kozo A3 switcher build

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sky
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kozo A3 switcher build

Post by sky » Thu Mar 22, 2018 2:43 pm

Hello,
This is my first build. I'm looking for help on the boiler. Kozo says to machine the arcs of the fire box, the backhead, and throat plate should I machine the straight edges too?
sky

Harold_V
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Re: kozo A3 switcher build

Post by Harold_V » Thu Mar 22, 2018 3:44 pm

If you're dealing with shorn edges, it's often a good idea to machine them, assuming you have excess material. They tend to include pent up stresses that often influence how flat a piece may be, to say nothing of the somewhat distorted thickness, where a sharp edge is formed on the bottom, often with some flashing, and a rounded upper face, where the blade makes the cut.

Note that I am not a boiler maker. Those who are may have a totally different view of the subject. I'm speaking from the position of the guy who used to build tooling for the aero-space industry.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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Bill Shields
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Re: kozo A3 switcher build

Post by Bill Shields » Thu Mar 22, 2018 8:48 pm

machine all edges so that you know what you have when you start assembly.

after you bang the copper around the formers, you get odd heights everywhere.
Too many things going on to bother listing them.

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NP317
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Re: kozo A3 switcher build

Post by NP317 » Fri Mar 23, 2018 1:08 am

Rule of thumb;
Any two surfaces that will be in contact should have machined edges.
Especially required for silver-brazed surfaces as used in Kozo's copper boilers.
~RN

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Builder01
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Re: kozo A3 switcher build

Post by Builder01 » Fri Mar 23, 2018 5:19 am

I have read Kozo's Pennsy book. He does show "machining" the surface of the flanged boiler plates by using a jig to run them by an end mill cutter. This seems like a pretty dangerous way to do it. The exception would be the smoke box tube sheet, as that can be done on the lathe. I have done my boiler plates by the normal flanging method of forming the plates around hard wood formers. To get a really good fit of plate flanges to plates, it is also possible to bring the parts together for test fits. The flange, or plate, can be knocked to fit the the other even if the surface is not perfectly smooth. Annealed copper is very soft and can be easily moved to fit almost what ever shape you need. Attached are a few photos of the fire box of my copper boiler. The fire box end plates are rather oddball shaped and it is not really possible or practical to "machine" the surface of the flanges. I just made sure the wrapper fit the end plates closely and the whole assembly silver soldered up very nicely.

The first photo shows the tube sheet of the fire box surrounded by the wrapper. In this photo, this has not yet been soldered. Two bronze and one copper screw allows this assembly to be test fitted. Assemble, check the gaps, adjust, and re-assemble. Do this over and over until everything has the proper gap for silver soldering. These screws are not drawn tight during silver soldering to allow the solder to flow completely around the screws. They are just there to "jig" the assembly together.

The second photo shows the inside of the joint between the firebox tube sheet and the wrapper. The flange surface and the plate were not machined. They were carefully made around a former and then adjusted as need until a good fit was achieved. The silver solder did the rest. This boiler passed it's complete hydro test in May of 2017.

David
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DSCN1148 - reduced 1.jpg
DSCN1182.JPG

Pontiacguy1
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Re: kozo A3 switcher build

Post by Pontiacguy1 » Fri Mar 23, 2018 7:20 am

Lovely work... I am envious. I've built probably a dozen steel boilers, but never a copper one. One of these days I'm going to have to try my hand at it, seeing as how I like to dabble in 1/2" scale 2 1/2" gauge, and virtually all 3/4 and 1/2" scales use copper boilers. Don't think a steel boiler with a 2 1/2" or 3" barrel would be a very efficient generator.

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Builder01
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Re: kozo A3 switcher build

Post by Builder01 » Fri Mar 23, 2018 8:36 am

The above copper boiler is for a 1" scale 4-3/4" gauge loco. And thank you for the kind words.
David

sky
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Re: kozo A3 switcher build

Post by sky » Fri Mar 23, 2018 8:55 am

Thank you all for the quick response and the pictures. I will mill the parts. Eventually would like to run the engine on propane. Any suggestions?
sky

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NP317
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Re: kozo A3 switcher build

Post by NP317 » Fri Mar 23, 2018 10:30 am

David:
Really nice work on the copper boiler!
~RN

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Builder01
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Re: kozo A3 switcher build

Post by Builder01 » Fri Mar 23, 2018 11:15 am

Thank you NP317 for the kind words.

For "sky", the photos and technique description was to show you what can be done without milling or machining the flange surfaces. Do the flanges need to be smooth and properly fitting, you bet! My emphasis was that these parts were not machined, just knocked or adjusted to fit each other in such a way that they would be workable for silver soldering. Nothing fancy or extra effort is needed.

David

sky
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Re: kozo A3 switcher build

Post by sky » Fri Mar 23, 2018 12:36 pm

David,
Your copper work is amazing. I don't think I have the skill or patience. I'm just hoping for no leaks.
sky

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Builder01
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Re: kozo A3 switcher build

Post by Builder01 » Fri Mar 23, 2018 1:03 pm

Sky, you will probably be just fine. Just allow yourself to be able to test fit things, make adjustments, then re-check. If you use a threaded fastener or two, as suggested by Kozo, it will make the test fits easier to do. Almost the entire boiler can be assembled without soldering anything if done this way. Although Kozo suggests brass for the fasteners, they really should be bronze or copper. I made my own 4-40 copper flat slotted screws and used commercial #6 bronze roundhead machine screws. The flatheads are not really that difficult to make. Especially since you only need a few, not hundreds. I would skip the commercial #6 screws and just use my own 4-40 flat heads if I were to do it again. Do not use brass for any copper boiler bushings or fasteners.

David

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