Problem with my silver soldering

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Hi,I have a problem with my silver soldering, and I don't know why. Whenever I silver solder solid pieces together, no problem, whenever I silver solder tubes together, no problem, whenever I try and solder a solid rod to a tube - problem !I often want to silver solder a brass rod of 6mm diametre to a tube of 19mm diametre and I always have a big problem, it's as though the heat is escaping somewhere because I stand there for what seems like ages and ages before the flux begins to heat up properly and then the silver solder doesn't really melt or flux that well, it is really difficult and the end result is always a little messy. I have tried filling the tube with solid brass rod so that it is like a solid piece but this does not work either, I just cannot sort out what the problem isI am using plenty of flux and the joint is always sound, the assembly simply will not heat up properly and I am using the same equipment and methods I use with the rest of my silver soldering which as I said is normally no problem at all. Does anyone have any ideas why this is happening and what I can doThanks for any feedbackflynnboy
Reply:Hard to say without actually being there but if I was to guess i'd say the solid rod is drawing the heat away from the joint. The rod, being a greater mass, is going to require more heat than a piece of tubing to get to the correct temperature. Not only that  it is going to hold the heat longer once it does get up to temp.Try firecting more of your heat toward the bar instead and just let the edges of the flame toouch the tube.All this being said if I understand the problem correctly.....Mike
Reply:Mrmikey is correct. The large difference in mass, especially density vs. surface area is what is goofing you up. Concentrate the heat on the solid rod first, maybe add a bit more heat to the solid itself, and then turn the heat back to the normal heat you use and hit the joint. That is always a challenging type of weld or braze. Good luck.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:What they said X2. They large difference in diameter is going to mess with you. solderin and brazing relies on a good mechanical connection in order to have a strong joint. Soldering more so than brazing. Soldering just doesn't fill gaps well. Not to say that the two tubes can't be stuck together with solder but it won't be very easy nor very strong.
Reply:More details would be useful: which solder and flux, what thickness is the tube's wall, what type of heat, how long are the parts, is the solder pre-placed, etc.
Reply:As with all soldering you have to keep touching the base metal until the wire actually melts when making contact.  Silver solder loves tight joints.. the strength on a one or two thou. gap is way over the strength of the steel.  You might even consider snipping off a small piece of wire and locating it at the joint then gently applying heat until it runs.  If the tube stands vertical on the end of the solid 19 mm piece then you could even locate the piece sitting inside the tube and just keep applying heat to the solid piece until the solder runs out of the butt joint and shows itself on the OD.
Reply:Thanks for all of the input, I have attached some pics so you can see what I'm up to.I am using silverflo 55 rod 630 - 650 degrees with easyflo 2 fluxI do actually target the rod with the torch but it doesn't really seem to help.Thanks againflynnboy Attached Images
Reply:What is that for?Yup
Reply:The joints look pretty good.  I think I am looking at one line where there is a failure to bond completely on the second picture?  In point of fact you are dealing with seven joints on that assembly if I take the two strips on the legs of the saddle into the count.  It is very easy to see the problem now ... as for a solution... I am not sure.  Purists in the religion of silver soldering might select two different temperature alloys and joint the small bars first to the shaft before joining the saddle saddle with a lower temp alloy.  From the look of the alignment complexity you must be using some sort of support or clamping affair to hold everything in place.    ( Lotech tips his hat to you)  Silver solder likes a surface contact connection so that capillary action can take place.  The small rods only make line contact.  This is just an observation, not a criticism.  I am guessing that you are getting an oxidized surface on the joint and that is why the line appears.  You mention you are using lots of flux.  I doubt this is the problem.  If all the parts are brass you could easily soft solder that with 50/50 and get enough strength  that the saddle would bend before you would have failure.  Last thing that comes to mind is that I don't think Easy Flo is the best for brass.   Have you looked at "The Brazing Book"  I believe it is still on line?
Reply:Yes you are using the wrong silver solder.  Silfos is popular for brasses.. never used it.   Also it looks like Easy Flo 35 is one choice.http://www.handyharmancanada.com/The...ents.htm#Index
Reply:Thanks again for all of the input.The long tube is 280mm x 0.5mm wall. This is first attached to the curved piece by a short tube of 7mm dia' by silver solder, you can see this in assembly4.jpg After the long tube is attached to the curve the 70mm x 6mm dia' rod is placed on the curved piece resting in position against the tube by its own weight. Flux is then applied and the piece soldered along the side meeting the tube and the side meeting the top of the curved piece. The two bars at the edges of the curved piece are attached before anything else. Voila.I don't really know the technical details of my flame save to say that it is a Bullfinch torch# 1472 - this has an internal dia' of 13mm and the gas is Propane. I use the highest setting on the regulator.I don't believe that the flux or the solder is my problem because I never have a problem with any of my other silver soldering, only this particular part of that assembly. I do eventually get the solder in but it is hard work and takes too long, leaves a messy fill and a lot of cleaning up afterwards. Something is stealing the heat and I've tried everything I can to stop that happening but I can't crack it.flynnboy
Reply:BTW  I don't think I can use a soft solder because the piece has to be chrome plated when it is finished and I don't think it will take to soft solder ?flynnboy