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chucketn
12-07-2012, 04:42 PM
I have a noob question on Silver soldering/brazing. I have only silver soldered 1 part in my life. I have a part that press fits together with finger pressure. It's a shaft for a crank, and the other part is a flange for the crank bearing. Is this type of fit 'loose' enough for silver solder to wick/wet between the parts?
Should I flux the mating surface of both parts before pressing together?

Chuck

Forestgnome
12-07-2012, 05:25 PM
Yes and yes.

lane
12-07-2012, 07:14 PM
Just to make sure the solder has a place to go .I like to take a needle file and file some small groves in the bore to make sure the solder can get in .If done right you cant see them later .

Black_Moons
12-07-2012, 07:40 PM
Yes and yes. Make sure to clean with wire brush and then solvents too, idealy. (Wire brush is likey to leave contaminates)

Evan
12-07-2012, 07:54 PM
Silver soldering is part of the brazing family of metal joining methods. Here are some high quality resources on this subject:

http://www.lucasmilhaupt.com/en-US/brazingfundamentals/properbrazingprocedure/

Register here for free and you may access the Brazing Handbook which covers every aspect of the field in great detail.

http://www.brazingbook.com/

chucketn
12-07-2012, 07:56 PM
Thanks for the references , Evan. I will study them.

Chuck

Stepside
12-07-2012, 07:59 PM
The parts need to be clean. This is not "solvent or soap clean but stainless steel brush clean or new abrasive paper clean. If you need to touch it, wear some disposable gloves. The clean is for the areas where you want the solder to flow. I use Yellow ochre where I don't want the solder. A good trick is to clean the solder and then place the end that you are going use in the flux until ready to use. Also a slightly carburizing flame is much better than an oxidizing flame.

chucketn
12-07-2012, 08:45 PM
Evan, the Lucas-Milhaupt ref is great. I went to the brazingbook.com sitr and registered, but when I clicked on the Book link, I get a blank page and now I can't get back to the origional link!

Chuck

Mcgyver
12-07-2012, 09:09 PM
no and yes.

silver solder needs a few thou clearance wick in. Do use lots of flux. If the parts require finger pressure there isn't enough clearance imo. If you need to press it in there is likely not .001" overall difference.... of course it really depends on what finger pressure means - why not measure them and report back the clearance?

SGW
12-07-2012, 09:18 PM
I think the required clearance depends on which silver alloy you're using. Some alloys flow easily, others build up fillets and are good at gap filling.

Mcgyver
12-07-2012, 09:49 PM
I think the required clearance depends on which silver alloy you're using. Some alloys flow easily, others build up fillets and are good at gap filling.

I believe you are right, but don't they all require at least a thou or two? If its a close a fit as it sounds like, cylindrical retaining compound might be a better idea

RussZHC
12-07-2012, 10:12 PM
http://www.harrisproductsgroup.com/en/Products/Alloys/Brazing/Phos-Copper/Stay-Silv-6.aspx

http://www.harrisproductsgroup.com/en/Products/Alloys/Brazing/Phos-Copper/Dynaflow.aspx

that's just a couple from Harris, "all" will have some spec that lists recommended clearance (or they should), depending on the braze material and materials being joined

Forestgnome
12-08-2012, 02:48 AM
no and yes.

silver solder needs a few thou clearance wick in. Do use lots of flux. If the parts require finger pressure there isn't enough clearance imo. If you need to press it in there is likely not .001" overall difference.... of course it really depends on what finger pressure means - why not measure them and report back the clearance?

True, but I ws thinking about the poster's application. Even if he had to tap it on with a hammer, it's not likely that there's not enough clearance for solder. For that tight of a clearance consistently around the circumference, and a light press fit, it would have to be a precision ground od mating with a precision honed id. Clearance is something to keep in mind, and the technical references regarding clearance is important. Also true that cleanliness is next to godliness when it comes to obtaining good wetting during soldering.

darryl
12-08-2012, 04:14 AM
How much strength is actually required in this part? I'm just thinking that you might get a strong enough bond without the solder having to flow through the gap, if you create a slight chamfer on both sides of the part before pressing it on. That way, even if solder doesn't flow between the parts, at least it will wick into a channel all around on both sides. Still though I think you'd be better off to machine about a thou or so off one or the other of the parts. The part would be a bit of a sloppy fit, but then you use one of the tricks to make it center well before soldering. One that I like is to use a very sharp cold chisel to make several indentations around the circumference of the male part. The female part could then be forced into place- ideally this would take more than finger pressure, but nothing that you'd need a press for. The remaining gap would be enough to allow solder and flux to wick in. You want the indentations in the same direction that you want the solder to flow.

From what I recall, 2 thou is a recommended minimum gap. Chances are that the best bond is going to be obtained when the solder can flow relatively quickly into the gap. It might fill a 1 thou gap, but take a bit longer. The longer you have the parts at soldering temperature, the greater is the liklihood of oxides forming and interfering with the bond.

My intro to silver soldering was with 'unknown' solder, something my dad had around for some reason, and a jar of unknown flux, just something in a jar with no label. I then started to learn about the various alloys and their properties, then I had to check to see what I could actually get locally. I tailored my prep to the particular alloy of solder that was available, which turned out to be Easy-Flow 45. I've had pretty good luck with that.

Another trick I learned was to heat both parts evenly so they more or less arrive at soldering temperature at the same time. If you're heating one part and hoping it heats the other, that doesn't work very well. Also, if there's any way you can heat from the side opposite to where the solder is applied, you are creating a temperature gradient in the parts. Once the opposite side is hot enough to melt solder, it will be drawn to the hotter side- provided you've got some flux there that will flow ahead of the solder.

Ed P
12-08-2012, 08:37 AM
Ok, now what about a torch? I've got a sizeable one that connects to my gas grill's propane tank. Is propane enough for small items?

Ed P

Mcgyver
12-08-2012, 09:34 AM
Ok, now what about a torch? I've got a sizeable one that connects to my gas grill's propane tank. Is propane enough for small items?

Ed P

yes, propane is more than hot enough. Easiest imo is with a corner made from three insulated fire bricks. In fact propane is preferred over oxy acetylene as the later is too hot and wrecks the flux....when O/A is handy is on larger pieces but you have to be careful to heat the joint indirectly...propane is more fool proof for a beginner and what i use 90% of the time. With propane, flux really well, place a few quite small pieces of SS at the joint and carefully warm things up, being careful not to blow away the small pieces. This imo is the best way to get a very neat joint without excess solder and runs. I use 1/16" diameter SS as its easily clipped into short lengths perfect for setting in the flux at the joint.

loose nut
12-08-2012, 08:07 PM
For Easyflow 45

.0015" is the minimum gap and still be able to get capillary action to draw the solder into the joint.

.003" is the ideal gap

anything over .005" will cause the strength to fall off. IE: the greater the gap the weaker the joint.

this may vary a small amount for different types of solder

chucketn
12-09-2012, 07:44 PM
I want to thank all who have commented and offered advise on the techniques of silver soldering/brazing. A lot of good info to think about and apply.
A little background on me. I have soldered for electronics for many years. I actually taught high reliability soldering for the USAF for many years. I have also done some plumbing soldering over the years using propane and mapp gas, even an old kerosene blowlamp. I have only silver soldered/brazed once, and can't find that part now! So, I am familiar with the process and what solder flow and wicking look like.
I have my Dad's Proto torch set, regulator and acetylene tank that I intend to use for silver soldering/brazing. It needs a new hose, as the original is looking dry rotted and I don't trust it. I'm looking for firebrick to make a hearth, and have found a local supplier for the solder and flux, and a replacement hose.
I have uploaded a photo of the parts I need to silver solder/braze.

http://i571.photobucket.com/albums/ss157/chucketn/DSCF1344.jpg

The part, shown assembled at the top, and the 3 components at the bottom, is a connecting rod for a model steam engine. The clevis on the right end does not get soldered. The flat part on the left gets soldered to the end of the rod in the position shown at the top. The rod part is run of the mill 3/16 CRS rod, not modified other than faced in the lathe and threaded for the clevis. The flat piece is 1/16 crs plate, drilled and tapped 2-56 on the outaide holes and drilled 3/16 in the center.
As made, the flat piece is a light press fit on the rod. I used a ball pien to tap the rod into the flat piece on the anvil part of my bench vise to get a flush fit. I can twist and pull the flat piece off the rod with my fingers. I used a 3/16 drill to make the mating hole. If I use a #12 drill the flat part is loose on the rod.
Hope this clears up your questions and gives you a mental picture of what I'm trying to do.

Chuck

darryl
12-09-2012, 08:07 PM
You could drill the hole in the flat piece slightly over, then put a series of dimple marks around it to shrink it enough that you can still get a press fit. It won't take much of a dimple to displace the metal at the edge of the hole by a few thou. For that part I'd probably use a very thin piece of silver solder, say 30 thou or so, and cut a length that would wrap about half way around the rod. Just lay that semi-circle of silver solder against the junction, with flux all around, and heat. Or cut two quarter circles of solder and lay them on opposite sides.

Forestgnome
12-10-2012, 10:12 AM
If you've done high-rel soldering then you don't deserve the "noob" moniker!

Toolguy
12-10-2012, 11:16 AM
You could cut some flats on the male part, 4 or 6 equally spaced, leaving a generous amount of the original round surface between flats. That would give alignment and positioning with the round surface and space for the silver solder to wick into the flats.

Evan
12-10-2012, 03:00 PM
No need to make the part a loose fit. Just flow a fillet of solder around the rod and the part. That will be more than strong enough to hold it. To prevent any chance of solder flowing into the holes use a graphite pencil to fill the holes with graphite and also pencil mark the area around the ends. That will repel the solder in that area.

Use some flat solder and cut a piece just long enough to wrap around the shaft as a ring so it also contacts the plate as well as possible, embedded in flux. Heat by aiming the torch above the solder on the shaft but not to the point of melting. Then move the torch to the center of the bottom of the shaft and plate.

If you like you can also champher the end of the shaft slightly and solder the bottom side too. The solder will fill the groove after you file off the excess.

chucketn
12-11-2012, 09:12 AM
During my research for my silver soldering project, I cam across the .pdf linked below. It has good info including pictures of a reducing flame. I had run across several references to a reducing flame but this is the first illustration I've found.

www.richard-whitehouse.co.uk/Soldering%20notes.pdf

I also found firebrick at Lowe's.

Chuck

Evan
12-11-2012, 03:13 PM
This thread has got me thinking about my first ever silver soldering project. That was a while ago when I went to the California College of Arts and Crafts in Berkeley. I took a jewelry making course which I very much enjoyed. All the equipment available and a very good instructor. I still have the very first item I made. Everything else was given away, usually to a girlfriend.

This is it. It is a simple belt buckle made with a nickle silver back, brass random outliner and silver square drawn wire that I drew myself. It is silver soldered together with progressively lower melting point solders to avoid dislodging the earlier soldered pieces. There are two on the back that form the belt clasp. The parts were held in place with coat hanger wire bent to form a simple spring clamp. That keeps the pressure on the piece as the solder melts and the piece then closes on the work. The spring doesn't have much force so it avoids squeezing out the solder too much.

I made this in about 1967. That was the "Summer of Love" in the Bay Area. http://ixian.ca/pics9/biggrin.gif

http://ixian.ca/pics10/buckle.jpg

Evan
12-11-2012, 03:26 PM
That PDF is pretty good except for one point. As you are using acetylene the hottest portion of the flame is at the tip of the inner cone. More important is that the most heat is also at the tip of the inner cone. With propane the highest temperature is at the tip of the cone but the most heat is at the end of the flame. Propane breaks down to a secondary combustible molecule and it is the secondary combustion in the outer flame that produces about 2/3rds of the heat. The difference when heating something is very considerable. Most people hold a propane torch too close to the work.

joe51
12-15-2012, 12:38 AM
A little background on me. I have soldered for electronics for many years. I actually taught high reliability soldering for the USAF for many years. Chuck


Chuck, Where did you teach at? I took that class at Peterson Field back in 1974.

chucketn
12-15-2012, 06:40 AM
Joe, I was in FTD513 at Mtn Home AFB, Idaho for several years. It's all gone now. I visited in September and you wouldn't know the place...

Chuck

beanbag
12-15-2012, 09:57 AM
That PDF is pretty good except for one point. As you are using acetylene the hottest portion of the flame is at the tip of the inner cone. More important is that the most heat is also at the tip of the inner cone.

Interesting point. But isn't heat, once created chemically, also conserved? Why would the heat be lower a little bit further out from the tip of the cone? Where does the lost heat go?

The first time I did silver soldering was a few months ago. The tip was such that to get a neutral flame, the inner cone was really small, and barely sticking out. (I think the tip was called 0 or 00) If I held the torch too close to the work, occasionally the flame would blow out with a loud pop.