N00B question on wire sizes

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As I have just purchased a MM251 with no gun, I have been looking at those offered by my LWS and FleaBay.I've done a lot of MIG welding but never replaced a gun before, only replaced parts like-for-like which may not have been the right thing to do.  Basically my knowledge of how it works BEST might be wrong.I am finding a lot of Bernard guns for 0.045" wire (centerfire) in the 300A range, that will work for my application.  I DO NOT want to overheat a smaller gun, been there, done that.The MM251 comes with drive rollers for 0.030" and 0.035" wire and I'm pretty sure I have no real reason to use larger than that on my 1/4" and smaller hobby stuff.From what I understand, you want the liner to be slightly larger than the wire and the tip must match.  So, I would need to buy a 0.035" liner for my "new" Q30 gun?  I know it can use the 0.030" tips.Do I understand this correctly or am I all confused (again)?Thanks!JohnGMillerMatic 251
Reply:I just found a table that listed duty cycles for various guns, it appears that the Q20 is more than adequate for the MM251 as the ratings of the Q20 excede those of the welder somewhat.The fact that this will slmost never be used anywhere near 50% duty cycle and I doubt over 200A should make the Q20 more than adequate.I really don't think the larger 0.045" wire is a good idea, I'm thinking 0.030" is what you want for general welding and maybe 0.035" if the material is thicker.  It also seems like the guns come with one size liner, ie: Q20 with one, Q30 another etc, regardless of the wire used.  Is that right?????JohnGMillerMatic 251
Reply:The Q300's on ebay usually come with the .035/.045 liner.  Liners are not that much money if you want the smaller .035 liner to run .030 and .035 wire just order it at your local weld shop.  You can switch out liners sizes in the QGuns at will, just look up the part number the Bernard website, www.bernardwelds.com.  You'll pay alot more money for a brand new Q200 ordered through the local weld shop than what the Q300's cost on ebay so the ebay Q300's are definately the better deal.   You can use the 200, 300 or 400 on your machine and they will all work equally well unless you're doing spray.  For spray, get the 300 or 400.Your machine will burn .045 wire just fine, but .035 is the better size for most of what you'll likely be doing in general repair and fabrication.   Use .023 for thin sheetmetal.Last edited by DesertRider33; 01-24-2010 at 12:00 AM.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:.035 is probley what you want unless you plan on welding alot of thin stuff.030 will weld 1/4 inch and beyond but your going to be pushing alot of wirewith a .045 liner you should be fine you shouldnt have problems running .035 wire though itor .030 for that matteri would probley get a q30 gun for itthe q20 is abit small I have used a q40 on a 251 and that is a good setupusually the rating is based on running co2 not a mixed gasif you plan on welding thin stuff use .030 but typically if you walked into most welding shops you would find .035 in the machine unless they are welding structural steel or heavy metalif you plan on welding light metal i would setup for .023 and .035 this will enable you to do sheetmetal as well as weld some pretty thick metal
Reply:I run .035 exclusively in mine.  I do anything from welding a roof back on a race car (very tough with .035) to 3/4" or 1" plate.My name's not Jim....
Reply:welding anything thinner than .065 takes some dingling with the machine sometimes its quicker to switch wire than get it to weld nicely haha
Reply:Thanks guys!Because I don't work on welders I was thinking that the liner and wire size needed to be matched.  From the responses, the Q30 will have a 035/045 liner  - one that will work for both, I run with it and thanks again!JohnGMillerMatic 251
Reply:If you are not going to be running .045 wire, the .035 liner will feed the .030/.035 wire better down the 15' torch lead than the .045 liner.  This is in my experience with my 3 machines that use 15' Q300's.  The reason the .035 liner feeds the small wire better is because the larger .045 liner allows the small wire to 'snake' inside the liner, which can result in pulsing of the wire speed at the gun end as the wire snakes up and spring back inside the liner.  On my Passport with Q300, I run .035 and .030 wire, no .045, so I put in an .035 liner in it and it works much better than the .045 liner, especially when the torch lead is going all different directions to get to various weld locations on-site.   On my 350P with Q300, I run mostly .035 so I use an .035 liner in it too and change to the .045 liner when I change to .045 wire.   On my Suitcase with Q300, I run .045 and 1/16 wire and keep the 1/16 liner in it.  The .045 wire feeds fine in the 1/16 liner cause it's thicker and stiffer than .030/.035 wire and doesn't snake as much inside the bigger liner.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:DR,That makes good sense and since I cannot imagine needing 045 wire in my application your advice is well appreciated.JohnGMillerMatic 251