Looking for a MIG...

Which Millermatic should I be looking for (probably used) and what would be a good price for a unit in decent shape? I will be looking to use it
(presumably with flux core) to assemble some rebar assemblies (5/8 rebar for grade beams), and for general purpose projects generally under 3/8" thick. TIG with my Syncrowave will still be my preference for most shop based projects.
Thanks,
    Pete C.
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On 8/2/2011 9:02 AM, Pete C. wrote:

For rebar work I'd just use your existing Tig and stick rods. Slag is not an issue so just fire up some 1/8" 6011 and be done.
Be VERY CAREFUL welding rebar. Most rebar is either C40 or C60 for 40KPSI or 60KPSI. But it also means that the easiest (cheapest) way to get those numbers is to bump the carbon to either .4% or .6%. This much carbon will give you an EXTREMELY brittle HAZ if the metal cools quickly (like it will with small joints!) These joints have no fracture resistance.
There is some weldable rebar out on the market but it is much more money than the regular stuff. It will be marked on the ends if it is. But don't expect to find this unless you both ask and pay dearly.
I have done a demo on the rebar: cut a couple pieces a foot long, lay a big soupy weld across them for 3 inches or so. Flip over immediately and lay a second weld on the back side. IMMEDIATELY toss into a bucket of water. Don the safety glasses and hit it with a sledge, it should shatter. I did it once where it would shatter when you dropped it from shoulder height.
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RoyJ wrote:

I suppose, but I'm not particularly good at stick and I figured MIG/fluxcore would be easier and faster.

I'm not sure how quickly anything will cool if it ends up being done in the 108F weather we are having here at the moment.

The key thing here is that the weld only serve to hold the rebar assembly in proper alignment while being moved into place and while the cement is being poured. After the cement is set the weld serve no structural purpose.
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Gunner Asch wrote:

Which works fine for keeping rebar in position when it's assembled in place, but fails miserably for a rebar assembly that will be jig assembled and them moved into place with a crane or forklift.
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Gunner Asch wrote:

I'm know how to tie rebar, I've done it many times. Nobody ties rebar assemblies that need to be craned / forklifted into place, they weld them. The assembly I will be doing will be about 25' square x 3' high and placed with a telehandler forklift. Wire ties aint' going to cut it.
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Welding with E6013 is very easy.

That's totally ok.
I welded rebar for the base of my mailbox. It has not shattered yet.
Same for the base for my grill.
i
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O

But I see a lot of tandom axle trailers that have the upper tie bar made from rebar. Welded to the frame on each end, several spacers along the middle to give decent triangulation. Good design, terrible choice of materials.
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Smirk. Just hook it up and buzz it. :) actually, you might find the longer cables and no bending restrictions on the cables to be a huge advantage over the 10' MIG stinger cable. A lot of guys will do this kind of weld by feel: just jab the rod into the gap, pull it along.

Ambient doesn't make a lot of difference as long as the numbers are positive.

Well, OK. But sometime next week/month/year you might get a batch of really high carbon rebar in. It meets spec for rebar but will give you a lot of troubles when you weld it. Also: the welded section should not be considered to be full strength so if the welded bar is a critical element, try to move the weld to a different spot.
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RoyJ wrote:

Well, over the limited number of 6013 welds I made in the field a few weeks ago, I was getting better at it. The arc control function of the Syncrowave seems to be a big help in avoiding sticking.

Up to 109F now *sizzle*.

Looking at a lot of highway construction around here, I see that the basic roadway rebar is tied since it is assembled in place. All of the other rebar for overpass support columns and their cross beams is welded in an assembly fixture on the ground and then placed with a crane. What I'm doing is large grade beams, so it's not quite as critical as an elevated beam supporting an overpass.
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On 8/2/2011 4:55 PM, Pete C. wrote:

Oh quit complaining. We are getting 80+ degree dewpoints. As soon as you move you sweat. But it doesn't evaporate so all you do is get wet and not cool. I'm not ready for that. I dropped 3 pounds in 3 hours and that was with what I thought was enough water. Sheesh. I'm too old for this stuff.
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Would 7016/7018 - the Basic (limestone) based rods help here? They are moderate-penetrating and stored correctly (but only if stored correctly - opinion is they reach about the hydrogen level of 6013's otherwise), they give low hydrogen. I'd have thought a small rod-oven is a lot lighter than carrying a MIG-set and bottle and a tent so the gas-shield isn't blown-away.
My impression is that hydrogen is a superstition rather than a rational reason when fab'ing truly soft structural steels like out "S275" - 275MPa or 40ksi - and especially in thickesses like 12mm not 120mm! Whereas in this case of carbons in seriously high range of 0.4% to 0.6% maybe would give bit of relief to be low hydrogen ???
Anyone comment on my logic here? What is the word coming from extensive experience?
Rich S
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Gunner Asch wrote:

Except that rebar welds serve no structural purpose once the cement is set, this is why wire ties are often used to hold rebar in position in settings where it is assembled in place. For more complex rebar arrangements they are usually jig assembled, welded and then moved with a crane, forklift, etc. and the weld provide the rigidity to keep everything together during the movement.
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I would have used stick E6013 rods for rebar. (there are various warnings that rebar should not be welded)
That said, I would say Millermatic 250, 251, and 252 would work great.
i
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Ignoramus2407 wrote:

I figured one of the 25x Millermatics, but I recall that there was some preference on the models. Something where one had more features, but another performed better. Perhaps Ernie will enlighten us.
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