need expert advise

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Hi guys,Granpa Marc needs your expertise!I have a rough brass ( at least I think it is ).very heavy casting of the windshield posts for a car I am building.There are several imperfections that need to be filled before it can be chromed.I was told that I need to fill this with hard silver solder.I found some on ebay and was also told that what I had would work.I am having a terrible time getting it to flow even after useing exteme heat for a very long time.I am also useing liquid instead of paste before applying. Why do I need the hard silver instead of regular silver solder?What am I doing wrong to be having so much trouble with getting it to flow and make a secure bond?Why can't I just use brass rod? Thanks for any help on this.Best regards,Grandpa Marc
Reply:Firstly you should be using paste flux, not liquid. You are just burning off the liquid far in advance of brazing temp.Hard silver leads me to believe high strength or high temp silver, which is mostly needed for hard steels of  chromium alloy steels. I would try sil-phos filler first(plumber's grade), as it melts at a low temp and is cheap compared to high silver braze alloy. Get it at the hardware store. See if it leaves porosity. Good LuckWeld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Brass filler won't work because it melts at the same temp as your base metal. You need a filler that melts at a much lower temp. Or arc weld it.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:I suspect the problem you're having with getting the silver solder to flow is that the brass is conducting the heat away so fast that you can't "catch up to it." As an alloy of copper, brass is super conductive of heat, so you really need to put the coal to her to get the solder to flow. When I've tried to silver solder things to heavy pieces of brass, the only way I got it to work was to blast it with heat FAST with a TIG torch. I think I set the panel at 200A or so and then floored it with the arc going to the brass until the nearby solder melted, then got out of there before the zinc in the brass boiled off. If you're trying to do it with O/A, I think I'd use the biggest tip I could get away with. The more BTUs per second, the better. It's surprising how much, and how fast, heat wicks away with brass.It goes without saying, but you also want everything clean clean clean.Good luck.
Reply:Belay my earlier recommendation of sil-phos. That is better suited for tig.Is your plater asking you to use 56% safteysilv(cad free)?  Cad free silver alloy flows for crap. 56% is the only one that comes close, and the melting temp is good. Otherwise I would choose 35% with cadmium. And white paste of course.You can get them here. http://www.mcmaster.com/#silver-brazing-alloys/=mafc5vWeld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.