MM175...how thick can I go?

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Just wondering if any one uses a smaller machine for doing thicker projects sometimes.  I just got a nice MM175 and wanted to know how versital it really was!
Reply:The MM175 is a solid machine thru 1/4" steel. You can probably push the limits a bit if you bevel and weld both sides. Safely, maybe another 1/8". I really wouldn't choose that machine for material much thicker than that, and if it was for something critical like a hoist frame, I'd error on the side of caution and probably not even go as high as 1/4" to be safe.A good part of this will come down to the skill level of the operator. Someone with a lot of hood time and skill with mig will be successful welding thicker material than someone with limited experience. The extra amps  of a larger machine will go a long way towards helping get good solid welds for those who lack as much skill and experience. Keep in mind the thicker that material, the more heat will be sucked away from the weld joint increasing the chances of getting poor penetration into the base material. Mig is notorious for making pretty welds with little to no penetration when used beyond it's practical limits. This is especially true with smaller migs like 110v units, but also true with the mid sized or smaller 230v migs if pushed too much.I'm talking of course about welds where it counts, not simply sticking metal together for an art project or BBQ grill..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:I started out w/ a MM130 for auto body repair. As a last resort I could weld 3/8" steel brackets etc if beveled and preheated with an oxy/fuel torch."Steel is weak. What is steel compared to the hand that wields it?"- James Earl Jonesmiller 225 w/ 3035spoolmate, Lincoln sq wv 275 w/radiator, hypertherm 600 plasma cutter, other stuff
Reply:Keep in mind that the overall size of the weldment has a big affect as well as the joint design. Little one off do-dads heat up quickly and easily, big pieces suck it up. That can be the deceiving part of grabbing some little cut off for a test weld then moving on to the big iron to do the actual weld. Then an open outside corner is different than a T configuration by a whole lot. You can blow the heck out of an outside corner and make yourself feel like you've got power to spare then move to a T with no joint prep and not get much more than a thin layer of fusion."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:So if you bevel the edges enough or do a preheat, you could possibly do 3/8 with multiple passes?  I'm just wondering how and where I will be able to use this machine if it comes up.
Reply:Maybe. Like many things, sometimes a little information is more dangerous than no information. This is especially true with newer welders who are trying to stretch the capacity of smaller machines. For most of these welders more amps is a better solution. That means a larger machine, or limiting themselves to projects that use thinner materials.Yes a bevel and preheat will in some cases help. However most newer welders don't know what to look for to tell if what they are doing will get them a decent weld or not. There's a bit more to it than simply beveling a joint, pouring heat to it and then running a bunch of beads. None of this will solve poor welding technique. In some cases more weld or too much heat can be worse than simply a poorly penetrated joint. Newer high strength steels like are often found in vehicles, don't take excess heat well. too much heat will weaken the metal itself. Your weld may hold, but the material will fail due to excess heat.Again all this is assuming we are talking about welds where performance counts. Say on a trailer, overhead hoist frame, etc. where you need to be able to do code quality welds every time. Many hobby projects don't require this level however. You don't need perfect welds to attach a piece of 3/4" steel to the top of your table, or to use some 1/2" angle to build a welding cart. If the hinges on your BBQ grill fail, chances are no one will get hurt, same with say a piece of yard art. Your weld should be fairly solid however if you build  a railing for a second floor deck, but for a yard fence it's probably not as big an issue.Best suggestion is to stick to the recommended limits given by the manufacturer for you machine, or in the case of smaller 110v machines, less. Keep in mind if Miller thought this machine was capable of 3/8", they'd say so. If you want to know if a machine is capable of doing say 3/8", the best way to find out is to do what industry usually does. You run a test bead under similar conditions and bend test it at a minimum.  A bend test is not beating the F out of it with a hammer. It's running it thru the same basic test the AWS uses to certify welders. CEP here has done some decent posts on bend tests here in the past. A search will bring up all sorts of info on this if you want. Most hobbyists can't pass a bend test even if the machine was capable of welding 1/2", especially if the weld is done in anything but the flat position. Vertical and overhead are almost always guaranteed fails unless you really practice quite  a bit and know what you are doing. Fancy "tricks" won't overcome poor welding skills..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:I'm just not that familliar with mig.  I have been stick welding my whole life.  Thank you gus for the good information.  I got a fairly good deal on the MM175 and was just wonderng what is was truly capable of if done correctly.
Reply:DSW, is it known how depth of fusion quantitatively varies as to preheat temperature and welding current? I've never seen such data but such  would help me more clearly understand the limits of various machines, as an alternative to "just believing" none but the high power ones can provide adequate "penetration" for "thick" applications. Please note I'm not talking about "penetration" per se (since any 110V machine can achieve a "full penetration" weld just by opening up access to the joint, e.g. bevelling) but the depth of that weld zone beneath the base surface where fluid mixing actually takes place. That seems to me very definitely a function of temperature and amperageLast edited by wirehead; 12-04-2011 at 02:56 PM.XMT304 (school)SP125+ (home)HF 4x6 BandsawGood judgement comes from experience and much of that comes from bad judgement.
Reply:Andcon, I have a MM175 also. When I have to weld anything over 1/4" I plug in the old thunderbolt so there's a lot less doubt about weld quality/strength. If you've been stick welding for a long time then you know what it takes to make a strong weld.                                  MikeOl' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:I'm not aware of any such info, but that doesn't mean it doesn't exist some where. Lots of this is going well beyond "basic". I'm sure there are formulas that a welding engineer can use to determine how many amps at X is needed when material Y thickness is heated to Z degrees... That's what they went to school for and get paid big bucks to do. I have enough trouble remembering what little I learned in basic structures dealing with very basic weld design. Theoretical math always gives me headaches. I was always better with applied math myself.Taking a quick look in Lincoln's book "The Procedure Handbook of Arc Welding" ie "The Bible" In section 3.3-3 under preheat, they give a formula that links kilojoules/in, with arc voltage in volts, weld current in amperes and arc speed in in/minute. Above that formula.. Whatever the method used to estimate preheat temperature, the value obtained should be confirmed by welding tests on simulated or actual assemblies before it is committed to production welding.
Reply:Thanks for the thoughts and good luck with the code. You can download the 2010 AWS D1.1 somewhere on the internet. It's a tome (569 pages) and was not really helpful (to me) as the parameters for my "weld test" were, outside of specifics for joint geometry, "as normally specified by the equipment manufacturers" or some such vaguery. It was a "pre-qualified" procedure I was performing.XMT304 (school)SP125+ (home)HF 4x6 BandsawGood judgement comes from experience and much of that comes from bad judgement.