silver soldering Gerry's beam engine crankshaft

[blackfoxsteam]

From previous posts it appears silver soldering steel can be difficult if not done correctly. To solder the throws tothe crankshaft I have only a small propane torch that floods out when inverted, some old low temp silver solder with acid flux, and a few steel pieces to learn with. Advice? I see large propane burners for weeds, MAPP units, etc. Do I need oxy-acetelene rig? How hot and how long?

 

[Ryker Carruthers]

I use a plain acetylene torch for steel brazing and all other brazing. My favorite steel brazing rod is older than I am :big:

 

[kevincoxshall]

Hi
do you have a hearth? some firebricks will make all the difference.

have you also considered locktite, I made a crank shaft secured with locktite on a low powered hot air engine.

Kevin

 

[gbritnell]

From your post you say that you have some low temperature silver solder with acid flux. I suspect it's not silver braze but something that is called silver solder but is lead based. If this is the case it's not satisfactory for brazing steel.
I silver solder/braze all the time with a propane torch. I use the round concentrated tip and you're right if you invert it it will flood out but it's not necessary to invert it.
There are different methods for assembling multi-piece cranks, pressed together, lightly pressed with Loctite and silver brazed. Each method has it's own skills. I normally silver braze but the final choice is yours.
gbritnell

 

[geoff]

Hi
If your not sure about soldering just loctite it and mabe pin it as well with 1/16" rod as i have, it can look good.
Geoff

 

[Runner]

Yes I agree that silver soldering steel is very difficult, whereas I am able to silver solder non ferrous metals quite well I eventually gave up in trying to silver solder the steel crankshaft for my twin steam engine. The problems I had was that using a large propane torch that the steel was red hot before the silver solder attempted to flow and as it was the silver solder was deposited on areas that I didn't want it to occur, namely on places where the bearings were positioned. As it turned out there was more silver solder in the wrong places than it between the crank and journals. Removing the silver solder from the big ends was almost impossible at the skill level I am at. The steel had become blackened all over due to too much heat and was very difficult to clean to anything near the finish that I had prior to attempting silver soldering. I eventually binned that attempt and remade it using Loctite, its much easier to control where it goes and no clean up afterwards is necessary.

Having said that I recently viewed a post in WIP where a member made a crankshaft using silver solder and the photos showed that the changes to the steel due to heating was kept very local to the journals indicating that the heating source was very concentrated and very hot, my guess he used oxyacetylene torch. He even had a piece of blue plastic wrapped around one end of the crankshaft which was unaffected during silver solder.

If your bent on silver soldering I would recommend a small MAPP torch if oxyacetylene is not available.

Brian

PS see http://www.homemodelenginemachinist.com/index.php?topic=18958.0

 

[ShedBoy]

I used to hate the idea of solder going where it was not wanted until I tried correction fluid. It does work, don't know why but it does, it is like the solder is scared of it. Paint a line where you want it to stop and then flux, drop in the solder and add heat. Best trick for silver soldering.

Brock

 

[blackfoxsteam]

Suggestion of Loctite and pinning sounds good. What color Loctite and how are the parts pinned?

 

[Blogwitch]

With a normal silver solder and flux, if your steel parts are starting to go red, you've overcooked it, you may as well give up.

I keep stressing for small jobs such as this, you should use PALLIONS, small or even tiny bits of solder, placed around the joint, held in place by the wet flux, just enough to fill the 0.002" gap that must be left for the solder to penetrate into the joint, do NOT feed the rod into the joint, you will end up with it everywhere. It costs too much to waste.

You need to buy a GOOD stainless steel flux, equal to the TENACITY 5 we use here in the UK. Normal borax types just won't cut it, they can't take the heat and very soon stop working, well before you get to a temp that your silver solder will flow correctly.


John

 

[picclock]

@blackfoxsteam

2nd Bogstandard's post. Silver soldering is an excellent way to join metals if you follow a few rules. Use furnace bricks to reflect the heat to ensure no cold spots.

To prevent the braze running use tippex or just pencil, which seems to work well. To remove the flux dunk in cold water once the joint has cooled to 1-200C. Remove the oxides caused by heat with a citric acid pickle.

Sounds like a lot but its a very useful skill. I only use a Propane torch because when combined with the heat reflective bricks its easy to get to brazing temperatures and well above.

Good Luck

picclock

 

[Mosey]

I have been told that Whiteout or liquid paper does stop the solder flow, but is toxic when heated!?

 

[picclock]

@Mosey

It does work. It also probably produces toxic gas, but I doubt very much you would be near enough to be affected. An ordinary pencil works just as well if your worried, although it will wipe off with your fingers. Just apply it before the pallions/flux.

Best Regards

picclock

 

[Ken I]

Here's my crank for Gerry's Beam Engine - I did silver solder (silver braze) it using a propane torch and firebricks.
http://www.homemodelenginemachinist.com/index.php?topic=11452.msg131054#msg131054

But I left on material for clean-up - If you don't want to go that route use taper pins & Locktite. Actually given the performance of the engine I'm pretty sure just locktite on its own would be sufficient but you would need to jig it to get everything aligned while it cures.

Ken

 

[abby]

I use straight forward easyflo flux for silver soldering steel , mixed with a drop of water and applied before heating , I have never had any problem.
The steel needs to be very clean and free from grease.
I normally place a small piece of solder in position after heating enough to drive off the water , then heat with the propane torch until the solder runs , generally a dull red heat.
I have never had much success with the pencil or tipex trick but I have a quantity of graphite suspension used for lubricating high temperature valves.
I apply this with a small paint brush around the joint area and allow to dry for a few minutes.

These are ball bearing axle boxes for a locomotive I am building , threaded 7 BA.

The parts on the left had no graphite !
You can see the difference.​

Dan.

 

[Mosey]

My neighbor is a large custom metal-fabricating shop, who nicely gave me several small refractory blocks for doing my silver soldering. They have a scooped out cavity just right for my exhaust pipe soldering. (funny, he can't solder worth a damn, but he sure can punch, bend and weld, etc.) Nice, huh!