Brazing Question

[Arnak]

Hi,

I plan to do some brazing but when I check the how to manuals they say that there should be a small gap to let the brazing material flow through.

However, if I clamp the pieces together then there will not be a gap, so how crucial is it to have a gap?

Arnak

[havoc]

There are "gaps" and then there are "gaps". Trying to braze a lapped joint won't work because the parts fit together too well in order for solder to penetrate. If you make your pieces with "normal" work methods (filing, milling turning) then the surface roughness will be fine to let solder flow into the joint. Certainly if the production marks go into the joint. Then if you do not clamp too hard it will work. If in doubt, place a few light centerpoints will keep the gap open enough. (don't overdo the centerpoints, copper is very soft)

[Arnak]

Hi Havoc,

Brilliant idea regarding the center pops, I should have thought of that!

Thanks very much.

Arnak

[alanstepney]

Silver solder varies in its gap-filling ability.
Look up "johnson Mathey metal joining" where they show the differences between various grades, plus lots of other useul information.

With a grade that needs a wider gap, pieces of rusty feeler gauges are ideal.
Now you know why you kept that rusty set of feelers, instead of throwing them away!

[havoc]

It isn't my idea: "Soldering and Brazing" by Tubal Cain in the workshop practice series p95 and following.

[GWRdriver]

Arnak,
You don't mention what you are soldering, but no matter . . . I do copper boilers, quite often for others, and over time I've learned to be rather ruthless will the file in creating chamfers, channels, passages, and relief of all kinds in joints and flanges, minding where the solder needs to go and where the solder will make fillets. I've found this helps a great deal with solder distibution when one cold joint can ruin my day and in the grand scheme of things causes no harm.

[Shawki Shlemon]

I have read many boiler plans where they say ream the hole for bushes stays etc.. ,to me this is nothing but somebody wants me or others to fail . Gaps are essential , the solder must go somewhere .Like you GWRdriver I built a lot of boilers and like you I am ruthless with joints of all kinds for gaps .( gaps are my friends ). Arnak what sort of joint you are soldering but if it is simple lap joint ,flux the joint well, arrange it as you want it then place a weight (not very heavy ) of a rusty piece of metal on the joint to keep it there. Why rusty ,so that if by accident you touch it with solder it will not stick .If you tell us what you are doing may be we can come up with better ideas . Good luck .

[havoc]

I'm not a supporter of filed channels, chamfers etc. There has to be a gap, but it has to be controlled. I have seen boilers where they relied on filed channels that were a big failure. Too large a channel and not enough gap between the pieces: leaks both at the channels and at the circumference. Tubal Cain with his "engineerd/machined gaps" is correct: design your joint and gap as it should be.

[abby]

Do you mean brazing or hard soldering ? gaps are bad ! J&M claim that a 1" silver-steel bar forced into a 1" reamed hole will show penetration when silver-soldered with easyflo , I don't think brazing is as common today as a few years ago and is mostly for joining steel parts , copper braze will penetrate very tight joints , When sifbronze brazing it is the fillet that provides the joint strength and a good t-jointed tube when subjected to tensile test will split at the tube before the braze. It is bad to overheat during brazing as the braze alloy can infiltrate steel and cause weakness which can result in premature stress cracking.

[GWRdriver]

gaps are bad!

In building many boilers that has not been my experience. Perhaps I should explain that the "gaps" I make to are between .003" and .008" wide and are intended as solder conduits to insure that a supply of solder finds its way to points where it can flash into the joint from the edges which can't be reached with the solder stick. I also find that silver solder, in a properly cleaned and fluxed joint, will flash easily into seams which appear to be dead flush to the unaided eye.

I'm sure Tom Walshaw's technique is above reproach but at the moment I can think of only one economical way, time-wise, to "engineer" solder clearance throughout a boiler and have it stay that way for the duration . . . . install .005" silver solder ribbon in the joints as you go.

Can we also please add the word silver to brazing, if what you mean is silver soldering? The word brazing used alone implies the use of brass welding rod which should not be used in any part of a boiler.

[Arnak]

Hi Folks,

No, I do mean brazing, it's not on a boiler!

I am joining the cowcatcher for a Virginia, as I am making it out of pieces not from a casting so it is made up of small steel pieces.

A total of 20, ouch...

So I was planing to clamp parts together then braze using one of those gas / oxy sets, the small disposable canister type.

I think the tip of lightly center popping should hold the main structure slightly apart when brazing.

I will check out the book mentioned, thanks for that info.

Arnak

[GWRdriver]

Arnak,
Oddly enough I did just exactly such a cowcatcher many years ago using BMS & silver solder and it worked out very well. It's been long enough now though that I can't remember how I jigged it together. As likely as not it was probably self-jigging, parts fitted in such a way that it hung together on its own. This was fo a 7.5"ga loco and the frame was 1/8" x 1/2" BMS flats and the other thingies (their proper name eludes me at the moment) were simply 3/16" BMS rounds with ends bent and inserted into drilled holes in the frame.

Your Virginia would pre-date this era by several decades but in later years typical US practice was to use crapped-out boiler flue tubes which were in plentiful supply. Their ends were flattened and suitably bent and they were then rivetted to the pilot (cowcatcher) frame. When a pilot got pranged, by a cow or something, replacement tubes could be quickly and cheaply installed.

[havoc]

Brazing: originally used for joining metals using brass spelter these days also used for hard soldering and silver soldering
Hard soldering: used to indicate joining metals below their melting temperature but using temperatures igh above the typical lead-tin solders mostly used for silver soldering
Silver soldering: joining metals below their melting point with a filler alloy containing an amount of silver

There is also a type of soft solder containing 2% of silver but that is still a soft solder

Gaps are essential! All solders have a minimal and maximal gap defined. Go below it and penetration can be a problem, go above it and the gap might not be filled. Outside the optimal gap, the joint is always weaker.

[Shawki Shlemon]

Gaps are essential! All solders have a minimal and maximal gap defined. Go below it and penetration can be a problem, go above it and the gap might not be filled. Outside the optimal gap, the joint is always weaker.

[/quote]

I fully agree with Havoc , when we are talking about gaps we mean the parts are not tight together . The other thing I would like to mention is if one is silver soldering two different materials ,one has to judge what will happen when heated , will the gap increase or decrease,this will affect the penetration of the solder .The type of silver solder has an effect too for example 45% silver solder will flow better and at lower temperature than 30% silver solder . This has been my experience but I stand corrected . Like everything else silver soldering is an acquired skill by practicing , Experience = mistakes + bad jobs + questions + frustration + redoing the job etc..

[GWRdriver]

shawki said:

,one has to judge what will happen when heated , will the gap increase or decrease

Precisely.

[chris vine]

Hi,

I love using a silver solder called silverflo 55. It is lovely stuff and flows like water. I think it would flow through an interference fit. (I must try the experiment sometime...)

The only disadvantage compared to easyflow 2? is that it is a slightly higher melting point and if soldering brass, you are rather near the brass melting. Even if you are careful the brass can be a bit dissolved near the joint, leaving a slight under cut.

Also silverflo 55 is cadmium free.

Chris.

[Arnak]

Hi,

Thanks again for the info.

I did see some pictures of an early type American Loco, as you mention they seem to have used rather rough metal and bolted them through the catcher.

I suppose, if it works don't knock it. )

I have milled out the top off the frame to notch the bars in and fixed the rest of the frame together so it should hold OK for brazing.
Once the brazing kit arrives I'll find out.

Thanks again for all the replies.

Arnak