Vertical Boiler Project 4/3/11

Warning!!! The following articles are NOT plans for building a model boiler. There are no drawings or engineered specifications posted on these pages for a reason. These articles only serve as a record of my experience in building a vertical boiler. Please DO NOT try to use these articles as a guide to build you own boiler. They simply aren’t written for that purpose. Thank you...

Posted on April 3, 2011

       Hey folks!! This episode I plan to form out my end plates so they can be riveted to the boiler shell. To properly form the copper plates they will first need to be annealed from their “rolled” state so that they are soft enough to be hammered into shape. Annealing is done by heating up the copper to a dull red and then allowing it to air cool (sometimes water “quench” as well). This “relaxes” the copper atoms to an equilibrium state and removes any hardening that may have been induced into the copper during the manufacturing process.
       The annealing process will need to be done several times during the forming process so this should prove to be a good learning experience!!!

       To heat the plates up to a dull red I am using a MAP-Pro gas powered plumbing torch. I am using MAP-Pro gas in lieu of propane as it generates more BTUs than propane. In fact this torch is capable of heating up to  3600° F which is more than adequate for silver soldering (lead-free) and some light brazing. For now I just have to heat up these heavy plates which will take all this small torch has to offer!!

       I propped up one of the end plates on a piece of pipe and proceeded to heat the outer edge to a dull red. Since the plate acts much like a heat sink the heat quickly dissipates into the surrounding air so I heated the outer edge in a slow circular pattern. Once I was sure the plate’s edge was heated sufficiently it was allowed to cool. I then brushed off the oxidization and assembled my former plug as seen below...

       The former was now moved over to my vise where the plug and block could be properly supported (and clamped together). I then proceeded to start hammering the outer edge over the former plug side, rotating the former in the vice as I went around the edge of the disc. I “tapped” the disc edge in very small increments with a nylon faced hammer as to not “pleat” the edge, making complete rotational passes before hitting the same area twice.
       Note: It is very important to go slow or else you will wrinkle up the edge which can be very difficult to recover from....

       Surprisingly the copper behaved quite nicely for such a thick piece. However it was not long before the copper started to get tough and “work harden”. It will have to be re-annealed to be soft enough to continue the process.

       I removed the plate from the former and proceeded to anneal it for a second time...

       I was careful to not miss any areas of the edge as to keep the annealing evenly distributed.....

       And once again back into the former for my second pass. The softened copper was easy to hammer into shape with sort of a “dead blow” resistance but changed dramatically when it began to work harden. The hammer would start to spring back indicating that another annealing was in order...

       After several subsequent annealings and multiple passes with the nylon faced hammer I was ready to finish off the shape with a ball peen hammer. I was careful to evenly distribute the blows so that the outer surface was as smooth as possible.......

       Once I was satisfied with the shape of the disc it was removed from the plug and inspected. Surprisingly enough the shape was amazingly accurate in diameter and roundness :0)

       I moved over to the boiler shell for a fit check and was amazed at the tolerance that I was able to achieve with the wooden plug former. The end plate fit perfectly with almost no adjustment necessary!!!

       At this point I copied my forming process to create the second disc (not shown). This put me in good position to drill out the end plates for my boiler tubes.....

       To lay out my boiler tube holes I used an old method of overlapping circles as where the circles intersect at the center of each boiler tube. I had already scribed out a starter circle on each side of the plate before forming that would give me a starting point to work from. I could now add a straight line to bisect the pattern and keep the circles even (seen above).
       I decided to use a hole spacing of 0.830” center to center as it would leave a proper amount of end plate “bridging” metal between each tube (0.205”). If the “bridges” are too narrow it could promote cracking which is a common problem for full scale boilers. I used the guideline suggested in the
Harris book that states that the boiler tubes OD should not be spaced any closer than 25% of the tubes OD. In my case the boiler tubes are 0.625” in OD so:

                       (0.625” X 0.25) + 0.625” = 0.781” center to center

       I added 0.049” to the bridge thickness for added strength resulting in 0.830” center to center. Note: The actual diameter of the circles below are twice the center to center measurement equaling 1.66”. A center punch was used to define the intersecting circles and to help center the pilot drill later on.

       I could now start the process of drilling the 62 boiler tube holes in the end plates. I started out by drilling small pilot holes into the punched centers. This will help reduce the tendency of the larger drill bit from getting clogged by the copper chips.

       Both plates were drilled and cleaned up with Scotch-Brite “green” pads. This was done before the larger holes were drilled as it would be much easier to do beforehand....

       I decided to widen out my pilot holes with a 1/4” bit which will prepare the way for the use of a step-drill which will open up the holes to 5/8”.

       I decided to use a step-drill or “Unibit” to drill the boiler holes out as it is better suited to drill soft metal plate as opposed to a twist drill that would more than likely “snag” the plate and distort the job. A proper amount of cutting oil was used to keep the bit well lubricated otherwise it too would snag the copper plate and ruin my work....

       I carefully drilled out the first end plate making sure that I did not distort it along the way. One down, one to go.........

       I finished the second boiler plate after a few hours of careful machining. It was at this point that I wanted to sort out my boiler bushings before continuing on to drilling out the boiler shell. I had purchased a few small brass threaded bushings (seen below) for my boiler feed and sight glass fittings. Of course these are too small for my steam outlet and safety valves. I would need to make a custom set of bushings for these fittings..

       I decided to make my main boiler bushings out of 1/8” NPT cast red brass couplings (cast red brass is 88% copper, 10% tin and 2% zinc). Red brass is also called gunmetal which has a good resistance to corrosion. I cut the couplings in half to make six boiler bushings out of three couplings.
      
Note: Lead-free phosphor bronze is the material of choice when making boiler bushings. I chose to use cast red brass as it was readily available and easy to machine. Yellow brass (60% copper and 40% zinc) will quickly corrode as it has a high amount of zinc in it’s alloy which can be leached from the brass if put in direct contact with copper (galvanic action). Ultimately using brass alloys are frowned upon in boiler fabrication and should be considered accordingly...

       Using my lathe I was able to shape the bushings so that they could be silver soldered into the boiler shell later on. Note: I used an 1/8” NPT pipe nipple as an arbor so that the threads are square to the shoulder of the bushing...

       The shoulders of the bushings were cut to about 9/16” in diameter. A 9/16” hole will be drilled into the boiler shell later on to accommodate the bushings (which will be silver soldered into the holes). The inside edge of the threads were also chamfered to help promote good flow out of the boiler (seen below)...

       I now have all nine of the bushings I will need for the boiler shell....

       Please join me again next week when I drill out the boiler shell and prepare for the riveting process!! Till then take care my friends.....

Don R. Giandomenico - Novice Coppersmith :0)

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