From: djb@invalid.com   
      
   On 20/02/2026 19:19, Bob La Londe wrote:   
   > On 2/17/2026 8:52 PM, Snag wrote:   
   >>    I'm going to try my hand at brazing new carbide on some chipped   
   >> and worn boring bars for my mill . I have 3 choices for heat source ,   
   >> O/A , TIG , or my induction heater . I also have a couple of choices   
   >> for braze filler , phosphor bronze TIG filler , regular brazing rod ,   
   >> and silver solder if I can find mine . I also have some brass wire ,   
   >> composition unknown and a few sticks of silphos , though I don't know   
   >> if that will stick to steel . I also have both borax and regular   
   >> brazing flux .   
   >>   
   >>   The plan is to heat and remove the old/broken insert , apply flux   
   >> and a thin piece of brazing filler topped with a new carbide piece ,   
   >> and heat to brazing temp . After watching a couple of youtube videos   
   >> it looks like I may need to hold the new carbide in place as it   
   >> heats/ cools , I'll probably use a piece of SS TIG filler for that .   
   >>   
   >>    I just realized that I can replace the carbide teeth on the face   
   >> mill that came with my milling machine . I tried to sharpen the   
   >> cutters on the lathe , turned out less than optimum . If I do that   
   >> I'll use the indexing device I built for sharpening end mills to   
   >> sharpen them . Might try that to even them up , might turn out I   
   >> don't need to replace them right away .   
   >>   
   >>   Thoughts on heat source and filler selections ?   
   >   
   >   
   > A quick read tells me silver solder 45% silver or higher is considered   
   > "best".   
   >   
   > Silfos (typically 15) is for copper to copper or copper to bronze.  I   
   > have a couple pieces I used for soldering copper tube on an AC unit.   
   > Silfos is nice for copper as it is supposed to be self fluxing, making   
   > out of position work easier in theory.  In reality I only got good   
   > joints on the bench.   
   >   
   > Brass can work, but it doesn't stick to the carbide as well as silver.   
   >   
   > I have a small section of 45% silver solder around somewhere and I can   
   > tell you it was expensive.  I bought it at the a local welding store,   
   > the better one, that doesn't usually gouge me.  It was NOT good enough   
   > for repairing band saw blades.  But there should be no flex in your   
   > carbide to steel connection.  If you want it you know how to reach me,   
   > to remind me of your address.  (If I can find it.)   
   >   
   > There are light fluxes and dark fluxes, and I think those with boron   
   > (black brazing flux) is best, but borax might be a poor man's   
   > alternative.  They use borax at forging temperatures afterall, (and   
   > for some heat treating operations) so it probably won't burn off.   
   >   
   > Some I recalled, some I got from an old This Old Tony Video, and some   
   > I double checked using Goggle's AI search function.   
   >   
   >   
   >   
   I wonder what makes the black flux black as both borax and boric acid   
   are white crystalline solids at room temperature, I have both. I have   
   had brazing flux for brass filler which was pink in the jar, worked fine   
   pretty colour. Boric acid AFAIK is what is used in gas fluxers often   
   used by those that produce fillet brazed frames and gives the flame a   
   green tinge, IIRC the fuel gas is bubbled through the boric acid   
   solution so some is entrained and gives a continuous shield with no   
   solid flux addition required in the joint. I tried a mix I found online   
   which called for them as part of a recipe for preventing/reducing   
   firescale on steel during heat treatment and it didn't seem to work very   
   well, subsequently I got some Condursal Z1100 and that seems to work   
   well, cost more but does what it says on the tin.   
      
   Some years ago a skilled blacksmith I know was in contact with some   
   smiths in the US and they raved about some miracle flux they could get   
   your side of the pond but the suppliers wouldn't ship it here. Pre 9/11   
   one of them travelled to the UK and brought some in his luggage and when   
   the guy I knew tried it he wondered what all the fuss was about as in   
   his experience it was no better than the borax he and others had been   
   using for hundreds or more years for forge welding.   
      
   I do know from experience that the silver solder flux I have for tool   
   tips and stainless works better for those materials than the standard   
   flux for steel/brass/copper/bronze etc on stainless.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)