Plasma cutter backfire?

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I'm the main weldor/fabricator at our garage. At the moment our project is a 66 Mustang. We're almost done with the roll cage. I wanted to use the plasma cutter to cut out the floor pan, but our mentor said cutting through rust would cause the machine to backfire and set me back $1000 to replace it. My question: Is this really true, cause I don't really feel like coughing up a grand at the moment. (I already cut the floor pan out with a sawzall, I just want to know for future reference.)Here's a link to our site. www.garageknights.orgI've also attached some pictures of the car. Attached Images
Reply:News to me. Backfire eh never heard of such a thing.Cutting through rust will sometimes cause the tip to burn up faster, but that should be $2.00 not $1000.00
Reply:I've not heard of that one yet either.  I've cut rusty and painted metal, etc with my plasma and the thing still works fine.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:say what?  never heard of such thing.  i've did some dirty work with a plasma with no troubles.Daye
Reply:Chi-com plasma cutters have been known to "back-fire" when you first plug them in but only once. Nice looking work BTW.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:I have cut some pretty nasty stuff but besides going through consumables faster no back fires. Just make sure you have a good clean ground or it can be a pain to start.Vantage 300 kubota ,miller 304 xmt ,lincoln ln 25 pro , ranger 305 G, plenty of other tools of the trade to make the sparks fly.
Reply:No such thing as a backfire. Cutting through rust and painted metal is a piece of cake. Some of the cheapo plasma cutters will eat up consumables when cutting nasty metals, the better brands (Hypertherm, Thermal Dynamics) will perform much better.Jim colt
Reply:No "backfire" here either.Maybe what he was refering to was a 'lower-end' machine losing the arc connection (similar to when cutting through expanded metal or any other 'interrupted' cut).  Low-end machine might lose the arc and then you have to retrigger/restart the arc.  Annoying and eats up consumables.The 'better' machines seem to handle 'interruptions' (rust, expanded metal, seams or other small gaps, etc) with no real problems.  The best laid schemes ... Gang oft agley ...
Reply:Backfire? Where did this guy learn this from? lol  Keep your tourch back a tad (stand-off) and dont fire the plasma in mid air as it can mess the tips up. Also water is not good to have in your air supply. As for what that dude said, never heard of that. I have used a plasma a lot including CNC plasma burning machines through some pretty rusty steel and had no problem. Tips just wear faster sometimes.
Reply:Well everyone seems to be on the same page. So i'll just add this. You need a new welding and fab mentor.
Reply:I showed him this thread, and got the OK to use it on rusty metal.We got most of the roll cage installed. Next up is body work and then we'll be moving on to the engine. I'm not entirely sure about which one like a 351 or a 302 but I know we'll be super charging it. The trany is going to be a C4, we're shooting for the 750 HP range.Here are some pictures, we put the Lincoln welders in the photo cause they've donated some stuff  (Helmet) Attached Images
Reply:Ouch that's a lot of cancer in the back fender I'm glad they don't salt the roads down here.Dynasty200DX w/coolmate1MM210MM VintageESAB miniarc161ltsLincoln AC225Victor O/A, Smith AW1ACutmaster 81IR 2475N7.5FPRage3Jancy USA1019" SBAEAD-200LE
Reply:Originally Posted by AndyAOuch that's a lot of cancer in the back fender I'm glad they don't salt the roads down here.
Reply:Just remember, even tho the plasma does just fine on rusty/dirty/painted metals it is critical that the work lead be connected to a cleaned surface. I think that's where these ideas that it doesn't work come from. You can't be clamping to shag nasty flakey rusted stuff and expect that it's going to cut right."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