Soldering time.
Took me a little time to get all the pieces square to each other. I braided some wire as
Dennis showed in his Rudy Kouhoupt steam tractor thread. That's a good tip! In the past I've just
used straight single strands of tie wire for this kind of thing. Twisting a loop of wire into a braid
really helps the wire stay where you put it. Thanks, Dennis!
To start with the soldering, I did the top four corners, as the piece seemed happy to stay square while
sitting upright on it's feet. I'm not new at hard soldering, (silver brazing), but don't do it enough to be really
good at it. Still, I know how to make a decent joint. The four corners were pasted with a bit of flux,
and each corner got a small piece of 56% silver wire.
These are the hard solders I use. The 56% is BAg-7, and the 45% is BAg-5. If you are in the U.S., all
you need to know when you go to buy hard solder is the spec number. Ask for it by specification number,
and you will get the right stuff, no matter who makes it, whether it's from Harris, SRA, Eutectic, or
whom ever. It can say "Super Duper Easy Flow Extra Do-Da Day Solder" on the package, but if it has that
BAg-(X) spec on the pack, it will be the same as any other maker's Super Duper brand of solder that has
the same BAg-(X) spec.
The two solders I use are cadmium free.
The flux being used is Harris brand White Brazing Flux Paste. SRA also makes a white flux paste, and it works
the same as the Harris stuff. SRA calls their flux "601". There are other flux makers, but I can't remember
the names of them. Plumbers flux will not work for silver soldering. It burns up way before the solder
will melt.
To give an idea of how much solder is in an ounce, the thinner one in the pic has only had a few inches used
from it. It's .031" diameter and is what you get in an ounce. The thicker solder is .062", and has had a
good bit used from it. Probably about 1/2 ounce sitting there. I used about 6" in soldering up the firebox.
An ounce of .031" silver solder of most any type is around 20 feet long. An ounce of .062" silver wire has
a length of about five feet.
Regular hardware store type plumbers torches are used for the heating. I wasn't sure if these would get
hot enough for 1/8" steel on a piece this large, but they did okay. After the first few joints were done,
I substituted a bottle of MAPP gas for propane. It cut down the heating time noticeably.
The torch(s) you need depend on how large your work piece is, and the material it's made from. Steel is
not hard to keep at a soldering temperature. It holds heat pretty well. The thing is getting it up to
temp to begin with. The 1/8" sections being done here took a while to get up to soldering temperature, but
once one small area was to the point where solder started to flow, it was just a matter of chasing the joint
slowly with the torch flames and running the heat down the joint.
Copper and brass behave differently. They heat up fast, but the body of the work also wicks heat away at a
pretty fast rate. Ultimatley, the higest temperature your torch will produce is not so much the issue when
silver soldering. Even a tiny torch will make a 3000° flame, but it will be so small that it can't deal with
the convection that of the piece that pulls heat away from the joint. What you need is a large volume of
heat, rather than the peak temperature that would seem to make sense to us. A large soft flame will heat
a large area to a given temp and keep it there much better than a small intensely hot pinpoint flame.
Each corner was heated individually using one torch on the outside corner, and one torch flame playing
on the inside of the same corner. These were done with the 56% BAg-7 solder. The stuff I have is 1/16"
diameter, and each piece was sufficient to flow down the corner about ½". I used the 56% because it melts
down around 1150° f, which is about 200° less than the melting point of the 45% type. Even using 1/16"
diameter, it gets to flowing temp faster than the .031" diameter 45% that I have. The 56% costs
about $5 more per ounce than the 45%, but the lower melting temp is worth it. The two solders have a
similar strength, and both are suitable for copper, brass and other copper alloys, the various steels,
and other stuff I don't know about.
The bottom corners were done the same way, but the solder was put into the inside of the corner, since
I could get to that location with the torches easily. For these, I cut the pieces of solder about a
half inch long.
For each place you solder, as you heat the joint, the flux will start to bubble up, then the bubbles
will get dry and crusty looking before it goes liquid again. When it makes that crusty stuff, it often
pushes your piece of solder up a bit, raising it above the joint. Just poke it with a thin piece of wire
to put it back in place.
The reason the flux bubbles up is the water in it is boiling away. When the water has boiled away, it
is basically a mass of dry minerals and chemicals. This brings up a point that can be made here; If
you have paste flux that's been around a while, it will start to dry out, even though you keep the cap
on the jar. If it starts getting too thick and hard to brush on, you can add a little water to thin it
out enough to make it usable. That won't hurt it in any way. If you wait too long to re-moisten your
flux, it will eventually turn to a hard rock, and then you probably need to buy some new stuff.
When you see the flux go liquid, the heat is getting close. Watch your solder at that point. Shortly
before it starts to melt, it will start to get a shiny/wet look to it. Right after that, it will melt, and
sit in a puddle for a few seconds before it starts to flow. Keep your heat right on the joint 'til it flows.
If you are doing, say, a 1½" long joint, you would probably start heating at one end of the joint, and
when that end of your piece of solder starts to flow, move your heat along the joint slowly to get the
rest of the solder to follow suit.
If you have a gurt big torch, this will be easier, as the larger sections of the work piece will maintain
a flowing heat, and your solder will melt and get to flowing temperature all at once.
Once all the corners on top and bottom were soldered, I knew the piece wouldn't move and I got rid of the
wires. Then soldered down from the top about another inch and when the piece was cooled, mounted it on
the mill as in the pic above. The legs on the bottom were flat, but where the edges at the top met, it
was a little bumpy, so I took off .015" to make a nice flat place for the top plate.
To hold the top piece on for soldering, a rod is run through the arcs in the bottom, and a twisted wire loop
run up through the top hole.
Then a small rod is used to twist the wire loop until the top piece is tight against the base.
The piece of wire hooked to the right end of the rod is to keep it from un-winding.
This is where I'll leave off today. The flux is on the joint, a few pieces of solder sitting there
waiting for things to get hot.
Thanks for checking in.
Dean
