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I need steam engine crank design info


I also considered making the cylinder head out of a bit of 6" ID pipe and then silver solder the steam chest to the outside. My biggest concern is getting the right methods to make it. I have a 9 x 20 lathe and a Seig Super X3 mill.

Any thoughts welcome.....



Your machine tools are in no way going to be close to adequate for a job like this. I advise cultivating someone with a decent machine shop ASAP.

Also there's no way I'd be silver soldering the bits together. You do realise there's quite a strict boiler code and from what you've posted so far I don't think you'll comply with it. However I'm not a steam guy.

Find a live steam loco club - there are plenty about the place. Talk to the members, likely a lot of them have built their own locos, have decent machine shops and understand what's needed to get a boiler certified. You need to sort this FIRST before thinking of the engine. A boiler is a potential bomb and one in an urban area really needs to be over-engineered, not kludged.

Here in the USA, when we design boilers or alterations to them, we use a minimum factor of safety of 5. Member John Ruth has posted the quote: "Boiler Codes are written in blood". It is no small matter to design and build a boiler. A boiler has the potential to rip apart catastrophically should it fail in service. A flash type steam generator is basically a long coil of tubing. Heat is transferred into this tubing, and water must be fed through it continuously. It forms steam in a relatively small space, and requires a more delicate balance of feedwater flow matched to steam demand than most boiler designs. it also requires close control of the firing rate, almost instantaneous response to changes in steam demand. One of the few plus's to flash steam generators is they have little contained volume of water or steam. Should the coiled generator tube rupture, the result is more localized and contained.

Running a flash steam boiler (sometimes called a "monotube" type) non-condensing is yet another matter. If a steam plant (engine, boiler, pumps, etc) is run non condensing, the steam is exhausted to atmosphere and no condensate is recovered. This means make-up water must be continually supplied for feedwater. This makeup water has to be tested for dissolved minerals, pH, oxygen content, and suspended solids. It then has to be chemically treated to adjust the pH (slightly alkaline is required), get rid of dissolved oxygen (otherwise, oxygen pitting is a given), and to cause the dissolved minerals (aka, "dissolved solids") to precipitate out.

Raw water will vary in its chemistry, even from town mains, and it varies seasonally or even more frequently based on activity in the aquifers or other sources. If chemistry is left unaddressed, in a boiler like a flash steam boiler, the effect is a buildup of scale in the coiled tube that is the "boiler". A common example of this is a tea kettle which has been used to boil water over a period of time. Scale can be seen within some kettles. Similarly, steam irons, used to iron clothing are usually filled with distilled water to avoid scaling the internal steam generator.

On a flash boiler, if the coiled tube scales, the effect is a loss of heat transfer to the water within the tube. At the same time, the tube wall will get excessively hot, and can reach a red heat since the scale will be acting as an insulator- the water within the tube being unable to absorb as much heat as from an un-scaled tube wall. When the tube wall reaches a red heat, the steel is plastic, and the internal pressure within the tube will cause that area of the tube to bulge. This bulged area will have a thinned wall, and may rupture. Once that happens, the water under pressure and at some higher temperature (even with the scaled tube wall), will rush out of the rupture and flash violently to steam. This expansion is instantaneous, and the difference in volumes from water to steam may be as much as 1200-1500 times per unit volume. This expansion produces a ripping action on the tube, and what was a small localized rupture will "unzip" into a larger opening. At that point, the furnace or firebox is filled with steam and possibly slugs of hot water, and the rest of the boiler-particularly if solid fuel fired- is going to become a mass of red hot tubing in short order.

As I said, the only up-side to a monotube or flash boiler is the failures tend to be localized and failures are dealing with smaller volumes of water contained within the coiled tube.

I am unsure what you mean by saying you want to build a "cylinder head" out of pipe. A cylinder head is a cover or plate which closes off the end of a cylinder. I am assuming you mean the cylinder itself. Either way, if you intend to build a cylinder out of steel pipe, you need to use complete penetration welds (known as CJP welds or full-pen welds) to tie the flanges to the tube. Similarly, when you make the piece of steel with the steam passages and ports, this should be machined to a good fit to "saddle" onto the tube that forms the cylinder. Once this piece is fitted to the cylinder, it should be secured with fillet welds run between the sides of the steam-passage/port block and the cylinder and the end flanges.

Silver soldering is for building smaller engines such as models, and for fine work on small parts. It has its place. For something like a 4" x 6" cylinder, you will break the bank buying silver solder and oxygen and acetylene. I recently bought a "silver brazing coil" at my local welding supply. It is for silver brazing of copper-bearing alloys and austenitic stainless steels. 5 Troy Ounces of sil-braze wire stood me 105 US dollars. I do not know if you ever ran real silver solder (aka silver brazing). It requires very precisely machined and fitted joints, careful use of the torch, and a lot of the silver brazing alloys will run like water once melted. A properly made joint will only have a few thousandths of space and with the heat properly manipulated, the silver brazing alloy will "wick" into the joint. A little of it goes a long ways. What I prefer to use for this sort of work is silicon bronze brazing, on thin parts and fine work, or for dissimilar metals like copper bearing alloys joined to ferrous metals or stainless.

For something like a 4" x 6" engine cylinder and steam chest, I would have no problem fabricating it using stick (Shielded Metal Arc Welding or SMAW) with E 6010 (a "digging"/fast freeze electrode) and E 7018 (a combination fill/freeze electrode). I routinely fabricate parts using stick welding and then machine them to finished dimensions, including thru the welds. The result is homogenous steel, and sound welds that show no porosity or slag inclusions or lack of fusion. Silver brazing on something so large as a 4" x 6" engine cylinder is an invitation to incomplete joints and leaks in the least case. The US Navy learned a very costly lesson about silver brazed joints on piping with the loss of the nuclear submarine "Thresher" in the 1960's. She was lost with all hands during a test dive following a shipyard refit. After lengthy analysis of underwater photos and wreckage and records of work performed, the cause was laid on the failure of silver brazed pipe joints due to incomplete joining failing under pressure when the sub went to something like its test depth. The US Navy promptly put a stop to using sil brazed joints on piping.

A 4" x 6" engine is a serious engine, and will require a real machine shop to build, as well as SMAW or TIG welding to fabricate the parts. A 13"-15" swing engine lathe, a mill similar to a Bridgeport (or a little heavier) is what is needed in the shop. As for the boiler, do not touch that matter unless you are prepared to do the engineering. I recently ran a set of calculations on perhaps the simplest vertical firetube boiler imaginable. I think there were about 30-40 pages of calculations.
If you look in boiler codes (we use the American Society of Mechanical Engineers, or ASME, codes here in the USA), you will find tables listing various steels and their strengths at elevated temperatures. You will find the strengths of steels diminishes as the working temperature rises. To design a boiler of any sort, you need to know the type or grade of steels you are working with. Grabbing a chunk of pipe is not good enough. Is that pipe seamless drawn or butt welded ? What grade of steel is made of ? How can it be welded -what weld procedures are to be followed, any preheat or postheat ? What qualifications must the welder doing the work have ? This is the sort of thinking you have to do when you start thinking in terms of designing, let alone building, a steam boiler- even a small one. Simply slapping pipe, plate and fittings that are found in the local salvage yard together with a MIG welder or by silver soldering is not the way to build a boiler.
Well I wanted advice and I got it, thanks for everyone who contributed.

Some of you no doubt figured I'd be dead withn 6 months after building stuff, I was aware of bad boilers flattening city blocks and water cracking into hydrogen after hitting hot steel and resultant explosions , but its good to have a reminder of dangers.

I may yet press ahead with my plans, but it will take a lot longer than I thought due to the amount of learning etc I'll need to do. Thanks for the warning about silver soldering and pressure. I do have a stick welder rated to 140 amps, not sure if that will be enough. Once I know the thickness of steel I need I'll be better placed whether to buy a decent welder.

I've probably been a bit loose with my definitions so please excuse that, I'm not used to the lingo, but am learning.

The main reason I wanted to use a flash boiler was that it ( within reason ) wouldnt be a "bomb", and I was aware of the need to descale it so it wouldnt fail. I assumed I'd have to run pressure tests from time to time to check for leaks etc but am willing to admit there is still a lot to learn.

I have an engineering background, but the world of steam is a different beast and hard to visualize the dangers at times, so my questions have been general and what seem like ill-informed questions are just the basis of taking initial learning steps and taking my next "bearing" from, as I hone and develop knowledge.

I think so far a smaller scale engine might be the go, and see if I can natuarlly scale up from there. Just building the flash boiler will be interesting, just out of interest, which is the better tube material for longevity - copper of steel, for a flash boilers internals?


I think so far a smaller scale engine might be the go, and see if I can natuarlly scale up from there. Just building the flash boiler will be interesting, just out of interest, which is the better tube material for longevity - copper of steel, for a flash boilers internals?



Seriously, find a live steam loco club & talk to the members. They will be au fait with the local boiler test rules along with a ton of other stuff.

There's an Aussie metalworking forum with some active members around the place. Quite a few in Melbourne & Sydney, less but still some in Adelaide, Brisbane & Perth. Hobart has me & a couple others, we're not steam people though but do have pretty comprehensive machine shops (your mill would fit on the table of my baby horizontal boring mill). Can't suggest anyone even via a PM because your location as 'Australia' is pretty useless.

Wokka -

I'm glad that you are having another think about your project and I hope your enthusiasm is not dented by the advice that has been given.

I think the best way forward if you want to build your own model engine and boiler is to join a local model engineering society. In UK these clubs provide a lot of help to people who want to undertake projects like your own. They usually have some very experienced people who will get you through some of the engineering problems you will face and can help you gain the skills that you may need. Some of the clubs also have their own machine tools that you might be able to use for specific jobs. They also look after boiler inspection against some fairly tight codes so that you will end up with a boiler that is safe and insurable. In UK the main emphasis is on locomotives but there are lots of people building other types of engines and boilers as well. For example, I vaguely remember a series in one of the model engineering magazines about the building of a small Yarrow boiler (water tube design) which I thought was very interesting and obviously nothing like the typical locomotive boiler.

I am not a member of one of these societies, but I do know people who are and they do get a lot out of their membership. In UK most large industrial towns and cities have model engineering clubs. Australia may be a bit more scattered, but I have read about similar organisations over there and their boiler inspection schemes. Hopefully one of the Australian contributors can point you towards one that is near to you (where is that?)

----- PDW just beat me to it with his message so good to see confirmation that there are clubs like this available to you down under. ------
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The US Navy learned a very costly lesson about silver brazed joints on piping with the loss of the nuclear submarine "Thresher" in the 1960's. She was lost with all hands during a test dive following a shipyard refit. After lengthy analysis of underwater photos and wreckage and records of work performed, the cause was laid on the failure of silver brazed pipe joints due to incomplete joining failing under pressure when the sub went to something like its test depth. The US Navy promptly put a stop to using sil brazed joints on piping.
That's not the best theory anymore ... there's a lengthy analysis of the accident which concludes that the reactor shut down from a minor cause when she was almost at test depth. With no power she was headed down and couldn't climb back up. The reactors at the time took more than five minutes to restart. She tried to blow but the pipes were too small and froze up. Then she exceeded crush depth by several hundred feet and imploded.

The only good part to the story is that at that depth, crushing is so fast that it exceeds the sensor speed of humans, so the crew literally never knew what happened.

Thanks everyone for thier thoughts, i figured some wise people would be happy to provide guidance.

There are many considerations around the whole project which is really 2 ( boiler and engine ), and so far i think i have a lot of research to do, but you guys have helped a lot.

I'm pretty sensible, smart enough to ask about this potential venture from people who know.

The local miniature steam mob i have talked to in the past, trying to work out the best design for a steam slide valve, which worked successfully, but more consultation is no problem....

The biomass boiler using alternative type of fuels will take some playing with. I dont think the system will run unattended, more likely 4 hours per day to charge batteries.



You are correct regarding the loss of "Thresher". The root cause was laid to the failure of some silver-brazed pipe joints. As I understood the findings of the investigation, the leaks themselves were small. However, the leaks were at the full pressure of the sea outside the hull. The sea water from the leaks sprayed onto or into electrical systems controlling the reactor. The reactor shut down and with it, tripped the main propulsion turbine and ship's steam turbo generators off line. Why the sub did not recover using emergency battery power is something which has occurred to me. A great deal of redundancy is built into submarine systems and the crews are incredibly well trained.

I know the investigation seemed to settle on the matter of the silver brazed pipe joints, and the fact that there was a combination of inadequate inspections due to a waiver of the amount of inspections required. This was done in order to get the sub out of the naval shipyard to meet some schedule. Apparently, there really was no good non destructive testing method (NDT) available at that time (early 1960's) that could readily be used in place on the pipe joints. The method was visual inspection, which did not disclose how much "wetting" of the joint surfaces had occurred. About all the inspector could see was a fillet at the outer circumference of the joint and evidence of improper heating of the joint. The people doing the brazing were tested by sectioning test joints and determining if a full "wetting" of the mating surfaces had occurred. Once a brazer had passed this bench test, he was put to brazing pipe joints in the sub. A lot of these joints were out of position or in tight places, and the silver brazing was being done on copper bearing alloys as well as stainless steels. In the 1960's what we now know as "TIG" welding was in its infancy and was known more often as "Heliarc" welding. It was a process used mainly in fab shops for "bench work", if at all. Since the 70's for pipe work similar to what let go on "Thresher", the joints would be TIG (or more correctly, GTAW) welded and likely checked with ultrasonic inspection.


I am glad your enthusiasm has not been dampened by all we've posted. There is a lot to learn in the design and building of a steam plant. As was written, a good starting point is to get connected with a "Model Engineering" group. Another really good starting point is to build a smaller model steam engine in your shop. This will give you practice in making the various parts, and at least as importantly, getting them machined with proper tolerances so they fit together and produce a working engine. Building an engine from plate steel and bar stock is a good starting point. Something of manageable dimensions on the order of maybe 1" or 1 1/2" bore would be what I'd suggest. The parts are big enough that you can manage them with a little looser tolerances. Smaller model engines require a much finer degree of accuracy, and require tapping some very small threads. I can speak from experience that when I have to tap a 2-56 thread (as was the case on a model engine a young fellow who was my
"apprentice" was building in my shop), we both held our breaths and joked about nor burping, passing gas, or doing anything sudden lest the small tap be broken off in the work.

Build a good sized model and you will learn volumes.

Your 140 amp welder may surprise you. The rule of thumb for stick welding is 1 amp of welding current per thousandth of an inch of electrode diameter. A 140 amp welding power supply can supply enough current to burn 1/8" diameter electrode. For smaller work such as you might get into in building a model engine, you would be burning 3/32" diameter electrode, so would only need about 90 amps + or -, based on position of the weld and rod type.

You are on the right track in your approach to your project. I'd also suggest you find a steam power club if such things exist in your neck of the woods. Steam power or old machinery groups may have full sized steam power such as traction engines or portable steam engines that they run at events. If you can find such a group, you would then get a sense of what running a smaller but full size working steam plant is about. You will get ideas as to what it takes to fire a boiler, maintain a head of steam in response to engine load, and what it takes to look after the engine, how a governor works, and so much more.

I teach a course at Hanford Mills here in NY State that I put together a few years back. It is called "Steam Power 101". It is a very basic course given over a weekend. We cover a lot of ground, starting with some history, some engineering basics, and move into how a boiler produces steam, types of boilers, stresses acting on parts of a boiler, boiler design and construction, boiler codes, safety valves and how they work, then hit the thermodynamics of how a steam engine works as well as how an injector works. We do a lot of "hands on" which includes firing the horizontal return tube boiler (hand fired on wood) in the Mill steam plant, raising steam, working the injector and steam feed pump, warming the piping and engines, lubricating, starting and running the engines and seeing them come on and off load. We gear the course to each group of participants, so if we have people who are enthusiastic but do not know a pound per square inch from a pound of beans, we start there. If another group is more learned technically and more mechanically experienced, we jump in further into it.

Unfortunately, you are on the other side of the planet, or I'd invite you to attend as my guest. I will be giving the course again this weekend. If you PM me with your address and are interested in seeing it, I can send you a copy of the manual I wrote for the course. It is about 100 pages of information that distills down a variety of subjects, both theoretical and practical as they relate to simple steam plants.

Like anything else, this sort of project is kind of like starting any journey. If you look a long journey in the face and see its entirety, you might not want to get out of bed to start on it. If you do what I call "chunking it up" into manageable and finite sections, it becomes do-able. I can remember sitting examinations in engineering school (we go back about 45 + years to that point in my life). I'd look at the exam paper and get rattled, heart's governor not doing much with my heart racing into overspeed and lungs not far behind and gut tightening like a hose clamp was cinching tight on it. I'd have to trip my governors, stop for a few moments to re-set and re-start my own "plant", and begin reading the exam paper, scanning it for a problem that looked readily "do-able". I'd get that problem done, and find another, and work around the exam paper, sometimes gaining information by slowing down to work one problem and using it as a step-stone to another. As I entered my career, I got into more and more complex projects. I learned to follow that "chunking up" rule. Even taking trips on the road, I follow this approach. I can climb on a motorcycle heading to a place like Omaha, Nebraska from NY State. If I look at the distance, I will say: "Are you crazy to do it on a motorcycle... You always run into a day of rain across Ohio and clear to Chicago... " Then, there is the part of me which says: "If you DON'T make this run, you will find reason to not do something else along the way, and next thing you know, you will not want to get out of bed..." So, I climb on the old horse and say: "We'll do a hundred or so miles and stop for gasoline." I look no further than that. No thought as to the next day's weather as the die is cast and I am on the run, and no amount of thinking about the weather will do anything other than stress me. After the first fill of the gas tank, I get in my groove, and just "go with the run". Omaha, Minneapolis, or wherever, I chunk up the journey, do a little mental math as to mileage, fuel economy, time, and whatever else comes to mind. No radio or CD player, just the wind past my helmet and the sound and feel of it all, and my mind for company. If I am sitting in a waiting room for a dental appointment, or in airport waiting to catch a flight, I am using my mind to design things, running mental calculations. A piece of blank paper, a few minutes and a pen are great entertainment for me.

Get familiar with the basics of what you need for the design of your steam plant and start sketching and "playing with numbers" as I call it. It is a constructive use of odd amounts of slack time, and will help you "chunk up" your project. You will burn up plenty of paper and sharpen your mind in the process. That is perhaps the most important thing to develop and the worst thing to let get atrophied from minimal use. A project like this is great exercise for your mind as well as your body when the building starts.
You are correct regarding the loss of "Thresher". The root cause was laid to the failure of some silver-brazed pipe joints.
Search around a bit if you are interested : that's exactly what this analysis denies. He goes into the sound recordings extensively to come up with a different scenario.

His case is very good and I have a tendency to believe it, because historically in cases of disaster the brass loves to blame the workers. Essentially, a submarine that can't power itself is a stupid design failure. But we would never want to blame the highly trained upper class leaders when we can blame the mouth-breathing union shipyard workers instead.

A friend of mine did piping at Mare Island and turned me on to this study, it's worth your time. Ed made a wrong turn one day into a hot area, had to throw away his badge, a couple years later got a phone call, "Going in to remove a brain tumor in an hour, if you don't hear from me bye-bye" and that was that.
Sea Moss:

I am sorry to read about your friend. I worked as an engineer for Bechtel assigned to the startup group on two nukes, and that is over 40 years ago. The fuel had not been loaded at either plant, and I was moved back to construction of a fossil plant- which is the job I'd been waiting for back then. A buddy of mine is about to retire from my former employer- the NY Power Authority. He told me he is all set to go to work on an outage at Indian Point, a nuclear plant slated for closure in 2020. He's going on the outage as a contract hire and will be supervising various crafts. I kept my thoughts to myself. This guy had worked for some years at Indian Point before it was sold to a private power plant operating company. He knows the plant and what he's getting into, but I would not go near outage work on a nuke.

I will look up the studies on the loss of the "Thresher". As you note, it is convenient to blame the crafts and claim poor workmanship on their part. With the sub on the ocean floor and some undersea video or photos of debris to try to make some sense out of, it is easy enough for someone like myself to go with the official findings. However, having worked startup, I was in with a bunch of guys who either had been civilian engineers for Admiral Rickover at the prototype reactor plants, or who had served aboard US Navy nuke subs. These guys were all extremely sharp and quick, and they took a hand in developing me. Having worked with enough men who'd come thru the US Navy's nuclear power program, I still find myself wondering what happened in the last minutes aboard the "Thresher". Sub sailors were always cross trained so they could have familiarity and be able to step in and operate other systems on the subs than what their own designated assignment was. Nuke sailors were especially well trained, and drills and practice were a constant. This has me wondering how, if "Thresher" lost her reactor plant due to an emergency shut down, things like an emergency bus fed off battery banks did not kick in, and why her crew did not take control of the sub using emergency power to blow ballast and get her surfaced. Possibly, the sub had plenty of speed and down angle, and things happened too fast for any sort of emergency procedures to be implemented.

I know in the powerplant I retired from, the operations department constantly was having training and drills. The result was we could have something like 500 megawatts ready to go into the grid from a black start in well under 5 minutes- this being a pumped storage hydroelectric plant. We actually black started parts of NY State following an ice storm, and again following the blackout of 2003. We moved like a well oiled machine. We had guys who were ex nuke sailors in the operations department, and these guys held things to the kind of standards they knew from the nuke navy. I was proud to work with them, and we were all proud of our plant and its record.

I think of the caliber of those guys, and the guys I worked with at Millstone II and Davis Besse I, the two nukes I worked at, and wonder what happened aboard "Thresher" with that caliber of person in the crew. Whether there were design issues in the way the sub's power circuits were configured that prevented an emergency blowing of ballast if the reactor plant were lost is something I'd be interested to find out. I was a kid of 12 when "Thresher" was lost. It's something that I find myself going back to, and with the scuttlebutt about the failed silver brazed joints, it was an explanation I could relate to and understand. The pressure of the sea at a sub's test depth would produce pressure in any piping connected to a through-hull fitting of several hundred psi. Add vibration and shock loads and the failure of a silver brazed pipe joint becomes quite believable and something I swallowed easily. Given your post, I do intend to look further into the loss of "Thresher".
... why her crew did not take control of the sub using emergency power to blow ballast and get her surfaced.
They did blow. The pipes were too small so the gas velocity was too great, then pressure drop caused ice to form in the pipes so the air couldn't get through. They might have been okay if they'd been more casual about it, but under the circumstances ... :(

That's one thing they did correct post-haste. There were a bunch of things changed post-Thresher and retrofitted to the other boats.