20) { echo ("
• The minimum current you entered might be inaccurate. Normally the minimum for a hobby MIG welder is about 30 amps.
  "); } ?>
• The estimates assume butt welding two pieces of sheet together, having penetration all the way through the sheet, and continuous welding.
• Speed of welding and differences in technique will affect choice of power setting. My own torch travel speed is relatively low (hobby welder speed). Power can be increased if the speed of torch travel is increased.
• Thickness estimates could be increased by about 50% if the steel were prepared with V edges.
• Thinner metal can be welded using an on/off stitching technique.

 

[Erie Fred]

You don't have uplift from wind loads ?
Post a pic of the foot as it is now, before you cut it.

 

[Porkypine]

For the job you describe I'd use Arc every time, no question.

 

[frank horton]

asnything thicker than 2mm gets arc at my place.....I do have a 180mig tho...

 

[Bornfree]

You have a 300amp mig. Perfect for the job.

 

[wyn]

I'd just cut the top off and drill new holes to bolt the rafter thingys to. (If that's how they are made)

Or dig the holes deeper.

 

[fizzy]

300amp Mig can easily do 10mm.

 

[tom2207]

what ever you fancy , it wont matter once its in concrete ,, thats a vert thick base at the end of it though , for whats relatively small uprights .

 

[Barking Mat]

Outside ? Not mig, arc everytime.

 

[CEJM]

Thank you everybody for your replies. Much appreciated.

The welding will be done inside and the stanchions are only 3.2 metres long. At 19 kilos a metre they are easy to handle. I have a 32 amp supply for the welder so can use it to its full potential.

The current plate is 300 x 200 x 8 with 4 bolt holes. The reason for cutting the bottom of the stanchions instead of the tops is so that I can do it myself. I wouldn’t trust my own welding enough for the tops. It has a plate with bolt holes on the top. The bottom plates are not so critical as they are bolted to 400mm of concrete and then encased in another 700mm concrete. In total each leg will have 1.1m3 of concrete around them.

 

[premmington]

Outside ? Not mig, arc everytime.

I too MMA weld everything of certain thickness outside...

 

[addjunkie]

Thank you everybody for your replies. Much appreciated.

The welding will be done inside and the stanchions are only 3.2 metres long. At 19 kilos a metre they are easy to handle. I have a 32 amp supply for the welder so can use it to its full potential.

The current plate is 300 x 200 x 8 with 4 bolt holes. The reason for cutting the bottom of the stanchions instead of the tops is so that I can do it myself. I wouldn’t trust my own welding enough for the tops. It has a plate with bolt holes on the top. The bottom plates are not so critical as they are bolted to 400mm of concrete and then encased in another 700mm concrete. In total each leg will have 1.1m3 of concrete around them.

If the bolts in cones are preset in the concrete, you will need to get all the feet on in exactly the right orientation on each upright, or laying out will be a pain.
Id mig it too, as its quicker, but a stick would work just as well.

 

[premmington]

If the bolts in cones are preset in the concrete, you will need to get all the feet on in exactly the right orientation on each upright, or laying out will be a pain.
Id mig it too, as its quicker, but a stick would work just as well.

Seven years ago ish - I put a new concrete ramp into a workshop door - longer lower approach for lowered cars.

Made a nice job of it - bull nosed front edge. I put some metal matting in it - few bits of rebar to make a cage in it.

I tacked rebar together with a MMA welder.

Every builder customer who came to my workshop - gave me the thumbs down for welding/tacking the rebar together.

Ramp not cracked with some heavy traffic over it - loaded 3.5ton vans/forklift. All thou I always over spec - make all my little civil engineerint projects too big/heavy (like castle building).


Always wondered why tacking rebar together was such a no/no....?

 

[Dcal]

Rebar can be and is routine welded in construction, in fact it's the standard way of joining some long rebar cages now, for example CFA cages.
The change to welding came about after a few nasty incidents where cages fell apart causing serious injuries and some fatalities.

The weld procedures used will be tested, qualified and certified but it's no big deal as long as the material spec is known and doesn't change.

Rebar has a higher carbon content than mild steel and a bit of care is needed, it doesn't like cold short tacks which can create hard spots which can crack and break, but mig and stick processes are routinely used.

But (there always a but) the reason builders think it can't be welded is because designers and specifiers don't like it (it's another unknown) but mainly because a few years ago the market was flooded with cheap Chinese rebar that was alloyed with Boron which cause the same issues with Boron in car structures and weldability.

Steel producers warn on Chinese rebar

Contractors are being warned that the use of Chinese reinforcing steel could be unsafe unless welders are specially trained in the specific techniques that it requires.

www.theconstructionindex.co.uk

 

[fizzy]

Seven years ago ish - I put a new concrete ramp into a workshop door - longer lower approach for lowered cars.

Made a nice job of it - bull nosed front edge. I put some metal matting in it - few bits of rebar to make a cage in it.

I tacked rebar together with a MMA welder.

Every builder customer who came to my workshop - gave me the thumbs down for welding/tacking the rebar together.

Ramp not cracked with some heavy traffic over it - loaded 3.5ton vans/forklift. All thou I always over spec - make all my little civil engineerint projects too big/heavy (like castle building).


Always wondered why tacking rebar together was such a no/no....?

Colin Furze does it on his tunnel and bunker build.

 

[premmington]

Rebar can be and is routine welded in construction, in fact it's the standard way of joining some long rebar cages now, for example CFA cages.
The change to welding came about after a few nasty incidents where cages fell apart causing serious injuries and some fatalities.

The weld procedures used will be tested, qualified and certified but it's no big deal as long as the material spec is known and doesn't change.

Rebar has a higher carbon content than mild steel and a bit of care is needed, it doesn't like cold short tacks which can create hard spots which can crack and break, but mig and stick processes are routinely used.

But (there always a but) the reason builders think it can't be welded is because designers and specifiers don't like it (it's another unknown) but mainly because a few years ago the market was flooded with cheap Chinese rebar that was alloyed with Boron which cause the same issues with Boron in car structures and weldability.

Steel producers warn on Chinese rebar

Contractors are being warned that the use of Chinese reinforcing steel could be unsafe unless welders are specially trained in the specific techniques that it requires.

www.theconstructionindex.co.uk

I welded it with 6013's - as I managed to beg/borrow enough mat and rebar for the job - plus I did not have any tying wire