Calbourne - 5" gauge boiler

[springcrocus]

I have started a build log for my Adams "O2" locomotive in another section but wondered if members might be interested in how I constructed the boiler as a separate topic. I'm not a very experienced boiler-maker so it might help someone who is contemplating making their first boiler. I am in the UK and it has to comply to the current UK boiler regulations which differ from the rules elsewhere in the world.

Also, we can no longer purchase cadmium-bearing silver solder so the boiler has been constructed entirely with cadmium-free solder, which is a completely different beast to the old stuff. It flows like water, for a start. I had a colleague assist in the making because I've found that it is much easier with two torches on the go when it comes to silver-soldering large masses of copper.

Amongst the first things I made were some formers for flanging the various end plates. I made these from 20mm MDF as I have used this before and found the material works a treat. The front and back firebox plates are the same size and have a large radius at the top corners. I drilled a 5/16" diameter hole at the origins of the two circles and used these as pivot points on the rotary table. I also machined a small radius to the outer edges using a router cutter so that I dont end up with a sharp corner inside the flanges.



Two other formers were made at this time, one for the front tube plate and one for the backhead but the one for the throatplate was made once I had the outer wrapper shaped. The second hole in each former gets used as a means of stopping the work rotating about the pivot by clamping to a tee-slot.



I decided to make the front tubeplate first using a piece of 3mm copper. I roughly cut out the shape, then placed it between the former and a solid backing plate and held it in a bench vice. Then it was a case of some firm tapping followed by annealing at red heat and plunging into cold water. The plunge isn't strictly neccessary as the copper goes soft anyway but it flakes off any scale and speeds the job up. It took two annealings to get this far.



I was cutting off surplus waste with a hacksaw as I went but it was getting more difficult to keep the shape the further round it went so I used the lathe to trim it down when I was about ninety percent of the way there.



Once I had the copper firmly on the former all the way round, I then skimmed the O/D  and faced the back. The only way I could find to hold the tubeplate was with my 4-jaw SC chuck because the 3-jaw wouldn't go down far enough. I turned it to about 10 thou oversize, then trimmed it to length using a left-hand tool.



The barrel was then returned to the lathe and mounted in the home-made fixed steady so that I could bore it to fit the tubeplate. It needed to be 1.1/2" deep to allow the plate to sit at the correct depth. I only use those super-sharp polished carbide tips for turning copper because ordinary tips tend to be useless with soft materials.



By having a small shoulder, it also means I didn't have to use any fixings to hold the tubeplate in place at soldering time, gravity did the job for me. At this point, it's a nice sliding fit but it will probably become distorted during the various  operations between now and then so will needs tweaking at the time.



Then it was time to put the holes in and this was done on the mill using the DRO to locate them all. I used an 8mm drill to start with, then followed with a series of slot drills to get the holes to size. The 10mm tube holes needed the reamer run through and the superheater tube holes were bored but the three remaining holes were just left at whatever as the bushes will be turned to fit. Offcuts of tube were used as gauges.



Firebox endplates next.

Regards, Steve

[Jo]

You are making it look easy Steve  It takes a lot of bashing to get the smokebox tube plate to turn into a dish. Out of interest what type of hammer did you use? We had a discussion the other day to see what people used and it ranged from use a wooden mallet, plastic, through to good old engineers bashing hammer and a few in between   

That tip seems to be cutting the copper very nicely 

I haven't tried the Cadmium free Silver solder (yet) so I will be interested to see how you get on with using it.

Jo

[springcrocus]

... Out of interest what type of hammer did you use?

Jo

Nothing special, just the nearest one to hand, usually a 1lb claw hammer. Like I said in my intro, knife-and-fork merchant. 
I can't afford any of those fancy planishing hammers.  :'(
Regards, Steve

[Kim]

You are making it look easy Steve  It takes a lot of bashing to get the smokebox tube plate to turn into a dish.

I'll say!  The boiler I'm currently making is simple compared to what you're doing!  I've only got 3 tubes instead of the multi-dozen you have.  You're just making it all look so simple!

And yes, I used soft faced hammer (plastic head).  It's a cheap one from Harbor Freight that I've had for years. But it worked. Supposedly didn't mar up the copper, but clearly you had no problems with the claw hammer! You made it work quite well!

I'm certainly enjoying seeing how you did this! 
I've got a lot to learn!

Thanks for posting!
Kim

[Mcgyver]

Nice work.

What radius did you put on the former, and what gauge copper?   Just trying to get a sense of what works.

[springcrocus]

Nice work.

What radius did you put on the former, and what gauge copper?   Just trying to get a sense of what works.

The copper barrel and front tube plate are both 10 swg (3mm) and the bore of the barrel is 4" diameter. I used a 5mm radius router cutter for the  former edges.

Regards, Steve

[springcrocus]

I've just realised that I forgot to describe the barrel before showing it being bored for the front tubeplate. 

The barrel is 4.1/4" outside diameter and has been machined to length by holding in the bore and supporting the other end in a steady. My steady wasn't large enough to use the rollers so I set some PTFE pads on the outboard ends of the arms and then reversed them. With a drop of lubricating oil, they worked fine. This isn't locked down yet but it shows the pad in place



Although it had been sawn reasonably square and didn't really need to be cleaned up, I faced about 20 thou off the first end. However, for some unknown reason, I ordered an overlong piece and decided to part the surplus off. The ring will come in handy one day. I cheated, though, I only parted about three-quarters of the way through then hacksawed the last bit before finishing the face with the parting tool.



More of the boiler parts have now been made including the firebox endplates and the backhead. These have all been melded around their respective formers and the workshop became quite hot with all the annealing that was needed. In case anyone has never annealed a piece of copper and was wondering how hot to get it, it's this hot!



Because the formers won't be needed again, they were used to support the work while the edges of the flanges were machined to size. The copper is still very soft at this time and will bend away from the cutter quite easily. I used a 1/4" diameter end mill to trim the edges, going round in a clockwise direction (climb-milling) to give the material maximum support.



The former was also used as support when I milled the endplates to length.



The firebox tubeplate was drilled in similar fashion to the front tube plate, the rear tubeplate has had the firehole bored to size and the backhead has been fashiond around another MDF former.



The tubes were expanded at the back end by about ten thou, then skimmed back to just under 10mm so that there is a tiny shoulder for the tubes to rest on when silver-soldering. Nothing is needed at the front because the front tubeplate will rest on the lip in the barrel. Some 6BA bronze screws were made and these have been used to fix the wrapper to the end plates. I don't like rivets for this because they don't hold the work firmly enough.



Also completed were the holes in the barrel for the forward clacks and the large steam-dome hole. The front tubeplate was used against the chuck jaws as a depth-stop and an MDF former bolted to a faceplate acted as the support for the other end. After drilling and reaming the two clack holes at plus and minus 90 degrees, the rotary table was set to zero and the big hole roughed out with a hole-saw before boring to size.



Once this was complete, with the rotary table still set at zero degrees, a scriber was mounted in a drill chuck and dragged along the full length of the barrel. I didn't do this on the Britannia boiler and had alignment issues because of it.

Regards, Steve

[Jo]

What are you using as your pickle, Steve?

Jo

[springcrocus]

What are you using as your pickle, Steve?

Jo

Citric acid. I bought a 5Kg tub of food-grade from Amazon for about £20 originally and it makes a dustbin-full of pickle.THIS is their current offering.

I use a damaged wheelie bin that the council were discarding.

Regards, Steve

[samc88]

Nice boiler work, it all looks very neat

[vtsteam]

It's an eye opener seeing that hole saw work on that round copper sheet and do such a nice job of it. 

[Kim]

It's an eye opener seeing that hole saw work on that round copper sheet and do such a nice job of it. 

Yes, that's interesting for sure!
Was the copper tube half hard or fully annealed?  Seems like it would be harder to do the hole saw if it was annealed. Just curious.

Kim

[springcrocus]

It's an eye opener seeing that hole saw work on that round copper sheet and do such a nice job of it. 

Yes, that's interesting for sure!
Was the copper tube half hard or fully annealed?  Seems like it would be harder to do the hole saw if it was annealed. Just curious.

Kim

This had not been annealed, just as delivered from the supplier. I used the same method on my first boiler and that one was annealed but no problem either. I expect the barrel shape is self-supporting.
Regards, Steve

[springcrocus]

The outer wrapper had a centreline scribed at the half-way point and was simply folded around the barrel, followed by bending back to form the waist and creating a nice fit around the backhead. Then it was on to the throatplate.

This was the most difficult part to make because of the reversed double flanges and I cut the raw material a good one inch bigger all round than the suggested starting size. I also cut a packing piece for the front of the wrapper, clamped the backhead to the bench and temporarily assembled things to get a feel for the finished shape and size. The offcut of tube was used to mark where the barrel reaches to.



Learning from my experience with the Britannia boiler, I decided to get the side flanges fully-formed first and a piece of MDF was made into a former. I could have cut down the backhead former and used that but it was just as easy to make a new one. No pictures here, it was just simple folded-over sides. The former for the barrel flange was a little more complicated and a piece of oak kitchen worktop was used to make this, squared-up all round and milling out the middle to support the side flanges. The top was shaped using a 110mm hole saw.



The first former was cut down to act as an internal support but allow the flange to be formed and the throatplate was placed in the former and the flaring at the top beaten into place. Some of the waste area was marked for removal and was cut out with the Abrafile before I started to form the barrel flange.



I found early on that the sides of the former would need support and a large clamp was used with the rest just held in a bench vice. I don't have any special hammers for copper-forming and a one-foot length of 1.1/2" diameter stainless steel was used instead because of the concave form.



Between the many annealings, I kept returning to the mill to remove excess material because the further I went, the harder it got to keep the shape. This is the point that I decided to call a halt to the bashing and bring all the flange widths to size although the picture was taken after thinning the top wings.



So this is a trial assembly to see how well things fit and it's not too bad. The circular shape wasn't perfect, however so I decided to skim a little off the inside using a flycutter.



I don't have any left-hand tools for the boring head so set up a right-hand one and ran the mill in reverse. This promply unscrewed the head from the mandrel so I had drill and tap a hole in the side to accomodate a locking grub screw. After that, I milled the diameter to a near-perfect fit. Once again, the former acted as a support for the soft copper and the opportunity was taken to scribe a centre-line through the workpiece.



A pair of fixing holes were drilled in the barrel flange and this was then rested on the barrel using a large vee-block to get everything in line and upright. The holes were transferred through to the barrel and a pair of 6BA holes tapped to take some bronze screws at soldering time. Another centreline was scribed on the underside of the barrel, diametrically opposite the top one. This enabled accurate alignment of the throatplate.



Another fixing was made to hold the wrapper to the barrel and the assembly held together with clamps. I can now mark out a few more fixings knowing everything is square and correctly aligned. I won't make any fixings for the backhead yet, though, because things like the firehole ring and the foundation ring will determine the final position of that.



Regards, Steve

[Admiral_dk]

Great looking parts so far  but I bet that the moment you noticed the Boring Head starting to unscrew was a heart stopping one 

Will follow with interest     

Per