Author Topic: A Simple Uniflow Engine  (Read 7146 times)

Offline gary.a.ayres

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A Simple Uniflow Engine
« on: April 27, 2020, 12:11:04 AM »
Hello All.

It has been a while, what with everything that is going on.

Hope you are all ok...

Finally and at last, I have made a start on my second engine. A slightly unusual one, this.

First of all, the 'simple' in the title of the thread refers to the simplicity of the concept of the engine. It does not mean that I think I'll find this build simple.

The design upon which I am basing the working heart of the engine is by Stan Bray. It's 'Clarence - a clapper valve engine'' from his book on building simple model steam engines:



I don't like the sound of 'clapper valve', so I'm describing my version as a 'uniflow', which I believe it is, albeit a simple example of the type. I am taking the basic working concepts and the relative dimensions of the working parts from the book. There, however, the similarity will end - mine will have a very different look, and it will be at least three times the size of the original, which has only a 10 mm bore.

Essentially this engine will be scratch built. I have an overall idea in my mind but I'll let it unfold as the thread progresses rather than set it all out here, particularly as the plan will most likely change as I go along.

I decided to start with the flywheel - or I should say flywheels. I have had these two brass discs in my parts box for some time. They are about 11.5 cm in diameter. Originally I had thought of somehow joining them to make one chunky flywheel, but I have now decided that the engine will have twin flywheels. This, along with my idea for a frame, will have implications for some of the engineering further down the line. For the crankshaft, the bigger of the two pieces of precision ground mild steel is a bit heavier than I would have chosen, but I have it in my shop and I fancy pursuing a 'use what you have' aesthetic as far as possible with this build:



The flywheels will be composite in nature, each having a central boss  made from a separate piece of brass. They will also have a pattern of holes so I had to drill out and bore the centres so that they will fit the small four-jaw chuck which is mounted on my rotary table:



So, a small start has been made.

This will be a fairly chunky engine and it will need a fairly powerful boiler to run it. More of that later...



Offline MJM460

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Re: A Simple Uniflow Engine
« Reply #1 on: April 27, 2020, 01:19:49 PM »
Hi Gary, good to see you building another engine.  I am looking forward to seeing what you will do to put your mark on this one.

The design seems to have much in common with the principles used in a high speed hydroplane which was written up in the magazine.  However that was was a very highly developed performance monster. Yours looks much more reasonable, but who knows where it will lead.

K.N Harris mention the uni flow principle in his book.  You might be interested to know that that is the one that really got me interested in applying thermodynamics (which was central to my working life) to understanding in some detail how this helped understanding our models, and ultimately lead to my Talking Thermodynamics thread.

So not really sitting back, as I seem to be busier than ever these days, but looking forward to following along with your new build.

By the way, how is your flash steam plant going? 

MJM460
The more I learn, the more I find that I still have to learn!

Offline gary.a.ayres

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Re: A Simple Uniflow Engine
« Reply #2 on: April 27, 2020, 10:49:46 PM »
Hi MJM, and thanks.

My hunch  is that if I make a reasonable job of this it will be a fast runner. I have the K.N. Harris book, and yes, the uniflow engines he describes seem to be of more complex designs.

I haven't progressed the flash steam generator for quite some time as I got 'diverted' into building a brake drum forge. I always considered the flash generator to be something of a side project anyway. That said, I have a sense that something of the sort could be well suited to this engine though I have a feeling I'd need a bigger coil, which would be easy enough to do.

However, I also have other plans when it comes to boilers. Not going to say any more about that at the moment as I don't want to jinx it!   ;)

Hope you are doing ok with the challenges of the pandemic. Are you still in lockdown in Australia?

Cheers,

Gary

Offline MJM460

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Re: A Simple Uniflow Engine
« Reply #3 on: April 28, 2020, 08:19:19 AM »
Hi Gary, the engine you are making is very similar in principle to that high speed hydroplane, Pisces, that I mentioned, though yours will be a more appropriately gentle one to tame.  The hydroplane had the principle refined, and the manufacture developed way beyond anything I could imagine doing.

The K.N. Harris design was closer to yours in performance, but added the “uni flow” exhaust ports to a more conventional engine, to get more power output.

Yours will be quite economical on steam as the inlet port will only be open briefly, thus allowing for plenty of work to be developed through expansion.  It will be happier running faster, and the overall performance will be interesting to look forward to.  Most simple engines, the inlet valve is open for longer, so they do admit more steam, then simple exhaust it to atmosphere rather than achieving so much expansion.  In the end it is all about valve port timing and there is a big variation between different designs.

With that design, the inlet port opens before dead centre, so this limits how long it can remain open after dead centre without becoming too difficult to start.  You will need to flick the flywheel, to start it, but t should run well.

I assume you will make provision to collect the exhaust steam, and not just have the port to atmosphere as per Stan’s book.

Looking forward to following your boiler exploits.

Still in lock down here.  Work is acceptable here for those who can’t work from home, but people in our age range are advised to stay home apart from a daily walk, which we are making the most of.  We both have hobbies that we are enjoying being able to spend more time on.  I think my wife misses company much more than I, but we both miss the social aspects of family and friends, but managing well and keeping happy.  Technology is a big help but does not entirely replace human contact, and never will.  The different approaches taken by different countries and even different states are interesting and will provide a quite good data set for the next time.

Time in the workshop is filling in the gaps left by other activities that have to be on hold, so busier than ever.  But no point making face masks at this stage as our medical authorities are not recommending them for general use.  Obviously the jury is still out on that one too, and those who analyse this stuff later will eventually work out which way we should all go.  Or will it depend on which combination of other measures are in place?

So going well here.  I hope you are also managing ok in this world that is so different from what it was less than two months ago.

MJM460
The more I learn, the more I find that I still have to learn!

Offline gary.a.ayres

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Re: A Simple Uniflow Engine
« Reply #4 on: April 29, 2020, 10:09:50 AM »
MJM - I will look for some information on the Pisces engine as I may be able gain some ideas from it.

Thanks for your explanation on anticipated performance - it's encouraging!

On the exhaust ports - yes, my plan is to collect the exhaust steam and route it to wherever. Stan Bray advises that if his design is scaled up, extra ports should be drilled rather than enlarging the single one in his version, so that's what I'll do. My thought is to make a manifold to gather the exhaust from the ports and direct it into a single pipe. Could look pretty cool too if I make a decent job of it. That feels aeons away at this point though!

The lockdown where I am has been partly eased, i.e. tradesmen who work outdoors are now back at work provided they socially distance. Otherwuse it's still the same - one walk a day, and so on. I live on an island which has managed the situation pretty well and the curve here has been pretty much flattened. They are doing much better here than they are in the UK mainland (where my daughter works as a nurse...), and I think they will ease the lockdown carefully, measuring as they go.

I'm lucky in terms of the work side of things. As a psychotherapist in independent practice my business took a bit of an initial hit, but it has picked up again in virtual form so I'm actually quite busy. My partner is a teacher and she is working from home, setting work for her students online. Not everyone is so fortunate though.

Taking a day off today to spend some time in the shop though!

Great that you are able to do the same. What are you working on?

 :ThumbsUp:

Offline gary.a.ayres

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Re: A Simple Uniflow Engine
« Reply #5 on: April 30, 2020, 12:09:32 AM »
A bit of progress today in the form of drilling holes in the two flywheels and turning one of the bosses.

The flywheel blanks are just brass discs (albeit quite thick ones) so they need to be fitted with a boss each so that they can be secured to the shaft. I only had a small piece of brass bar in my box so I didn't have the luxury of extra length to hold with the chuck. The solution was to use a 'superglue arbour', which was an idea that I first came across on Clickspring's youtube channel. This was the first time I have tried it and it worked really well. I cut the piece of bar into two with a parting tool and hacksaw to make the blanks for the bosses, cleaned them up and faced them and then drilled and reamed them to make a sliding fit on the shaft. I then found a piece of spare round bar in the scrap box which was slightly oversized for the hole so I turned it down to size and then fixed one of the boss blanks to it with superglue. This made easy work of what what would have been a problematic turning operation:



Once the job was done, a bit of heat from a small blowlamp destroyed the superglue, allowing the workpiece to be removed from the arbour. Prior to this I had drilled a circle of five holes in each of the flywheel blanks. These were marked out on the rotary table with dividing plate and finished on the drill press. I thought I'd try a five hole pattern as it perhaps has a more dynamic feel to it than six does. I may enlarge these holes a bit later on - it depends how it looks when the engine starts to take shape. These will be very minimal flywheels - no recess, etc. The interest will lie in the fact that there will be two of them. Here they are at the end of today along with the boss that I made:



It got quite late so I left the second boss set up with superglue arbour no. 2, ready for turning tomorrow evening. Here is the state of play so far, with the boss trial-fitted to one of the flywheels and mounted on the shaft:



The bosses will be cross-drilled and threaded for grub screws then loctited into the flywheels.

gary






Offline MJM460

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Re: A Simple Uniflow Engine
« Reply #6 on: April 30, 2020, 01:40:36 AM »
Hi Gary, great progress on those flywheels, and it sounds like you have the exhaust arrangements sorted.

The different approaches to lockdown are interesting.  Our outdoor workers have continued through, though there is some grumbling on large construction sites about people not modifying procedures to institute social distancing.  Yet we have not just flattened the curve, but got it right down.  New Zealand had a more severe lockdown, and had a similar result.  I believe Italy and Spain might have much more severe lockdowns and still struggling.  It is becoming clear that “go hard, go early” is the critical component of the strategy, to get it under control before it is established in the community.   Along with lots of testing.  Some countries seem to have low totals, but are not testing anyone, some only count hospital cases, so it is really hard to compare different results.

But one thing that is very clear, the community and the media are both very black and white, with very little understanding of uncertainty and probability, and some understanding of both is critical in this sort of situation.

Glad you and your family are ok, being on an island with early lockdown is a huge advantage.

I am busier than ever with the combination of adapting to new ways of doing everything, which just shows how much energy our brain uses and why we quickly learn to do things on automatic.

Working on two projects, one ready for some tidying up of my notes (and coming soon to a forum near you, and the other just starting, along with iPad brackets for the camera tripod for zoom meetings and similar new requirements.

Keep sheltering keep happy and keep busy,

MJM460

The more I learn, the more I find that I still have to learn!

Offline gary.a.ayres

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Re: A Simple Uniflow Engine
« Reply #7 on: April 30, 2020, 01:04:33 PM »
Thanks for the encouragement, MJM.

Yes, strict and early lockdown seems to be the winning formula. They were a little bit slow on lockdown on this island but not so slow that they couldn't get on top of it. The mainland UK, on the other hand, have been outrageously slow, and the consequences speak for themselves.

Agreed - coming off auto-pilot is tricky and time-consuming. It would be nice to think that it won't be long before we have to do it again in the reverse direction.

Good to know that you are working on projects. Any chance you could give me a heads up when you post the forum thread?

Offline gary.a.ayres

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Re: A Simple Uniflow Engine
« Reply #8 on: May 01, 2020, 01:08:16 AM »
This evening's efforts:
 
I made the second flywheel boss, and drilled and tapped (M6) the holes for the grub screws that will secure the flywheels to the shaft:





The bosses are not a tight fit in the main parts of the flywheels, so I used a generous amount of Loctite 638 to fix them in place:





If the rotational force of the flywheels appears likely to weaken the Loctite when in use and shear the bosses from the wheels, I'll have the option of putting a circle of small screws through the flange of each pulley into the wheels to secure them. I suspect that this won't be necessary though.

Offline MJM460

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Re: A Simple Uniflow Engine
« Reply #9 on: May 01, 2020, 01:53:57 AM »
Hi Gary, good progress on those flywheels.

Your engine, by the nature of its valve operation, will tend to have a quite impulsive torque pattern rather than the smoother sine wave of a more conventional valve operation.  That will tend to stress the shear strength of your loctite connection.

And somewhat counter-intuitively, that loctite connection is near the section of the flywheel with the highest shear stress to transmit that torque.

A simple option would be to drill through the flange and wheel as you have suggested, but just insert good fitting pins, just loose enough to leave some room for the loctite, and loctite them in and file or machine flush when the loctite is set.

These pins will transfer the torque in shear, so you will be using the shear strength of the metal pins instead of the shear strength of the loctite, and the loctite only has to stop things falling off.  Easier to do than screws and tapping threads.

I know many people seem to have good experience with using loctite as glue, so it may be enough, but hard to confirm on theory alone.  The strength requires testing, as do so many theoretical issues, and so much will depend on how well you do the loctite joints with clearance, temperature, cleanliness etc.  The pins will be a better solution, and easier to fit than screws.

No problem on the heads up, but I don’t have your email address.  I believe there are forum settings that cause the forum to send you notifications, so if you check those, you will get notice in your email.  But it is not far off, so if you remember to notice any little message flags when you check in to do your posts, I will send you a pm.  I don’t think you get the message flags though, unless you sign in.  Unless I find your email visible in your profile.  I need to check that again too!

Keep up the good progress.

MJM460
The more I learn, the more I find that I still have to learn!

Offline steam guy willy

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Re: A Simple Uniflow Engine
« Reply #10 on: May 01, 2020, 02:18:05 AM »
Hi Gary , further to MJM's post I have used Sellick pins with good results...these are sometimes called roll pins and is a sort of sprung type of pin you can get them in lots of small sizes...good work going on here :)

Willy
« Last Edit: May 01, 2020, 02:49:00 AM by steam guy willy »

Offline gary.a.ayres

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Re: A Simple Uniflow Engine
« Reply #11 on: May 02, 2020, 01:28:39 PM »
Hi Both -

Well, I'm not here to ignore good advice. I haven't used Loctite many times but on the occasions that I have I've been amazed by its performance. That may actually have led me to wrongly believe that anything can be achieved with it, even though aesthetically in an ideal world I'd probably prefer not to use glue in engines at all. Rather than wait for things to go wrong and fix them later, I'll go with what you suggest and do a proper job now.

MJM - it is actually quite intuitive to me that the shearing torque will be higher nearer the centre and that the stress on the join between the bosses and the wheels will be high. I remember feeling sick on playground roundabouts as a kid and realising that if you had any chance at all of stopping it by putting your feet down it would be at the outside edge, not in the middle. In the present case, all the more so if the engine is a bit of a jerky runner. Tapping some holes wouldn't be a problem but I think I prefer your pins suggestion so I'll go with that. There would be something phoney about having screws that aren't actually acting as screws, after all. Pins will be more 'honest'.

SGW - I have seen that kind of pin before, when I dismantled an old car engine for fun and to get parts from to use in projects. They are really good and I can see that they would do the job very well. However, as I don't have any of them but do have some thin round silver steel bar, I'll use short lengths of that Loctited in as MJM suggests.

Thanks for your input, both.

 :ThumbsUp:

Offline gary.a.ayres

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Re: A Simple Uniflow Engine
« Reply #12 on: May 05, 2020, 11:03:14 PM »
I decided to make five holes through the boss and main body of each wheel to correspond with the five 'decorative' holes in the flywheels. To do this I mounted each flywheel in the small 4-jaw on the rotary table in the mill. I just used the setup as a circular vice, eyeballing the positions of the small holes, centre drilling then drilling them, and rotating the wheel by hand each time. I did it this way because I had to drill right through the wheel and If I had rotated the table I'd have fouled the chuck jaws with the drill.





The drill I used was chosen to allow an easy push fit of a spare piece of silver steel which I had in the shop:



I cut the pins from the silver steel and then ground them roughly to length - or a little over - on the bench grinder, holding them in this vintage hand vice. I bought this vice in a second-hand emporium in Brighton while visiting my daughter there about a year ago. At the time I wondered if I would ever use it, and indeed I haven't used it a great deal but there are odd occasions like this where I wouldn't be without it:



The pins in their rough form were fixed into the holes using Loctite 638...



... and then the bosses were faced in the lathe:



You will see from this last photo that there is still a lot of work in finishing these flywheels, with machining and chatter marks to face and polish out. However, the pinning operation completes them in their basic form, and overall I'm quite pleased with them. Much of the finishing will be done in situ on the crankshaft.

Meanwhile, I have been in planning mode, ordering some new tooling and making a list of materials that I'll need to continue with building the engine...

Offline Jasonb

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Re: A Simple Uniflow Engine
« Reply #13 on: May 06, 2020, 07:16:30 AM »
I'd have just stuck with the loctite unless your fit was really loose, plenty on here have made engines with bigger flywheels loctited together, often on crankshafts that also use loctite to make up the crankshafts or hold a crank disk to the shaft, in both cases the glue area is far smaller and stresses far higher
« Last Edit: May 06, 2020, 08:01:46 AM by Jasonb »

Offline Zephyrin

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Re: A Simple Uniflow Engine
« Reply #14 on: May 06, 2020, 08:12:37 AM »
The annoying thing with these machining marks is that they tend to recur and even amplify on reworking.
you really have to change radically the machining routine, I suggest a very wide tool 10-12 mm and an ultra-slow speed, even turning by hand!

have fun with this new model!