Rob Roy staying.

[Barney66]

Rob Roy boiler, all OK so far; I've got the 1/8" holes drilled for the 16 rivet side stays each side, total of 32, in the firebox and the outer shell. The outer shell holes are slightly countersunk ready. 1/8" x 1" rivets used as stays are a nice fit. All ready to be soldered, domed heads on the inside. Foundation ring hasn't been soldered, I was going to do that after the staying. Can someone talk me through the stay soldering please? I have a cyclone burner, so presumably flux everything then using that burner to solder the 1/8" rivets (stays) inside the firebox, a row of 4 at a time, should be OK, applying 1.5mm silver solder to the stays/rivet heads? Then the next row of 4 stays and so on. Then having done the stays inside, pickle and then heat the outer shell and apply silver solder to the other end of the stays where they poke through the outer shell. All done. Then trim the stays to length. I have read many accounts of this process, many involving rings of 1mm silver solder threaded onto each stay, sometimes 2 rings; one presumably under the rivet/stay head, and the other one in the firebox/outer shell gap? Does this involve two heats, applying heat to the inside of the firebox to melt the first ring and again to the  outer shell to melt the second ring in the gap? Or in a simple small boiler like this can one dispense with the solder rings? Any help will be much appreciated. I've been staring at this boiler for weeks! Many thanks.

[uuu]

Steve and I did his boilers with just one heat-up for each side of the boiler - so inner and outer joints in one go. We used solder rings - it's a bit fiddly to get them threaded inside, but we managed it. Two rings for each stay, one between the plates to do the inner joint and another on the outside tail. As we poked each stay in its hole, having threaded the tricky ring on (with a dob of flux), we nipped it with some cutters, to deform the tail enough to stop it dropping back out. Inner rings have to be coaxed to sit down onto the inner plate with a spatula.

The problem with the stays, as with any silver soldering process, is to get all the parts up to temperature, so the solder penetrates properly. Going a bit too gingerly, doing little bits only, risks spoiling it. Heating inside only, or outside only, and/or some stays but not all of them, invites the shell to get hot, but the stays to conduct heat away and stay too cool.


I like the cyclone burner - it can swirl a flame around an enclosed space - and we tried to squirt a bit of heat into the gap between the plates. We packed insulation blocks around the unheated areas - and put a blanking plate over the ends of the tubes to avoid remelting previous joints.

I've seen several experienced people do without the rings. Just poke the joint with a stick of solder. But their experience allowed them to judge the temperature just right. Steve and I liked to have the solder resting in the joint and then watch it flash in. If only half of it melted, or it seemed reluctant, then keep heating. And we know how much solder has gone in each joint. Perhaps we'll become good enough to use the poke-with-stick method - it would be quicker then making all those rings!

Steve's done a tiny pot boiler on his own. But for a loco boiler, even a small one, it would really help to have a buddy. Again, the experienced builders can do it alone, but we like the comfort of a second pair of hands, and eyes.

Wilf

PS - we wound the rings around a stick in the lathe. Make a coil, then cut it up, then twist each ring flat with two pairs of pliers.

[Barney66]

Many thanks for your reply, much appreciated!
Moving forward then, with all the stay holes drilled and slightly countersunk, the stays, which are basically 1" long 1/8" copper snap-head rivets, will all be installed and fluxed, with the heads inside the firebox. Some small 18g steel plates planted to protect the ends of the boiler tubes etc. Silver solder rings would have been threaded onto each stay,  in the airgap, and bearing against the outside of the firebox wall from the rivet head. All fluxed up, and the cyclone burner heating the inside of the firebox and the rivet heads, the molten silver solder rings in the gap will then migrate and flash to the  hottest part which will be the junction between the underside of the rivet head and the firebox wall. I think I would be then tempted to wash and pickle, inspect, and  then re-apply the heat to the outside of the wrapper, all fluxed, and apply silver solder to the outer junction of the stay/wrapper. Not bother with the second solder ring? If i do bother where does the second ring go?
Presumably the rings should be 1.5mm silver solder? I have a couple of propane torches so heat shouldn't be a problem.

Many thanks.

[uuu]

The 1.5mm sounds a bit big for the rings, with your little stays. If it's what you've got, then it my well work OK. Quite a tight fit around the stays will help, at the cost of making the assembly fiddly. An alternative is little solder horseshoes - although the boiling flux can displace these, and it's hard to spot in between the plates.

A bright torch will help you look for the rings melting, and/or a tell tale appearance of solder around the rivet head.

If you're going to do inside and out separately, then I would still flux up the outside joints, to keep them clean during the first heat up - then reflux for the second. But this also gives you an option: Do the inside as you propose and if it all goes really well you could carry on and do the outside too. You'll have a lot of the background heating already applied. If you feel it's taken a bit too long and risks the outer flux becoming stale, then stop and clean up.

For the outside heating, you don't have the advantage of heating from underneath the joint and drawing the solder in. So you need to be sure to get the plate and stays properly hot. Having the tails sticking up helps, of course, as they will absorb heat into the joint.

Good luck!

Wilf