5" gauge Britannia (a builder's diary)

[springcrocus]

The backhead plate has been made in similar fashion to all the other plates and not worth repeating here. It has already been seen in the trial assembly of the outer firebox. Although it will be one of the last items to solder in place, I have been preparing the holes for the bushes as these need to be machined rather than just drilled.



As can be seen, the lower gauge glass bushes are set at about twenty degrees on the angled face. A 7/16" slot drill would have done the job but, not having one, I chose to bore them to size instead. A 10mm slot drill was used as pilot. I also drilled and tapped the four holes for the longitudinal stays.



To assist with getting the bushes in the correct place, I made a jig from an offcut of copper, drilled 1/4" clearance holes at the bush centres and drilled and tapped three M5 holes to take some stand-off screws. I also made some bronze plugs to go through the plate and screw into the bushes and these will be retained as blanking plugs for use at pressure-test time.



M5 cap screws will act as adjustable spacers to get the position of the bushes correct. They need to be level to ensure that no undue pressure is exerted on the gauge glasses.



These will be soldered into place just prior to final fitting of the backhead and I've still got the lower clack bushes to drill out first.

Steve

[Deleted]

Nicely planned out sir....

Pete

[JonL]

I like that.

[springcrocus]

OK, those of you who are experienced boiler makers and silver-solderers look away now. One of our members has asked if I could write a full step-by-step description of one of our boiler sessions. It's a bit long-winded, I'm afraid.

Today, we soldered the outer wrapper to the barrel and throatplate assembly, the preparation of which I covered a couple of posts back. First, this is the kit that we used to do the work. I have two 13Kg propane bottles and we have two Sievert torches, both with 4 bar regulators and blowback valves fitted. The two main nozzles used were the Sievert 2943 and, later, the Sievert 3526 cyclone burner.



We have tried using the larger 2944 nozzles but found that it gets uncomfortably hot working in the area. I suspect that the copper cannot absorb the amount of heat that is being delivered quickly enough so a lot of it reflects back and cooks the operator.

The solder we used was 55% silver solder in 1.5mm rods from Brazetec and the flux used was Brazetec universal pre-mixed paste. I find that this flux has a nice, sticky constituency and is easy to apply with an artist's small paintbrush. One of it's greatest advantages is that it stays clear, even after cooking, and doesn't go glass-hard as it cools and rinses off very easily in cold water. It is boron-based like most high-temperature fluxes and is good for up to 900 degrees C.



All our cook-ups are done in/on a hearth built up from a couple of celcon blocks sitting on a fireproof mat on a workmate. Walls are created to suit the job in hand and other bits of blocks used to fill spaces in and around the workpiece.



To start, we dismantled the assembly and gave a quick rub with some wire wool to the surfaces that were to be soldered and a wipe over with a cloth. It was still clean from the session in the pickle last week and didn't require any more than this. A small amount of flux was painted around the inside edge of the wrapper.



Flux was also painted on the flange of the throatplate and over all the nearby solder joints, including both inside and outside of the throatplate-to-barrel solderwork.



The two parts were brought back together, a small dab of flux was added to each screw before fitting and screwed up touch-tight. Clamps are used at the base, rather than screws, because I don't want anything interfering with the foundation ring.

Solder was cut to size and bent to shape to rest on the edge of the flange all the way round the inside. This took quite a while to get it all sitting nicely but it's worth the effort to ensure it doesn't fall off during the heat-up. There are four or five separate pieces of solder here.



More flux was smeared over the solder and the assembly carried through and stood up on the hearth. Blocks were stood all round to encase the barrel and a further one (not in the picture) sat on top to stop the heat wasting away out the top.



Using both torches with a low-power flame, gentle heat was applied evenly all round to the underside of the throatplate until the water had boiled off from the flux. In the past, we've put the heat in too quickly and the rapid boiling has dislodged the solder. Once any bubbling had ceased, we turned up the power and rapidly got the assembly up to just before dull red. At this point, we concentrated the heat near the right-hand clamp and waited until we saw the solder melt, then slowly moved the heat around the underside chasing the solder. As it melted, it was easy to see when to move the torches along and work our way around the throatplate to the left-hand clamp. This picture was taken about thirty seconds after removing the heat.



A few minutes later, we removed the blocks from around the assembly and left it to cool naturally until it could be moved by bare hands. After a gentle scrub in the rinse tank, it was moved to the pickle tank and left whilst we had lunch.

Back on the bench, we checked the screws to see if they had been soldered but half came out easily and the other half with a small amount of effort. Each of the holes was retapped, the screws given a quick pickle, flux brushed into each hole and the screws put back in. This time, a horse shoe of solder was placed on each screw head, nipped on, everything completely refluxed again and the whole lot carried back to the hearth. I changed my burner nozzle for the cyclone burner and away we went again, my colleague heating just below the throat plate and me heating the flange of the throatplate inside the firebox. Once up to temperature, heat was concentrated on each screw in turn until melting had occured.



The cyclone burner was needed inside the firebox because a normal burner quickly starves itself of the available air and goes out whereas a cyclone burner gets it's air from much further back and stays alight in the confined space.

After a final wash-off and a good long soak in the pickle, these three pictures show the results. The first one shows that all the solder has melted and flowed down into the joint.



The second one shows that the solder has flowed right through the joint...



... and the last shows the screws satisfactorily sealed.



Now it is time to start bringing the two sub-assemblies together. More next week.

Steve

[timo]

Steve,

That is a really useful post. Great work.

Thanks.

Tim

[delaplume]

Exactly what I had in mind earlier on-----Well done Steve ( and friend !!)

[jon38r80]

Realy clear and not at all long winded. Helpfull to those like me that dont like silver soldering.

[JonL]

Thank you, this is ideal for me.

[twombo]

S. The extra time put into Your Forming Blocks, Or “Bucks”, seem to help you Turn out really fine components. The process of Documenting is, And, Has been, An Special interest of mine For many years. I really enjoy watching this ‘Baby’ being born! Just the right number of, well chosen, words! thanks!

On this iPad, it really ‘pops’ for me! Your camera work shows the really “fair” surfaces you have created! Thanks for the Great notes on torch Sizes and usages. Kind of a Dance for the team. isn’t it?

Great things headed our way. The foretaste of the crown stay and shell arrangement you have given us has helped clarify my thoughts on moving forward!
Forest fire season, and Solar power upgrades have kept me out of the workshop for weeks! Keep up the great work!

Cheers!
Mick

[springcrocus]

Thank you, gentlemen, for your comments. I must admit, I was expecting Grandma to make an appearance with her basket of eggs but she appears to be having a day off. I hope some of the reluctant boiler makers here might now be willing to have a go, knowing that we can always go back for another bite of the cherry if the first attempt is unsuccessful.

Three or four more soldering sessions should see this boiler complete. Win or lose, I'm having a wonderful journey. Again, thanks for your support.

Regards to all, Steve

[kipford]

Steve
Wonderful build log, gives me some hope for when I get to mine. Where did you get your Brazetec rods from? I am interested in how they compare in price to other suppliers, but can only seem to find kits (10 rods plus flux) on line. Also I think earlier you stated you were using Citric Acid as the pickle, could you confirm please.
Regards
Dave

[David]

Really nice work.

You must have done a great good job on your boiler plates and their fit if you only need 1.6mm wire put along the joint and it fills things satisfactorily!

I had some pretty big gaps in places and not only did much 55% stuff disappear inside but 15% had to be used as caulking.

[silverfox]

Excellent

Really sums everything up easily

Looking forward to next instalment

Ron

[JonL]

I consider the whole process very intimidating. This sort of thread is a goldmine.

[springcrocus]

One thing that has been noticeable is that the tubes are very soft and have slowly bunched together near the base due to handling. Now that I'm preparing to bring the two sub-assemblies together, I need to get the tubes back to their proper position and have made another front plate from the previously discarded outer wrapper. I have made the tube holes 1/32" larger than the tubes to prevent jamming and made the O/D a rattle fit in the barrel.



I couldn't use the proper front plate because the holes are a bare half-inch and the tube-ends skimmed down by five thou to ensure the frontplate stays put during soldering. The new plate was slowly worked down the length of the tubes although I didn't try and force it the last couple of inches. As the plate went down, the tops splayed out fan-like and were squeezed back to position by hand.

The new plate also protects the tubes while I get on with positioning the two parts prior to joining. The four screws are to withdraw the plate just prior to fitting the proper one at soldering time.



The first job was to get the position of the firebox correct with respect to the front throat plate and get the girders in the middle of the crown. A piece of 3/8" square mild steel was cut and used to set the distance for the front part of the foundation ring, the clamps being used to get the softer copper pulled into place.



It was now possible to stand the boiler upright on its nose and the centrelines of the fixing screws were scribed on the crown. The position of each screw was centre-popped on the line and the inner section was then teased over to the central position and a G-clamp use to hold it in place.



Using a pistol drill and hand drill the twelve 2BA holes were drilled and tapped in similar fashion to the outer wrapper fixings and steel screws used temporarily to hold things together.



With the screws holding the two sub-assemblies firmly together, a start was made on the foundation ring and the first section of 3/8" square copper bar cut to length and shaped to fit nicely into the bends of the flanges. This is sprung into place at the moment but will be held with a couple of rivets later.



Getting there.

Steve

[Deleted]

Your project loks interesting. For it you need to have good calculator. I prefer to use calculator for calculating taxes or other things durinh my work. I am an engineer. So I have special reliable scientific calculator - HP 35s Engineering Scientific Calculator which I bought long time ago. Plus review

[JonL]

Anyone else beginning to suspect Kelly is a Bot?

[springcrocus]

The next parts made were the side sections of the foundation ring, cut to length level with the end of the firebox backplate. I've had the thin the front section of these a little to compensate for the firebox being about 1/32" over drawing size. Again, the clamps are used to straighten the sides.



The backhead needed the firehole cut out and for this I set the backhead in place and scribed round the inside of the firehole ring from inside the firebox. A felt-tip pen was used to ink a line about 1/16" all round and the hole cut and filed until the ink had gone.



Then it was slowly dressed with sanding drums until a snug fit was obtained, probably taking me about a half hour to do this. I don't want to be filling large holes here, particularly.



With the backhead clamped in place, the firebox backplate was eased back with a hide mallet to bring the firehole slightly forward for a flat fit. I felt this was preferable to bending the backhead in slightly. I also scribed the front edges of the backhead flanges onto the outer wrapper.



With this all done, it was time to make the backhead a snug fit to the outer wrapper and the whole lot was stripped back and the backhead set in place without the tube assembly in situ. First, the backhead was clamped to the wrapper using the scribed lines as a guide and the first pair of screws each side drilled and tapped similar to the front section of the outer wrapper. There was a large gap at the top that needed attending to, as can be seen by the torch light shining through.



My former obviously wasn't made accurately enough but it doesn't matter. Working on the inside, the flange was gently tapped down onto the wrapper working away from the screws. Then another hole was drilled and tapped, pulled up tight and work continued. Part-way through I dismantled it, cleaned up the holes and annealed the plate, then carried on. The soft copper melded to the wrapper quite easily.



This is how it finished up, nine screws used to hold the plate and a four-thou feeler not fitting through anywhere. Once again, these temporary 4BA screws will be replace with bronze ones at soldering time.



One last picture showing the boiler outer sitting on the bench waiting for the inner section to be replaced. I'm on track for a good soldering session at the end of the week.



Steve

[Deleted]

Excellent progress/work Steve...

Pete

[Midland]

Wow, what a lesson!
Thanks David