Subject: FAQ: Which MIG welder

From: [email-masked] (Jim Kirkpatrick)
Date: 27 Jun 93 14:21:57 MDT

There was recently a discussion on MIG welders, and
the suggestion that the material be gathered up for
inclusion in the FAQ.  I've tried to edit some of it
down a bit, and what follows is the proposed question
"Which MIG welder should I buy?" and the answer.  Let
me know of any suggestions.  I'll try to stuff this
into the FAQ next time.

Jim

nn.  We frequently see "What should I buy" questions; one example
     is "What MIG welder should I buy?"  There is no definite answer,
     and the prospective buyer should read the other entries in this
     FAQ regarding welding.  What follows is an example of such a
     question and the answers received (June, 1993).  We claim no
     responsibility for correctness or liability for your money!

     Keith King asked:

      I'm looking at the purchase of a MIG welder for auto body repair and
      other light welding jobs around the homestead and I don't have much 
      background on this type of equipment.  

      The models I'm looking at are the Lincoln SP-100 and the Miller 130.
      Both models are 110v portables.  The Miller has a higher rating but
      I'm not sure if that's critical for my applications.  The Lincoln has
      the advantage of having infinitely variable power output vs. stepped
      output for the Miller and the salesman said the gun on the Lincoln
      was a "Tweako?" whatever that means.  Both units are similarly
      priced/warranted etc.

      Century has a bunch of lower priced, shorter warranty, cheaper looking, 
      MIG welders.

      Does anyone have any experience/opinions on these welders or other MIGs
      to help me make a more informed purchase.

     Jim Narem answered/asked:

      I'm also interested in MIG welders for sheet metal and roll bar
      work.  I've used the Italian made SIP 110V MIG unit.  It works; it was
      worth $100 (purchased at some close-out sale) but not the $350 that
      places want retail.  It's tough to get parts; even the tips have to be
      ordered.  The wire feed mechanism sucks.

      I've seen some new Lincoln's on the market; both are wire feed
      welders with optional MIG kits as opposed to the SP-100 and SP-130
      which are purpose build MIG units.

      Lincoln Weld-Pak 100, 88 amp, 18V @ 20% duty, 110V, $354 w/MIG kit.
      Lincoln Weld-Pak 125, 130 amp, 20v @ 30% duty, 220V, $556 w/MIG kit.
      (Prices are Connecticut Home Depot, tax bandit not included)

      The MIG kits are about $80 each, they have a gas flow regulator,
      solenoid and (I think) a different gun.

      Does anyone have any experience with these welders?  They seem cost
      effective compared to the SP-100 and SP-130 but I'm nervous since
      Lincoln seems to be releasing some home/consumer grade equipment (like
      their new AC arc welder with the cheezy variable amperage control).

      There are also several Century MIG units commonly available at large
      home improvement shops (yup, WELD on that new addition).  I've used
      their AC/DC arc welder and was impressed with its cost/performance.
      Has anyone used any of the Century MIGs?

     Ken Clarke answered:

      I took an evening welding class at a technical high school (10 weeks)
      and got to try various types of welding (stick, MIG, TIG, and
      oxy/acetylene.  Also got some good tips on safety, and on how to by a
      MIG welder.

      The instructor spoke of the "big three" in the welding business
      (Miller, Lincoln, and Hobart). He was a confirmed "Miller" man, but
      we used Lincoln (and Airco) welders in the tech. school. I now think
      that it makes sense to buy whatever you decide to buy at your
      favorite welding supply store. The guys there have lots of good
      advice and if you go with one of the big three, you will not have any
      problem getting parts and consumables for your welder.

      I looked around for a while and compared the 110v portable welders by
      Lincoln and Miller and Hobart. My favorite welding supply house was
      having a "package deal" that included the Hobart Handler 120.
      Included in the package was the welder, a 2 lb. spool of .024 wire, a
      Jackson welders mask with the 4x5 face plate (get a number 10 shade),
      a *good* pair of welders gloves, a 55 cu. ft. tank of shielding gas
      (C25 which is 25 percent CO2 and 75 percent Argon), a dual-gauge
      regulator and connecting hose. This was about 1.5 years ago and I
      believe I paid $625 for the package.

      The Hobart has been great. It works fine on auto body panels and I
      have also done work on exhaust systems, mailbox posts, minibike
      mufflers, lawnmower parts, and am finishing up a trailer axle for a
      friend this weekend.

      So, I guess I'm advocating the Hobart, but if you can get a good deal
      on the Miller or the Lincoln, those would probably be fine, too.

      A few of the features on the Hobart that I liked were:

      1. A "purge" feature, that allows you to set the flow rate on the
         shielding gas without spooling out wire.

      2. The wire feed mechanism that lets you set the tension on the drive
         wheel but also lets you change wire spools without moving the
         setting.

      3. The ergonomics of the unit, the way the wire spool goes in, the
         way the lid hinges down (not up like the others).

      4. Five year warranty on power diodes and SCRs, three years on major
         components and one year on parts and labor.

      I would stay away from the Century welder. I don't think it has the
      quality of the "big three". I think you would have trouble getting
      parts, probably would have to order them. All parts for the big three
      can be had at local welding supply houses, in-stock. Also, the
      "Tweeko" comment is referring to the gun end of the welder. I hear
      that it's suppose to be a very common industry-standard type of part.
      Parts for the Tweeko handle/gun should be available at any welding
      supply house.

     Jim Swonger answered:

      "Tweako" is actually Tweco, a manufacturer of MIG and TIG handpieces
      and such.  What this means is that parts are pretty readily available;
      they're everywhere.

      For sheet metal welding you'll run nowhere near the maximum heat setting
      on any machine.  On my 160 I'm down on "2" for heat.  The higher current
      machines of some of the cheaper brands need to be looked at carefully;
      some of them have -very- low duty cycles, leading me to believe that the
      critical parts are not much, if any, better than the cheaper models.

      The "purge" feature is good to have; however if you do not find a machine
      with it you can add it pretty simply. An auxiliary control switch for the
      solenoid valve is all it takes, in parallel with the relay that runs off
      the gun trigger.

      For serious sheet metal work spot and stitch modes are very nice
      amenities, allowing you to tack up a large piece with spaced short
      beads, minimizing distortion and allowing a fast, even hand motion.
      You can get by without it, but if it comes free or cheap...

---

From: [email-masked] (Ken Clarke)
Date: 30 Jun 93 23:39:25 GMT

In article <[email-masked]> [email-masked] (Tom Bereiter) writes:
>
>In article <[email-masked]> [email-masked] (Jim Kirkpatrick) writes...
>>inclusion in the FAQ.
>This is good start, but from my point of view the confussing things are
>well beyond "is brand X a good machine".
>
>  1) what does does duty cycle mean.  i.e. is 200amps at 60% duty good or bad?
>  2) inverter or transformer model?
>  3) what type of gas. CO2 or argon/CO2?
>  4) can a MIG be modified to do stick too?
>  5) can a MIG weld s.s. and alum. or do I need a TIG?
>
>Anyone have more or want to take a stab at answers?
>
>Tom.

It's my understanding that duty cycle refers to how long you can weld
continuous (at max. rated current?) vs. how long you have to
wait before welding again.  A duty cycle of 30% would indicate you
could continuously weld for 3 minutes, wait for 10 minutes then weld
some more.

I assume you're refering to a system that's AC or a system with power
diodes that makes DC. I prefer a DC system which allows one to change
polarity. Changing polarity (having the electrode DC positive or DC
negative) allows the heat of welding to be directed more towards the
electrode or the weldment. With AC, you don't have this choice. Also,
I've heard that an AC system (especially the "buzz-box" arc welders
on AC) tend to have more splatter while welding as compared to
running them on DC. Working with thin metal like auto body panels,
it's advantageous to be able to localize the heat and minimize
warpage while welding.

CO2 is cheaper to use than the C25 mix (argon/CO2). Pure argon is
truly inert and does the best job at shielding the weld from
contamination by the air. C25 is almost as good and is cheaper than
pure argon but is not truly inert. The CO2 in the mix will react a
little with the weld. Pure CO2 will react even more with the weld. I
would use C25 to weld mild steel and stainless steel. Welding
aluminum really requires pure argon.

I'm not sure why you would want to modify a MIG system to do stick
welding. A MIG unit can do anything that you could do with a stick
welder and more. With a MIG, you don't have to stop and replace the
electrode periodically. And you don't have to chip the slag you'd
get from a stick welder. You can MIG weld continuosly as long as the
wire and shielding gas holds out (and until the duty cycle timer or
temp sensor kick in).  Flux-cored wire is also available for MIGs.
This can be used instead of a shielding gas and in some cases
(welding outdoors on a windy day) is preferable to using a separate
shielding gas. You do get a little slag with the weld, but not bad.

Wire is available for MIGs to do mild steel, stainless steel and
aluminum welding. Again, you would need pure argon for MIG welding an
aluminum piece with aluminum wire. The aluminum weld will not be like
the weld you would get using a TIG machine, but with sufficient
practice, a good weld can be had. Aluminum is pretty much an exotic
metal to weld. It really takes a bit of skill to get a good aluminum
weld using MIG or TIG.

________________
Ken Clarke

---

From: [email-masked] (James W. Swonger)
Date: Thu, 1 Jul 1993 13:09:22 GMT

>  5) can a MIG weld s.s. and alum. or do I need a TIG?

 Duty cycle is the percentage of a time period (typically 10 minutes) that
the arc can be run at a given current level without damaging the machine.
Typically a machine will have 100% duty cycle up to some fraction of its
numerical rating (maybe halfway or so, less if its manufacturer is into
specsmanship). Beyond that they may specify a fixed duty cycle or a duty
cycle that falls off with increasing current; it depends on thoroughness
mostly. In the example given, 200A@60%, that's a whopping big MIG. Ratings 
like 50A@100% and nominal 120A@30% are more run-of-the-mill. 

 Inverter models are intended to run off DC, either a battery (set) or 
rectified line current. They may be more efficient than transformer models
especially at lower currents, and certainly lighter since the inductors
will be much smaller. They may give finer heat control. On the other hand
I tend to think the simpler transformer designs are more robust. The 
portability of inverter MIGs is probably their biggest selling point. 
Lots of on-site repair work doesn't have a dryer plug handy.

 Typical hobbyist gases are either Argon or 75%/25% Argon/CO2 mix. MIG
gases for production use have numerous formulations, typically the addition
of small percentages of O2 or H2 to make the shielding gas slightly 
oxidizing or reducing to optimize weld quality for a specific material.
Argon is the most general-purpose, and makes the welds on plain steel 
"sit up" a little higher (less penetration); from cutaways I have seen 
the Argon penetration may be deeper but only in a narrow region; pure
CO2 makes a wider, rounder penetration which is more likely to lead to
blow-through on thin material but may give a better union of roughly
mated pieces. Argon is the only gas to use for aluminum and is better
than the mixture for stainless, where the alloy metals may react with 
the CO2 leaving soot and oxides. For the home welder an Argon bottle is
the way to go.

 A MIG unit is not appropriate for stick welding. Stick requires a 
constant-current source (typically a saturating inductor) at medium
voltage (50-100V, depending on degree of arc stability etc; 2-range
AC boxes usually get there by using 2 voltage taps off the same core).
MIGs require a constant voltage supply which is usually around 25-40V
or so. The two are basically opposites. Besides, with buzz boxes in 
every pawn shop, it'd be easier and probably as cheap to pick up a
utility buzz box for those times when a dirty weld on material thicker
than 1/2" is something you really want to do.

 A buzz box may be used for TIG welding is you're willing to accept some
limitations and have the gas, regulator and torch.

 MIG can weld any material for which somebody has seen fit to produce 
.030" wire. Mild steel, stainless and aluminum are readily available. 
Specialty wires, like hard surfacing alloys, are more trouble to obtain
and often come in minimum 10-lb spools or larger. Large spools may 
corrode before they get used up; dry storage of any welding consumables
is important for hobby welders who don't run through material at a high
rate. 
-- 
##########################################################################
#Irresponsible rantings of the author alone. Any resemblance to persons  #
#living or dead then yer bummin. May cause drowsiness. Alcohol may inten-#
#sify this effect. Pay no attention to the man behind the curtain. Billy!#

---

From: [email-masked] (Ken Clarke)
Date: 1 Jul 93 13:36:38 GMT

I need to ammend a comment I made on "duty cycles" of MIG welders.
After looking back in the literature that came with my Hobart MIG
welder, they define duty cycle as "... the percentage of each ten-
minute period of time that the welding machine may be operated under
rated load conditions. For example, a duty cycle of 30% means that
the machine can be operated at rated load for an average of 3 minutes
of each 10 minute period of operation. During the remaining 7
minutes, the machine must idle to permit proper cooling."

The rated output amperage of my Hobart Handler 120 is 90 amps DC with
a rated duty cycle of 30%. The Hobart literature includes a graph
that shows duty cycle vs. weld amperes. Up to 50 amps, the duty cycle
is 100%. It tapers off down to 30% at 90 amps "rated output."
However, the curve keeps going all the way to 120 amps which shows
about a 17% duty cycle. In the promotional literature it states the
90 amp rated current with the 30% duty cycle, but also states a
current range from 30 to 120 amps.

In real practice, I've never been close to the "rated output" on my
MIG. There are five "coarse" current settings on my unit (along with
a variable wire speed/current control) and I've only used the first
two for the all the welding I've done. I welded a friend's trailer
axle that had 0.25 inch thick steel pipe and still had it on just the
second setting.

So, when comparing MIGs, I guess one can look at the rated output
current, rated duty cycle, and overall current range. I think that
some manufactures may tend to be more conservative in their ratings
than others, so you might take the data in promotional literature
with a grain of salt.

________________
Ken Clarke
[email-masked]

---

From: [email-masked] (Jim Kirkpatrick)
Date: 1 Jul 93 08:56:41 MDT

>   5) can a MIG weld s.s. and alum. or do I need a TIG?
Note that there is a separate discussion on welding elsewhere in the FAQ,
such as questions 17 and 18 of the current FAQ.  18 in particular has a
short discussion on what type of gas.  However, most of the above could
easily be added (if answers show up!).

Thanks for the suggestions.

Jim

---

From: [email-masked] (Kirk Hays)
Date: Thu, 1 Jul 1993 15:32:01 GMT

In article <[email-masked]>, [email-masked] (Ken Clarke) writes:
|> I need to ammend a comment I made on "duty cycles" of MIG welders.
|> After looking back in the literature that came with my Hobart MIG
|> welder, they define duty cycle as "... the percentage of each ten-
|> minute period of time that the welding machine may be operated under
|> rated load conditions. For example, a duty cycle of 30% means that
|> the machine can be operated at rated load for an average of 3 minutes
|> of each 10 minute period of operation. During the remaining 7
|> minutes, the machine must idle to permit proper cooling."

So, if you beef up the cooling system, can you up the duty cycle?  Are the
machines equiped with a thermal cut-out switch, or a timer, or are you on the
honor system?

-- 
Kirk Hays - NRA Life, seventh generation.
"The only thing necessary for the triumph of evil is for good men to
do nothing."  -- Edmund Burke (1729-1797)
[I do not speak for Intel, not being an officer of the corporation.]

---

From: [email-masked] (Jim Kirkpatrick)
Date: 1 Jul 93 09:14:24 MDT

> could continuously weld for 3 minutes, wait for 10 minutes then weld

If it's a percentage, I would assume 3 minutes on, 7 minutes off.  In
actual practice, though, it probably varies widely and depends on other
conditions such as ambient temp and wind.  Unless an overheat cutoff
is a required feature, it would probably be an option worth checking
for when shopping.

> it's advantageous to be able to localize the heat and minimize

Would it be safe to say that directing the heat towards the electrode
reduces warpage in sheet work, but introduces a danger of overheating
the handle?  Or is it simply the warp issue?  I assume the opposite
effect is normally desired in non-sheet work, but why?

> CO2 is cheaper to use than the C25 mix (argon/CO2). ...

I have also heard of A75.  Is A75 and C25 the same thing?

Jim, updating the FAQ as we "speak" ...

---

From: [email-masked] (Ken Clarke)
Date: 1 Jul 93 18:30:51 GMT

>machines equiped with a thermal cut-out switch, or a timer, or are you on the

My MIG unit has a "thermal overload device" that turns the machine
off if/when things get too hot inside the MIG. It resets itself
automatically after the machine has cooled.

An internal fan comes on and runs continuously when the MIG is turned
on. There seems to be lots of air flow inside the MIG. I've never had
it cut out on me. I suppose that one could provide additional cooling
and theoretically increase the duty cycle.

I still think that published duty cycles have varying degrees of
conservatism from one manufacturer to the next.

______________
Ken Clarke

---

From: [email-masked] (Ken Clarke)
Date: 1 Jul 93 19:10:11 GMT

>Jim, updating the FAQ as we "speak" ...

You're right, Jim. A subsequent posting of mine ammends "30% duty
cycle" to an average of 3 minutes on, 7 minutes off over a 10 minute
period.

I don't think there's much danger of overheating the MIG handle. They
seem pretty rugged and under normal conditions air cooling should be
sufficient.  I know that TIG handles get hot enough to require water
cooling, though.

The literature that came with my MIG recommends using DC electrode
positive (DCEP) for all solid wire welding, and DC electrode negative
(DCEN) for the flux-cored wire. Not sure why. They refer to DCEP as
"reverse polarity" and DCEN as "straight polarity".

Hobart also refers to C25 as 75% argon, 25% CO2. I'd be willing to
bet that A75 is the same thing just designated differently by another
manufacturer.

_______________
Ken Clarke

---

From: [email-masked] (Tom Bereiter)
Date: 6 Jul 93 14:29:42 GMT

Thanks to those who responded to the questions I posed.
 
This April I went to the American Welding Society show in Houston.  I had
hoped to find a good "show" deal on a MIG or at least get the chance to
kick the tires on a few models.  The big three (Miller, Lincoln, and Hobart) 
were there, but so were the little four dozen.  It seemed that every other 
booth was some maker of MIG welders.  Rather than clear matters up, all 
talking to the vendors did was leave me with a stack of spec sheets and 
conflicting claims.  These were the origin of the questions I posted. 
 
In article <[email-masked]> [email-masked] (James W. Swonger) writes...               
>In the example given, 200A@60%, that's a whopping big MIG 
 
Yes, and it's sitting in my garage.  I found a 10 year old Millermatic 200 for
sale last week. I've always found industrial tools to be a better value than
home-shop or body-shop tools.  How do I know the Miller is industrial?  It has
the center hook for suspending it from a crane overnight.
 
A couple more notes on the show:  Plasma cutters seemed to be the big
thing this year.  Typical was to have a welder, in full protective gear,
sitting in a booth talking about the virtues of a particular machine.  He'd
then make a slagless cut through 1" steel to prove the point.  They handled
eye protection by having a filter shield which could be raised to enclose the
cutting booth on three sides.
    Also big, in every sense, were the computer controlled cutting tables.
One had a CAD screen on which the operator could draw a shape with a 
joy stick (I guess a mouse won't hold up in the factory).  With the press
of a button the machine would then cut the corresponding shape out of
steel plate.  One enterprising vendor at a nearby booth had picked up
a bunch of these cut-outs and was using them to show how his grinder
disks could but a mirror finish on plain steel.

Tom.