[Spridgets] mig welder

[Bud Osbourne]

Just had to chime in, here, since part of my day job qualifications includes 
a very good working knowledge of welding, to be utilized in examining and 
approving/rejecting welds on large sheet metal structures (river towboats 
and barges).  I've also been welding, on a wide variety of stuff, for around 
45 years.
In this thread (which I, truthfully, have only been occasionally reading), I 
have detected some possibly flawed reasoning concerning duty cycles & sheet 
metal welding.  In short, if you are working on autobody steel and running a 
pass long enough to run up against the duty cycle "limit" of any welding 
machine; you are doing something horribly wrong.  Let me tell you about some 
welding errors I have observed, by non-professional or non-professionally 
trained welders (including a whole lot of guys who work in autobody shops):
First of all, there seems to be a mindset that "the prize" goes to the guy 
who can run the longest welding pass without blowing through the sheet.  In 
order to do this, they turn the voltage down to avoid (as much as possible) 
the heat build-up that is part of what happens when you weld.  The results 
are shallow penetration, an excessive, ropey-looking weld "bead" sitting on 
top of the joint (which has to be ground off, creating yet more sheet metal 
warping heat), more than a little bit of panel warpage and a weak weld.
To produce a good, strong, flat butt joint on 18 or 20 ga. sheet steel, you 
should only be running passes of about 1/4" at a time (after first tack 
welding every inch or so along the length of the butt, then grinding/filing 
the tacks flush), and immediately cooling the welds with compressed air. 
Take your time and skip around on the length of the butt, to ensure an even, 
flush joint.  If you do it right, you will be able to clean up the butt with 
a body file and use only a very small amount of filler to cover the seam.. 
Also, when you look at the back side of the weld, you will not be able to 
see the edges of the metal you've joined because they will be part of the 
weld seam.
So, in answer to what kind of MIG welder is best: Whichever one your 
friendly, local welding supply outlet recommends for you, after discussing 
your welding needs & abilities with him.  It's important to have a machine 
for which you can get parts and service for, locally.   One thing you MUST 
have is "infinitely variable" voltage and wire feed controls (basically, 
rheostats) because you will need to fine-tune your machine to different 
welding conditions which you will encounter.  Light sheet metal is much 
tougher to work with than plate and structural steel and takes a lot more 
practice and skill to do well.
Bottom line is that it is unrealistic to expect someone with little or no 
welding experience & training to simply go out an buy a cheap welding 
machine, with limited adjustability, bring it home, plug it in and do 
acceptable quality welding on autobody steel.  The good news is that it's a 
skill that most of us can learn, given a bit of patience and a lot of 
practice.
Oh, and Jim.......yes, God made autobody sheet metal thin and easily warped, 
plus gave man the urge to brew and drink beer for a very specific reason, 
which I'm pleased to see you are aware of ;)
Bud Osbourne
----- Original Message ----- 
From: "Jim Johnson" <bmwwxman at gmail.com>
Cc: <spridgets at autox.team.net>
Sent: Wednesday, December 09, 2009 9:45 PM
Subject: Re: [Spridgets] mig welder


> On Wed, Dec 9, 2009 at 7:49 PM, <james.f.juhas at snet.net> wrote:
>
>> Particularly with sheet metal, the duty cycle on my SP100 never catches 
>> up
>> with me.
>>
>
> I just bought a cheapo MIG just to use on sheet metal.  I looked at duty
> cycle but decided that having it catch me was a Godsend.  The perfect 
> reason
> to take a break and pop a brew...   ;-)
>
> Cheers!!
> Jim