metal prep/ rusty metal

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Hi,I'm in the middle of a "restoration" of a 1973 BMW. Most of the work I'm doing involves elimination of rust, cutting out panels and patching in new metal.A few questions:What is the preferred too of choice for cleaning the weld area?(Grinder with grinding wheel, grinder with sand paper disc, drill with wire wheel, etc, etc)Which method works best for you??Is there a chemical that prepares the metal for welding, much like a flux for soldering ??In a lot of cases, the metal never gets the bright, shiney appearance, but rather a brown rust color, despite grinding it to death. Will the weld hold to this metal, or only the bright, shiney, new looking metal??Lastly, in areas that cannot be clamped, I have used pop rivets to secure the metal while I weld. Is there a compelling reason why I should NOT be doing this??Any tips and suggestions relating to the above questions would be greatly appreciated.Thanks.
Reply:Originally Posted by laldogHi,I'm in the middle of a "restoration" of a 1973 BMW. Most of the work I'm doing involves elimination of rust, cutting out panels and patching in new metal.A few questions:What is the preferred too of choice for cleaning the weld area?(Grinder with grinding wheel, grinder with sand paper disc, drill with wire wheel, etc, etc)Which method works best for you??Is there a chemical that prepares the metal for welding, much like a flux for soldering ??In a lot of cases, the metal never gets the bright, shiney appearance, but rather a brown rust color, despite grinding it to death. Will the weld hold to this metal, or only the bright, shiney, new looking metal??Lastly, in areas that cannot be clamped, I have used pop rivets to secure the metal while I weld. Is there a compelling reason why I should NOT be doing this??Any tips and suggestions relating to the above questions would be greatly appreciated.Thanks.
Reply:Sand blasting is good, but becareful how much pressure you use and how long you leave the gun on the area. Too much pressure and/or time and you will warp the steel. We used plastic pellets at a mold shop I worked at to clean the molds that has a hard chrome finish. I decided to try to clean up some old parts I had. Worked like a charm. We got the stuff through Media Blast I think. MC/2 I believe. Kinda pricey, but workd really well.Tony"Wherever you go....there you are"
Reply:Originally Posted by orphan68Sand blasting is good, but becareful how much pressure you use and how long you leave the gun on the area. Too much pressure and/or time and you will warp the steel. We used plastic pellets at a mold shop I worked at to clean the molds that has a hard chrome finish. I decided to try to clean up some old parts I had. Worked like a charm. We got the stuff through Media Blast I think. MC/2 I believe. Kinda pricey, but workd really well.Tony
Reply:that about says it all.. ...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:I won't get into the restoration of body metal but my two preferences for rust removal are grinding wheels on a grinder and and flap discs on a both an electric grinder and an air angle die grinder. I can't picture any of the above not removing all the rust or eliminating all the metal in a hurry when body metal is involved.
Reply:RE: "In a lot of cases, the metal never gets the bright, shiney appearance, but rather a brown rust color, despite grinding it to death."There are areas where it will be difficult to remove all the rust; I'm thinking of small pits, multiple folds, hard to access places or delicate spots where removal of the rusted metal would leave little support.  When you don't have to weld these areas but only cover them with body filler or paint, I recommend and use a rust converter - changes to red/brown Fe2O3 rust into hard black magnetite FE3O4.  You can then fill/paint over the converted surface - and the rust does not come through.  Without the converter, the rust seems to reappear within a few months - ruining a time consuming restoration.Rick V
Reply:Go to your local hardware store and buy a bottle of Naval Jelly.  It's a viscous, pink jelly  that you spread on the metal and then wash off.  It's great for removing rust, and you won't have to deal with neutralization of the phosphoric acid.  For really tough rust, use 3M Rolock discs with a 90 degree die grinder.  They're great for surface prep, and they're no where near as agressive as a grinding or flapper wheel.I r 2 a perfessional