5" gauge Britannia (a builder's diary)

[David]

Your soldering is really neat. I'm amazed at how well the stays turned out with so much rework!

I wish I'd known of the idea of holding the tubes at the correct angle with a fixture when I did mine. Mine are way off and have a big bend in them... it will be interesting trying to fit the superheaters in them.

[springcrocus]

One of our members has sent me a PM querying the use of bolts for the crown stays. To forestall any argument arising and filling the diary with everyone's opinions about the pro and cons of this, here is a photo of the drawing which I will be working to. I will, of course, solder the screw heads.



Steve

[springcrocus]

I have now made all the bushes needed for the boiler, using either phosphor-bronze bar or offcuts of the pump house bronze plate. The clack, safety valve, blowdown and water gauge bushes were all straightforward turning with threads tapped to suit.



The regulator bush and it's coupling nipple have a 7/8" x 32 tpi thread and these were turned and screwcut on the lathe. The bush was made first, turning the top-hat form and machining the bore to 0.835" diameter, the nominal depth of thread for a 32 tpi Whit form thread being 20 thou. The bush was reversed in the chuck and a small register machined in the bore to allow the coupling nipple to screw up tight. Then, using a Whitworth-form screwcutting insert, the threading tool was touched on the bore and the dial zeroed. Multiple passes were made until I was seeing 40 thou (diametric) on the dial and a few spring passes made to finish.



The thread should be slightly undersize at this setting and if I need to acquire a tap to clean out the thread at some point in the future, there should be enough material to clean up.

I made the coupling nipple from hex bronze bar only because I have quite a lot of it. The end with the longer thread was turned first and the thread was screwcut right up to the shoulder, unpowered and pulling the chuck round by hand. The bush was used as a gauge, aiming for a free-running fit. The final size was marked on the cross-slide dial ready for making the other end. The component was drilled through and the 1/2" x 40 tpi thread for the steam collector pipe tapped at the same time.



To make the other end I used the bush as a mandrel to protect the original thread but that meant the gauge was no longer available, hence the marking of the dial.



As it turned out the thread was a little oversize so it was held gently in the chuck with a turn of emery cloth for protection and the thread chase freehand until the correct size was obtained. Not so easy with a single-point tool and a machine with no reverse on it.





Steve

[timo]

Steve,

Looking good - first pressure test is on the horizon - before Christmas???

Tim

[springcrocus]

Sept 13, 2019 14:53:53 GMT timo said:

Steve,

Looking good - first pressure test is on the horizon - before Christmas???

Tim

Hope so.

Steve

[springcrocus]

I have been busy making all the various holes in the boiler shell for the bushes and started by marking out the centreline along the top of the shell and measuring off the distances required. Because the drawing gives dimensions as a linear distance around the circumference a card template was made with the distances marked off. Using a template in this manner also ensures that the holes are square to the centreline.



Prior to drilling the holes, I fitted the front bung to prevent collapse of the tube when clamped to the mill. With all the handling recently it had gone a little out of shape and needed to be adjusted to fit the front tube plate anyway.



The dome bush hole was set up first and, as can be seen, it's a bit of a squeeze to get it on the mill. The boiler shell is resting on a pair of steel angles, clamped with whatever was to hand and then the centre found.



This one is a big hole and, after piloting with a holesaw, was cut using a boring head. I had to change the tool position half-way through as the head adjustment ran out of travel.



Just checking that the dome bush is a nice fit.



The top feed bushes needed a pair of 5/8" diameter holes and these were formed with a step-drill. Standard twist drills are a poor choice for drilling copper because of their tendency to grab the work and pull themselves in.



The two safety valve holes required 3/4" diameter holes and these were done in similar fashion but using the bench drill instead of the mill - not enough clearance on the mill to accomodate the throat plate. All packed up on timber blocks but no photo, I'm afraid. Again, with hindsight, it might have been smarter to make these holes before the throatplate was soldered on.

Steve

[Roger]

Excellent setups as usual Steve. It takes time, but the results speak for themselves.

[timo]

Steve,

Some really useful pictures and description.

Tim

[springcrocus]

The drawing suggests making the cross-stay heads from brass but I have made mine from phoshor bronze as they protrude into the water space. I machined the front end in a single setup, turning and threading the O/D plus drilling and tapping the bore and, finally, parting off to length.



I also made a mandrel to screw them into from some 5/8" dia brass bar with four flats milled onto it.



It was tempting to stand this upright in the four-jaw chuck and just wind round on the numbers but not really a smart move unless one has a left-hand-cutting end mill. A standard end mill or slot drill will always try and undo a right-hand thread regardless of the direction of the cut. They were laid flat in the vice and indexed over, working in the tightening direction.



A quick file all round and these are finished, ready for assembly and soldering. They are quite a prominent feature on the side of the firebox.



Steve

[ettingtonliam]

Neat!

[springcrocus]

In another thread I mentioned I was not happy with the shape of the firebox outer wrapper and had ordered a new piece of copper to try again. I redrew the angles onto the firebox former and made a new paper template to mark out the copper. I'm much happier with this second try.



The angles of the front throat plate, backhead and the fire grate are much more accurate now.



After getting the wrapper to be a nice fit around the front throatplate I set the assembly upside down on the bench and packed the front end to 7/16" high and the back to 3/8". This gives the correct shape to the top of the boiler.



The throatplate had to be eased back a little to match the bottom of the wrapper correctly and the wrapper needs a little trimmed from the bottom angles.



The backhead was offered in next and the firebox tapped around until a nice fit was obtained, then clamped in place. The backhead needs to be trimmed to length and this was duly marked off.



The backhead also needs the lower bend enhanced a little and this will be annealed and reworked.



Checking the length from the front of the barrel to the front of the throatplate showed it to be about 1/4" too long but, as can be seen in the picture, after the front of the barrel is trued up, this will come right.



Some heavy-duty tape was stuck round the barrel to act as a saw guide and the excess removed with a hacksaw and files. I also took the opportunity to load the inner firebox into place and check that sizes were all in the right ballpark.



Not looking too bad, a little bit of manipulation needed but nothing drastic.



All in all, it seems to be coming together quite well.

Steve

[delaplume]

Hi Steve,

Quote}---- "a little bit of manipulation needed but nothing drastic".......Well, given the general ductile nature of Copper in whatever hardness state then that's to be expected I suppose..........

I like the way each photo shows the Copper in that nice, pink finish....I think it wouldn't go amiss if you were to remind us with a photo or two --- especially for those who have never worked with copper before ----- just how much effort is required by way of scrubbing clean and rinsing in cold water each time any soldering has been carried out ?? ........

I'm glad you decided to keep posting.... this is exactly the way to help one another...

Alan

[twombo]

This IS, getting exciting! Alan put his finger on it, perfectly! your Well fit, and, Chemically clean, copper, are Master Class examples for us!

Without implying any advice, that you don’t need, how much will the boiler weigh, when the time arrives for the “ big heat?

My Marie Estelle, boiler package weighs about 25 Kilos. That is a concern for my future, efforts. The teamwork evident with your associate is pretty impressive , Steve! Moving that, big, heavy, and, HOT, thing is really something, Eh?

Aw. To be a fly on the wall, for this! A force of Nature! sir!

Good Stuff!

[springcrocus]

Alan, Mick, you both imply that I know what I'm doing: this is not the case, I'm feeling my way gently through this minefield, expecting it all to blow up at any time!

After the difficulty experienced with the outer girder stays, I decided that the outer wrapper would be fixed to the front throat plate with screws. I have some 4BA hex bronze bar in stock so this was chosen as the size and a good handfull of screws made.



Starting at the top of the wrapper, I drilled a 2.5mm hole right through with the pistol drill, opened it up to the 3mm tapping size, opened the wrapper part to 3.7mm with a hand drill and tapped the 4BA hole freehand. I drilled the 2.5mm pilot hole because I didn't want the tapping drill to cut oversize. This was temporarily bolted with a steel screw whilst the other holes were made in turn.



Once they were all finished, the clamps were removed and the back of the wrapper marked out to the final size and shape. I had left about an eigth of an inch to come off at the top, and the lower angle had to be set at ninety degrees to the bottom of the firebox.

After a pickle and clean, the manifold bush hole was marked out and drilled, then the bush soldered in with 38% silver solder. This also annealed the wrapper nicely for the next lot of fitting, and another pickle prepared the wrapper for soldering to the barrel.



Meanwhile, I have also soldered the various bushes to the boiler barrel using the same 38% silver solder. I'm just checking that full penetration has occurred. The boiler inspector saw this yesterday at the club, as well as all the other components, and reckoned I was good to continue.



Back in the workshop, the wrapper was refitted to the throat plate with the steel screws and the flange of the throat plate tapped about and the screws tightened a little more until there appeared to be good contact at all points.



From the outside, the wrapper was tapped gently down onto the throat plate, letting it follow the curve of the flange.



Once I was happy with this, the steel screws were removed one at a time and replaced with the bronze screws, which had just come out of the pickle and had a rinse. Finally, and for a change, I gave the whole of the outside a bit of a clean with scotch pad to make it nice and shiny.



This is now ready for soldering together, a job for next week.

Steve

[timo]

Steve,

Progress indeed and looking really good.

How much does the boiler weigh now? Must be quite a lot to move around when it is hot

Best Regards

Tim

[simplyloco]

Excellent Steve, and I look forward to next week!
John

[springcrocus]

Sept 22, 2019 16:29:53 GMT timo said:

Steve,

Progress indeed and looking really good.

How much does the boiler weigh now? Must be quite a lot to move around when it is hot

Best Regards

Tim

Tim,

I never move it when it's hot, I set it up in the correct orientation to accomplish the task in hand. I would rather cool it, clean it, pickle it and start anew with a fresh setup than move it around when hot. I'm not too fussed about the cost of the gas, unlike a commercial operation trying to make a reasonable profit. Not in a rush, either.

Since the two main sub-assemblies are yet to be joined, it's easily manageable at present.

Regards, Steve

[delaplume]

Didn't Bertie Wooster used to say "Top Hole, old chap" ??

[twombo]

Steve,

Your point re: movement. is well taken and filed away! Your growing experience is a great resource! Many of my previous mis-aprehensions of boilermaking are being. Clarified, watching your progress.

Some of the procedures that I envisioned, could have been. Very unwise or possibly unsafe! Thank You!
The progressive. Fitting, and assembling, that you are Showing us. The photo of the firebox, backhead, and boiler shell, fit up is very explanatory.

A picture is, a thousand words! That is SOME grate area, Eh?

Mick

[delaplume]

Hello all,

Quote}---- "That is SOME grate area, Eh?"......Indeed it is....It's pretty much the maximum for the loading gauge width and is on par with such locos as a Duchess, A3/A4, Merchant Navy / Battle of Britain and----some 30 years earlier----The Great Bear..I've used a Blackgates Britannia cast Iron one for initial design purposes...

Sorry Steve.......I'll tighten the thread and come back on-piste now,,,