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Silver soldering 19mm steel.

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Robin Graham24/01/2020 23:22:25
755 forum posts
186 photos

I want to attach a collar, if that's the word, towards the end of a 19mm steel bar. I thought I'd have a go at silver soldering (or should I say brazing?) with silver-flo 55. This was my setup:


There was another bit of my homemade (patent pending) firebrick over the top, removed for the photo.

This was on a sacrificial test piece - I wanted to see if I could get it hot enough. I couldn't.

The torch is one of the smaller ones from a Clarke set fed from a standard propane bottle.

My question is - if I can find one of the bigger torches that came with the set, or even buy something better, is this feasible or am I on a hiding to nothing and need to look at improving my welding?


Hopper24/01/2020 23:25:54
4780 forum posts
104 photos

Don't know about your particular type of propane torch but for jobs like that I have a propane torch with a nozzle over 1 inch diameter. Still takes a long time to get large jobs up to heat. The one in the pic looks too small to me, but hard to tell from a pic.

Paul Kemp25/01/2020 00:11:06
548 forum posts
18 photos

As Hopper, nozzle too small, look for the 1" plus one that came with the torch and screw the regulator in to get a decent flame. Looks like it took too long to get the job up to temp and your flux was burned / beads indicate temp not high enough probably the rod melted by the torch rather than by heat of the job so it didn't flow. Make sure your home made fire bricks are not absorbing heat but are reflecting it back to the job.

If you can find a commercial lagging company see if you can bag some off cuts of the white mineral high temp insulation mat (various trade names). You need a company that insulates steam pipes, exhaust pipes etc. Stuff comes on a roll in boxes about an inch thick, quite expensive to buy but on lagging jobs there are always trimmings of reasonable sizes. Price of a pint to the lads will get you plenty. Lasts well and it's really effective.


not done it yet25/01/2020 05:17:16
4891 forum posts
20 photos

Improve your welding!

JasonB25/01/2020 06:59:12
18649 forum posts
2049 photos
1 articles

Also looks like you have totally exhauste dthe flux or did not use any as there is no sign of it on the workpiece. You will need HT5 or Tenacity No5, big burner, 4bar regulator and be prepared to wait for it to warm up.

Don't know what your blocks are made from but I doubt they are reflecting much if any heat back into the job. You also have the air holes of the burner down inside the blocks which will mean they don't draw in plenty of fresh air and may even cause the burner to go out.

Edited By JasonB on 25/01/2020 07:31:23

CuP Alloys 125/01/2020 15:35:10
249 forum posts

Hi Robin,

In order to get you on your way as quickly and efficiently as possible, I would like to have a bit more background. It takes the guesswork out of it as there are a few answers that could help you, but I would rather give the help that WILL help.

Please send a pm with contact details. I will get back to you.



Robin Graham25/01/2020 23:55:29
755 forum posts
186 photos

Thanks. To clarify, this wasn't an attempt to do the job - I just wanted to see if I could get the work anywhere near temperature with setup in the photo using scrap of the same size. If I had, I'd have been encouraged to look around the dungeon for a bigger torch, but I couldn't get beyond dull red and wondered if it was worth pursuing this approach. I've done a fair bit of silver soldering, but on much smaller parts and didn't know if was feasible on this scale without a forced air or oxy torch. Sounds like it may be doable with a bigger torch though - nobody's said it can't be done.

The DIY firebricks are vermiculite with ciment fondu binder - not pretty but they get to an orange surface heat within a minute or two, and they're barely warm on the outside after twenty minutes. So I don't think they're soaking heat.

The blobs on the work are witnesses of failed welding attempts, not solder - I gave up and thought soldering might be less frustrating,

I need to work on welding! I can run a decent bead (stick welding) but tack welding seems harder, with stick anyway. However, since starting this thread I have come across a YouTube video showing how to do it by holding the business end of the electrode like a pen, rather than trying to control it from the handle. Looks good.

Even if this works, I'll still be interested in the silver soldering alternative - thanks for your kind offer of advice Keith, I'll PM you.


Robin Graham28/01/2020 00:59:11
755 forum posts
186 photos

Just to update - for anyone else having trouble tacking with a stick welder, the video I found is here.

It really made a massive difference, for me at least. I wouldn't have dared to try this, even if I'd thought of it, had I not seen the the video. I guess it might be risky with a basic buzz box, but my inverter welder seems to shut down the current if I get a stick, so no glowing red-hot rods. 90 amps with a 2.5mm rod, job done.

Bit of a drift from the topic, but it's my thread, so that's OK! Problem solved, but I'll continue with soldering, brazing, (or whatever it's called) experiments.


Nigel McBurney 128/01/2020 09:17:23
727 forum posts
3 photos

Wrong set air getting to burner,gas burner too small, work laid flat on brick does not heat up. So have one fire brick laid flat and another upright so it looks like an angleplate, a propane burner about 32 minimum diameter with high pressure regulator ,and prop the work so that its above the surface of the bottom flat brick, I use some bits of broken firebrick,if the work is flat on the brick it does not heat up easily ,a bit up in the air and the flame gets around the work. buy a good burner mine is a Calor I bought 50 years ago with a selection of burners,since then I bought a large dia Sievert abd made an adapter as the threads are different,mostly used for getting black iron to red heat for bending. Calor no longer make their own burners so Sievert is a good alternative. I have a sheet metal hearth with white firebricks which I bought from an autojumble, another source of fire brick is my local woodburner stove supplier,they cut the insulating "brick" from large sheets to replace the stove linings,when I needed some for my stove i scrounged some offcuts

CuP Alloys 128/01/2020 13:09:07
249 forum posts

Hi Robin

See personal message.



SillyOldDuffer28/01/2020 13:17:15
6192 forum posts
1345 photos
Posted by Robin Graham on 25/01/2020 23:55:29:


The DIY firebricks are vermiculite with ciment fondu binder - not pretty but they get to an orange surface heat within a minute or two, and they're barely warm on the outside after twenty minutes. So I don't think they're soaking heat.



I'm a little suspicious of the firebricks. While Vermiculite is a good insulator, I not sure Ciment Fondu is. It's a refractory cement, tough, strong and very temperature resistant. Could be your bricks are thermally only middling efficient. I use the soft white bricks made to line Pottery furnaces. Although mechanically weak, and unable to withstand the high temperatures Ciment Fondu is good for, they're excellent insulators. Under a direct flame the surface goes white hot almost instantly.


Robin Graham30/01/2020 01:51:43
755 forum posts
186 photos

Thanks for further replies.

Nigel - I shall take your suggestions on board and change the arrangement on my DIY hearth - I have big bags of vermiculite and ciment fondu, and it's a quick and easy way of making firebricks which (pace Dave) work.

Keith@CuP - many thanks for your comprehensive email. I much appreciate your detailed advice on the basis of which I have decided to buy a 7kW Sievert torch. As I said to you the Clarke set wasn't a good buy - it was cheap, but it doesn't work well - I never could get a stable flame on the biggest burner. You gets what you pay for! Excellent (potential) customer service*.

Dave - I would like you to upgrade my DIY bricks from 'middling' to 'good', but I wouldn't claim that they are 'excellent'. Perhaps we could compromise on 'middling good'? Three and a half stars stars perhaps? I'm pretty sure that's not the problem though - it's to do with the torch.


* Standard disclaimer - no affiliation with CuP, but impressed by CS - engaging with the problem rather than just boosting a particular product.

old Al30/01/2020 10:01:48
170 forum posts

Its nice to have CUP on our side in their ever helpful self.

so you need loads of heat from a reliable source, but what has not been mentioned is the need to use a flux that can last the distance. You didnt mention what flux you tried using. We all have easy flow 2 in our toolkits, but it probably doent last long enough for this job

Robin Graham02/02/2020 01:51:24
755 forum posts
186 photos

To draw a line under my initial question and replies, I now have a Sievert starter kit with the 7kW torch. Compared with the Clarke set it's night and day. I did have a bit of a brown trouser moment when the Sievert torch flashed back and impressively threatening yellow flames burst from the air intake holes, but that was operator error - I don't have any sort of pressure gauge on the downstream side of the regulator , and I think I was running it too low. Worked fine when I cranked the pressure up a bit.

Anyhow, although I've not yet attacked the job proper, tests on scrap make me confident that it will work with this torch - my immediate problem is solved.

Al - I didn't mention flux in my original post because I was taking it one step at a time and wondering if I would even be able to get the metal to soldering temperature without going to forced air or oxy-propane, which wouldn't be feasible for me. I now know that I can. I have HT5 flux.

Thanks to all for advice, Robin

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