Silver soldering stainless steel

I have a need to make 12 stainless steel t-handles with the core stock about 14 mms diameter and the tommy bar itself 8 mms diameter. The core is 12mms long and the tommy bar is 60 mms long, so not a big item. This job has not gone particularly well so far, although Keith Hales book has given me some good pointers.

My queries are 1) Keith suggests a minimum gap for capilliary flow of 0.05 mms but I have no means of measuring such a gap accurately when the hole is only 8 mms diameter. Elsewhere Keith talks of a "Good rattling fit" which is probably common jargon in the UK but unknown to me in Australia. How do our members decide what is a suitable gap? Can someone explain what a "good rattling fit" means?

2) In theory I could use a high strength Loctite but I lack confidence in this because the job is for the filler caps of vintage motorcycles and will be exposed to rain and maybe petrol. If I did use a high strength locktite how tight should the parts be - drive tight, light tap or firm hand push? The material is 304 stainless. Regards, Chas

It might be helpful, Chas, if we could see a picture or two of your soldering set-up and results. Aside from the question of the gap, other questions arise: is your torch big enough, the joint clean and adequately fluxed? Are you directing the torch in the right places, for the right amount of time, with the torch the right distance from the work?

If it was me doing the job, I would simply drill through with an 8mm bit to get the required clearance, expecting this to be a good basis for a viable joint with an 8mm tommy bar.

Soldering parts together when one part is significantly fatter than the other is only really tricky if you heat the two parts unevenly, by which I mean you get the two parts at the site of the joint unequally hot. Naturally, if one part is fatter than the other, getting the parts evenly hot may mean letting the torch play more over one part than the other. The best guide to whether the two parts are being evenly heated is their colour, and the behaviour of both flux and solder as flow temperature is approached.

Edited By Bill Phinn on 30/09/2021 12:20:25

Hi Chas

A rattling fit is one where you can hold the 2 parts in your hands and feel them move them slightly when you apply a little pressure in each sideways direction. Think of a loose fit, if it were a shaft in a bearing it would rattle as the shaft turned. If your tommy bar is a full 8 mm diameter you might need to drill 8.2 or 8.3 mm to get a rattling fit.

Fits for loctite are usually, similarly, a little loose to allow the adhesive to flow around the joint. Then set the assembled job aside undisturbed for the adhesive to cure.

Keith is your man for silver soldering techniques.

You don't need any real precision on the job you describe so don't be afraid to leave the joints a little loose.

Rod

So photos of 'This job has not gone particularly well ' would help a lot.

Did the solder flow or did it remain lumpy?

Did the flux get into the joint and did it remain clear?

Any steel is slow to come up to temperature and it may be red on the outside but still too cold in the middle.

Loctite 603 is OK with oil and pretty strong.

You also don't say what solder and flux you have been using, stainless will require Tenacity No 5, Cup's HT5 or something similar as these fluxes are able to remove the chromium oxide that forms on the surface of the stainless when heated. Standard EF flux won't do that. Ample heat is also needed to get the part upto temp this means a suitable size burner probably 7Kw plus not a diy blowlamp regardless of the gas temp.

I would just tend to drill the hole and assuming the nominal 8mm stock is just a bit under be happy with that as a fit

Jason is right ! for stainless you need a high temp flux eg Tenacity 5 to remove the oxides formed with stainless and plenty of heat. A good rattleing fit is as it says loose enough to rattle, though personally I would have felt that was too loose for this job. A sliding fit with a bit extra slack. Good Luck, Noel.

Hi Chas,

See personal message.

Let's not complicate things unnecessarily.

Keith.

Hopefuly this intervention won't deprive the rest of us of hearing further about Chas' problem.

Agreed, I like hearing the responses as its all learning.

Hi all,

When I can appreciate what Chas is doing, why, how and with what, then I can offer sound practical advice to resolve the difficulties. In the meantime, I don't want to add to the confusion by introducing facts that are at variance with ill founded opinion.

I am confident that the answer is in my book.

It's not bedtime reading, but it's a good source of information to achieve good, strong brazed joints.

The usual disclaimer does not apply. 😃

Keith

Hi Chas

A special silver solder sticks are available especialy for stainless steel with a flux coating. Loads of info on You Tube or on a Google search for "Silver Solder Stainless Steel".

Another posting with unknown provenance.

52 years in the brazing/silver soldering brazing business, I have not come across a "special silver solder for stainless steel". I have come across alloys that are suitable for ferritic stainless steel in certain conditions.

What I have come across are common silver solders being used correctly and universally on austenitic stainless steel in a wider range of conditions.

Austenitic stainless steel is non-magnetic.

In my experience, "special silver solders" are often of unknown composition, at a premium price from red and yellow boxes. Is yours the one with the pink coating? Cheaper to buy the bare rod and flux!

Before buying it, ask yourself, "Do I really know what I'm buying?"

Any problems that Chas may have are extremely unlikely to be anything to do with the alloy being used.My earlier posting illustrated!

You pay your money and take your choice.

Keith

Edited By Keith Hale on 30/09/2021 20:40:37

Somehow I have just lost my long reply to all the good folks who replied to my post. Also no luck in getting photos onto the post - looks like I will have to look through old posts detailing how to add photos. Maybe I need to create an album.

I think my troubles are self-inflicted. I had some cadmium free 45% silver rod (BOC 45T) and some JM Easyflow flux and tried those. I could not get sufficient flow through the joint and I see now that the Easyflow flux is not adequate for this situation.

As Keith rightly says, all the answers are in his book, except that I was not sure about the fit required.

I think my rod will be OK for the job. I have some Tenacity No 5 and will try again after a good clean-up and re-tolerance.

I am using disposable cylinders of "MAP gas replacement" which seem well up to the job ( I seldom have need to silver solder so not worth investing in more expensive equipment). This is my first attempt at soldering stainless steel and screening the job with vermiculite blocks.

Interestingly a google search for Tenacity No 5 does not throw up any results but I can find results for other tenacity grades. Tenacity No 4 is available in Australia but apparently not No 5. Would Tenacity No 4 work or not for stainless?

Will try to send photos later. Chas

herewith photos to go with my previous posting

Leaving aside the clearly contentious question of which flux and solder to use, I wouldn't want to have to use that torch for that job. It's probably doable, but I wouldn't relish it.

As a couple of us have suggested, matching torch size to the size of the job is particularly critical for successful soldering. A good initial choice for this and bigger jobs would be something like a Sievert Pro 3486 torch handle with a 2941 burner. Kits containing these plus hose, neck tube and regulator are available (in the UK at least) for scarcely more money than the cost of that somewhat limiting Bernzomatic torch.

Hi Chas,

45T is not anything "special" but it will do the job you require.

Joint gap details and a method of attaining them are in the message.

Torch should be suitable but check in your book for the best way to heat the components to produce the strongest joint.

Regards

Keith

Keith I really do appreciate the time, patience and effort you put in helping people, including me, on the forum. Especially when my problems this time mostly come under the category of "When all else has failed,read the instructions".

Bill Phinn. As far as I can see with my inexperienced eye, the torch is adequate for this job but I have noted your input and if I'm still in trouble I will have to purchase the kit you recommend. When all else has failed.........!

Dave Halford. That is a good point you raise about the centre of the job being hot enough because stainless is a poor conductor of heat. I don't think it is the problem in this case but it's a point to consider on future jobs

Regards, Chas

You may be able to find Harris Stay-silv Black Flux down under which will work with stainless and any extended heating time due to the small torch

I believe that cadmium bearing 'Easy-flo No.2' equivalent solders are still marketed In Australia. From comments on another forum you need to source from Model Engineering suppliers, not 'Buntings'. This silver-solder composition, whilst being more expensive, may make your life a little easier with a lower melting-point and greater propensity to 'flow' than the 45% silver composition that you are currently using.

Regards,

Phil.

Hi Chas,

What are the fire bricks made from? The three look like house bricks.

I originally made the mistake of using bricks that line a house fire grate, they make a great job of robbing heat.

Vermiculite barby bricks are best, they actually insulate.