Am I doing this right? Brass construction.

MillenniumFalsehood · Post by **MillenniumFalsehood** » Thu Apr 20, 2006 5:48 pm

Okay, I have a small propane torch and some acid-core solder, which is about 1/8 inch thick. I have a frame made out of brass that I need connected by "welding", i.e. it can't be done with physical connectors.

The problem is that I can't get the solder to flow in the right places, is there a way to control this? This is my first brass project, and it will be load-bearing(about twenty pounds max). I am going to put braces in strategic areas, but I'd like to know it I'm doing this right.

I've seen people solder Eagles together and I think there's a good, fast technique to it, I just haven't found out yet what it is.

Btw, this may be a good sticky topic.

Kylwell · Post by **Kylwell** » Thu Apr 20, 2006 6:06 pm

IIRC correctly acid core solder is for pipes. Get some reg'lar stuff, thinner is better. The object is to heat the area up enough that the solder flows into the crack. This can be problematic with brass as it likes to conduct the heat away. Worse try 99.9% oxygen free copper, oof.

I usually run the soldering iron on the underside of the parts, touching the solder to the top. Things will sit for a bit then, wham, in it goes. The tricky part (to me) is figuring out an angle to hold things, which gets even more of an issue if the object(s) are pinned to a bench.

MillenniumFalsehood · Post by **MillenniumFalsehood** » Thu Apr 20, 2006 6:39 pm

So I don't want to hold it in a vise?

Okay, I have some lighter-duty stuff, but it has rosin in the center, and it won't let the solder stick for some reason.

Also, is it completely necessary to sand off or grind off all corrosion? Because I figured it would be a good idea, but it's difficult to get all of it off.

macfrank · Post by **macfrank** » Thu Apr 20, 2006 8:00 pm

Don't use an acid core flux.

Sand or clean the brass where you want the solder to stick.

Hold the brass with either an insulated clip or by supporting and blocking the bits with bricks or something non heat conductive.

heat the joint between the two brass parts then apply the solder. You want the brass connection, not the soldering iron directly, to melt the solder.

You may need a pretty hefty soldering iron. A 15W pencil iron may not be enough if the brass is thick.

Chacal · Post by **Chacal** » Fri Apr 21, 2006 1:36 pm

One trick I heard about is to use clay (real, wet dirt type clay, not plasticine, not Fimo or other bakeable clays) to hold the parts to be soldered in place. You make balls of clay and support the middle of the rods/tubes, leaving the point to be soldered free.

MillenniumFalsehood · Post by **MillenniumFalsehood** » Fri Apr 21, 2006 2:48 pm

The stock I'm using isn't that thick, maybe 0.015 thousands of an inch thick. So acid core is a no-no, right? Okay. Would I have to look for a core-less type of solder, or am I just using the rosin-core solder wrong?

Kylwell · Post by **Kylwell** » Fri Apr 21, 2006 2:54 pm

I use Kester .025 solder. The thicker stuff just doesn't work for me.

Chacal · Post by **Chacal** » Fri Apr 21, 2006 8:40 pm

MillenniumFalsehood wrote:The stock I'm using isn't that thick, maybe 0.015 thousands of an inch thick..

15 mil, to hold 20lb?

MillenniumFalsehood · Post by **MillenniumFalsehood** » Fri Apr 21, 2006 9:40 pm

Sorry, it's 15 mil., but it's a tube, so it has strength, and there will be cross-bracing to improve the strength. This frame will also be in the center of a battlemech leg, so it will also have the help of the outer shell too.

macfrank · Post by **macfrank** » Sat Apr 22, 2006 12:32 pm

20lbs seems like a lot of weight, especially if it's going to be held together by soldered joints. Can you notch the brass tubes at the joints, so you at least get some mechanical support from the brass?

MillenniumFalsehood · Post by **MillenniumFalsehood** » Sat Apr 22, 2006 2:26 pm

Well, the edges are pretty rough, would that count? I am using a hack-saw to cut them up, since they don't need to be pretty, just functional, so the edges are pretty rough to begin with. I could start notching them, though. I haven't gotten too far yet.

DX-SFX · Post by **DX-SFX** » Sun Apr 23, 2006 7:19 am

http://www.eagletransporter.com/forum/v ... c.php?t=60

Kylwell · Post by **Kylwell** » Sun Apr 23, 2006 10:37 am

MillenniumFalsehood wrote:Well, the edges are pretty rough, would that count? I am using a hack-saw to cut them up, since they don't need to be pretty, just functional, so the edges are pretty rough to begin with. I could start notching them, though. I haven't gotten too far yet.

The finer the edge the better the joint. Try taking a file to them.

Darth Humorous · Post by **Darth Humorous** » Sun Apr 23, 2006 10:57 am

Excellent Link. And yes, that is ACID flux. Rosin is too weak for anything but very fine work like electronics it was meant for. And yes, it is imperative that acid flux be cleaned from the parts after soldering.

Right on target except for one minor thing. The comment, "In practice though it takes more heat to melt a joint than it took to form it. That's because the solder has alloyed with the brass and it's now a tin/lead/brass (copper and zinc) alloy", is not quite accurate. The truth is, the solder and brass are not alloyed, but there is indeed a bond. The real reason for longer heating is that the soldered joint contains more mass than the original UNsoldered joint. And more mass to heat means more time to heat it. Also to some degree, depending on joint geometry for the soldered joint, more parts are now substantially connected, and the now bigger heat conducing pathway allows for that heat to more effectively soak up into the connected metal (where it is not wanted). So in effect, more (undesired) mass is coming into play through improved heat connectivity. Finally, there is the possibility of surface oxidation on the applied solder. This will impede the heat transfer through the joint as well. If possible, cleaning the soldered joint with a wire brush, sandpaper, etc., and coating it with flux prior to reheating will help.

I believe there is a brand of braided tin coated copper wire called "Solder Wick", or something like that, to help remove heated solder from a joint.

Mark

DX-SFX · Post by **DX-SFX** » Sun Jul 02, 2006 6:46 am

The comment, "In practice though it takes more heat to melt a joint than it took to form it. That's because the solder has alloyed with the brass and it's now a tin/lead/brass (copper and zinc) alloy", is not quite accurate. The truth is, the solder and brass are not alloyed, but there is indeed a bond. The real reason for longer heating is that the soldered joint contains more mass than the original UNsoldered joint.

No, I stand by what I said. There is the same mass of metal and solder before as there is after. There is the same conductivity of heat away from the joint before and after. You forget you have to heat the solder too in order to make the joint in the first place, not just the parts to be joined. Whether the heat to melt the solder comes from the flame or parts is not an issue since all the heat originates from the same source. The same mass is present and all parts must be above the melting point of the solder for the joint to form. The reason it takes more heat to remelt the joint is because the alloying of the solder with the substrate changes it's properties and raises it's melting point. I've highlighted the relevant bits:

http://homepage.ntlworld.com/sfx_films/joint.jpg

It's the alloying action that erodes the copper tips on electric soldering irons unless they're plated. The copper surface mixes with the solder so that when the solder is transfered to the joint, it takes tiny quantities of the copper tip with it. When you reload with fresh solder, it combines with the copper tip again and so the process is repeated.

Darth Humorous · Post by **Darth Humorous** » Sat Jul 08, 2006 12:25 am

DX-SFX wrote:No, I stand by what I said.

O.K.â€¦by all means, stand away. Perhaps the most pertinent part of your link is the sentence immediately following the section you highlighted. Most interesting since the distinction is made between two different chemistries and applying the same name of "alloying" to both. So "alloying" is the name that passes for your alluded form of molecular swapping these days, eh? I'm glad you put that there, because I thought you meant the original, longstanding definition of "alloy", which I know isn't the case here. Don't seem to recall the use of that term applied to this bonding chemistry in my metallurgy courses. The idea is fairly sound, but the terminology threw me. I'll buy the idea.

Also, I didn't forget anything in my previous post. I don't mean to suggest a violation of conservation of mass. It rather has to do with real world logistics of actually dealing with a now different structure (pre vs post soldered). And as far as conductivity goes, again it boils down to logistics. But yes, in effect, conductivity changes. Its significance depends on the actual conditions and geometry.

Oh yeah, in the case of the eroding copper tips, this also happens on externally heated irons, not just electric ones. To the best of my recollection, this is referred to as galvanic action. Or in the case of soldering, accellerated and aggravated galvanic action.

Mark

Kylwell · Post by **Kylwell** » Sat Jul 08, 2006 10:51 am

I beleive the term ya'll are looking for is 'tempered'.

DX-SFX · Post by **DX-SFX** » Sat Jul 08, 2006 3:48 pm

Obviously true alloying needs all the metals involved to be brought above their liquidus and mixed but the principle is similar at the contact surface.
The conductivity question depends entirely on how fast you can bring the local area of the joint up to temperature. That's OK for small joints but with much larger pieces you'll barely notice a difference between pre-solder and post-solder times. I learnt that from thirty years (is it really that long?) of actually doing it.