Author Topic: A Simple Uniflow Engine  (Read 7672 times)

Offline Jasonb

  • Full Member
  • *****
  • Posts: 7512
  • Surrey, UK
Re: A Simple Uniflow Engine
« Reply #30 on: May 15, 2020, 07:23:42 AM »
What do you intend to assemble the crankshaft with?

Put an internal fillet on those side projections to reduce possibility of stress fracture and just so it looks nice.

Never a fan of big boxy big ends as there is a lot of unbalanced weight flying around so some shaping would not go amiss

I've only used CI as a bearing in slow speed applications so can't give first hand on running it fast.

Offline gary.a.ayres

  • Full Member
  • ****
  • Posts: 878
  • British Isles & sometimes France
Re: A Simple Uniflow Engine
« Reply #31 on: May 15, 2020, 09:27:25 AM »
Jason -

Regarding the speed issue - thanks. I will do a bit more research and of course other forum members may have views too. If I don't hear anything to say that I shouldn't keep the bearing in cast iron, I'll give it a try as worst case scenario it could always be modified later with a bronze bush if it fails.

Great idea about the internal fillet.

Agreed re the boxiness, and good point re the unbalanced weight. The rectangular shape in the sketch is just a starting point really. For example, there is much more cast iron below the split than there is above it, so I'll be reducing the size below the split. Some kind of tapering on the bottom part might look good, and some rounding of the top part too. I reckon on starting with regtangular to the point at which it's functional, then do some shaping to finish.

For the crankshaft I have 12mm silver steel, and was thinking about using rectangular section EN3B for the webs. That said I have some 3/4" square EN1A which could be nice for the webs in terms of the look, though on reflection that might be too narrow. I wonder if you or anyone else have any thoughts about these materials. As it's my first proper crankshaft I'll probably not go for a press fit, so Loctite it will be, possibly with pins (I know you said previously that pins shouldn't be necessary, but this will be a fast runner and I like to know that things are rock solid).

Thanks once again, and have a good day.

 :ThumbsUp:


Offline Jasonb

  • Full Member
  • *****
  • Posts: 7512
  • Surrey, UK
Re: A Simple Uniflow Engine
« Reply #32 on: May 15, 2020, 01:24:03 PM »
EN£ and silversteel will be fine, as you won't be soldering then you can harden and temper the pin Ok though you could get away with leaving it as supplied.

Offline gary.a.ayres

  • Full Member
  • ****
  • Posts: 878
  • British Isles & sometimes France
Re: A Simple Uniflow Engine
« Reply #33 on: May 15, 2020, 01:32:39 PM »
Jason -

by EN£ (possibly a typo) do you mean that EN3B will be fine, or that either of the EN steels I mentioned would be fine?

I did consider silver soldering the crankshaft together. It would be more pleasing to me to do that than to Loctite it. However, my concern would be whether that could risk distorting it with the heat. Do you have any thoughts on that?

Thanks for your interest,

gary

Offline Alyn Foundry

  • Full Member
  • ****
  • Posts: 1150
  • North Wales, Great Britain.
Re: A Simple Uniflow Engine
« Reply #34 on: May 15, 2020, 01:51:56 PM »
Hi Gary.

You don't have to worry about cast Iron bearing to Silver Steel crankshaft....


My Robinson is 31 years old and has run 1000's of hours. Nary a sign of wear in either of the " mating " surfaces. The engine can run up to 500 RPM too.

I prefer Silver soldered cranks too.... ;)



Cheers Graham.

Offline Jasonb

  • Full Member
  • *****
  • Posts: 7512
  • Surrey, UK
Re: A Simple Uniflow Engine
« Reply #35 on: May 15, 2020, 04:24:25 PM »
What sort of speed are you hoping for, I got the impression you were after a bit of a goer with flash steam?

EN3B will be fine for the webs. Reason for asking about assembly method is that you can't really have a hardened pin and silver soldered joints as you want the assembled crankshaft to cool slowly which will not harden the pin. For slower speeds you don't really need to think about hardening.

Offline gary.a.ayres

  • Full Member
  • ****
  • Posts: 878
  • British Isles & sometimes France
Re: A Simple Uniflow Engine
« Reply #36 on: May 15, 2020, 04:31:31 PM »
Thanks Graham.

What a great-looking engine! That big end bearing looks to be pretty much what I have in mind. Most encouraging...  :ThumbsUp:

In the book I cited earlier, Alex Weiss says:

'Because of its in-built graphite content, cast iron is an excellent bearing material. In use with a steel shaft, the surface of the cast iron gains a tough glazed surface that is very wear-resistant. An additional advantage is that cast iron bearings will continue to operate satisfactorily even in conditions of poor lubrication, though this is no excuse for failing to provide an adequate supply. A relatively unique property of the material is its ability to be used in conjunction with itself. Thus, the cast iron slides of machine tools may rub against cast iron mountings or gib strips of the same material.'

I'm definitely going to give it a go, and am looking forward to machining the bearing. Exciting!

Thanks also for the link to your video of silver soldering a crankshaft. I will definitely not rule that out, and look forward to watching the video - which I will do later this evening. Expect a couple of new comments on your youtube channel...  :)

Out for a walk in the sunshine now, though.

Cheers,

Gary

Offline gary.a.ayres

  • Full Member
  • ****
  • Posts: 878
  • British Isles & sometimes France
Re: A Simple Uniflow Engine
« Reply #37 on: May 15, 2020, 04:38:25 PM »
What sort of speed are you hoping for, I got the impression you were after a bit of a goer with flash steam?

EN3B will be fine for the webs. Reason for asking about assembly method is that you can't really have a hardened pin and silver soldered joints as you want the assembled crankshaft to cool slowly which will not harden the pin. For slower speeds you don't really need to think about hardening.

The speed: tbh Jason I don't really know. I may in due course run the engine on flash steam when eventually I get my flash steam boiler done, but prior to that I may run it on something else. Speed per se isn't the issue for me - I was just attracted to the design, mainly because of its simplicity for a beginner like me. However, I am given to understand that it will prefer higher speeds, so I'll just wait and see what emerges.  :)

EN3B: good to know, thanks.

Thanks for your advice about the crankshaft. Noted. I may yet use silver solder. Graham's video - which I will watch later - may help me make up my mind. I'll either be inspired or intimidated... and probably a bit of both! But nothing ventured, nothing gained...

Cheers,

gary

Offline Alyn Foundry

  • Full Member
  • ****
  • Posts: 1150
  • North Wales, Great Britain.
Re: A Simple Uniflow Engine
« Reply #38 on: May 16, 2020, 03:20:45 PM »
Hi Gary.

Thanks for your comments on my YouTube channel....  ;)

The Robinson replica is 1 1/2" bore and 2" stroke.

The crankshaft is first centre spotted at both ends. If you noticed we started heating the main shaft from both ends, effectively " stretching " the metal evenly. Then you start increasing the heat where the joints are. We apply,  liberally the flux. Having tried many over the years I can totally recommend Tenacity number 5 for this job. Specifically designed for Silver soldering Ferrous materials.

We cut small sections of the Silver solder and put them at each joint. You probably noticed that one dropped away so sometimes you have to manually apply a little more.

Once cold the " bridge " is cut out and the whole assembly put into an Acetic acid bath for 24 hours to remove the flux residue.

Because of the " spotting " you can now " true up " any discrepancies in the lathe.

Just for fun....


Cheers Graham.

Offline gary.a.ayres

  • Full Member
  • ****
  • Posts: 878
  • British Isles & sometimes France
Re: A Simple Uniflow Engine
« Reply #39 on: May 17, 2020, 09:54:48 AM »
Graham -

Many thanks for your detailed description of how to silver solder the crankshaft.

I'll give some thought to the question of siver soldering mine vs using Loctite.

As you don't mention pins, I presume you don't use any.

That Robinson is a beauty!

Cheers,

Gary

Offline Alyn Foundry

  • Full Member
  • ****
  • Posts: 1150
  • North Wales, Great Britain.
Re: A Simple Uniflow Engine
« Reply #40 on: May 17, 2020, 11:37:10 AM »
Graham -

As you don't mention pins, I presume you don't use any.

That Robinson is a beauty!

Cheers,

Gary

No pins Gary.    :)

Offline gary.a.ayres

  • Full Member
  • ****
  • Posts: 878
  • British Isles & sometimes France
Re: A Simple Uniflow Engine
« Reply #41 on: May 17, 2020, 12:47:04 PM »
Cheers Graham.

 :ThumbsUp:

Offline Jasonb

  • Full Member
  • *****
  • Posts: 7512
  • Surrey, UK
Re: A Simple Uniflow Engine
« Reply #42 on: May 17, 2020, 01:09:37 PM »
And just when you thought you had decided what way to do it someone comes along and says they use pins as they like to apply the solder to one side of the joint only it makes it a bit hard to tell how deeply it has flowed.

http://www.modelenginemaker.com/index.php/topic,2160.msg39156.html#msg39156

Offline gary.a.ayres

  • Full Member
  • ****
  • Posts: 878
  • British Isles & sometimes France
Re: A Simple Uniflow Engine
« Reply #43 on: May 17, 2020, 01:29:35 PM »
Right! That's it! I'm going back to stamp collecting...  >:(


Thanks Jason. Great post and pictures, which will be an excellent resource for me if I decide to use silver solder.

Your Galloway thread as a whole will be worth reading, I have no doubt. I have kept the tab open for later... :popcorn:

Hope you are having a good weekend.

gary

 :ThumbsUp:


Offline MJM460

  • Full Member
  • ****
  • Posts: 1224
  • Melbourne, Australia
Re: A Simple Uniflow Engine
« Reply #44 on: May 17, 2020, 01:54:41 PM »
Hi Gary, while you are thinking about silver soldering, I will make a few comments on the overall project.

It is important to separate the ideas of flash steam and high speed engines.  Of course, the two are often associated in a project, and for quite valid reasons, but it is not necessarily so.

A flash steam boiler, sometimes called a mono tube boiler, is a boiler configuration that provides a quite  large heat transfer area for steam raising, with quite low weight for the steam production achieved.  But at the end of the day, the amount of steam raised is determined mostly by the burner, and how much fuel can be burned, so long as you have enough heat transfer area.  I was tempted to include the word efficiently in that sentence, but not all projects are interested in efficiency.  If someone wants to break a record, they want maximum power, and if burning more fuel, even less efficiently, achieves more power, then they go for it.

Part of the low weight is achieved at the expense of water capacity.  There is effectively no water storage in a flash boiler, so they canít be operated like my little boilers by filling up with water then lighting the burner and start steam production.  Well perhaps they could, but it would be a quite short run.  They really need a feed pump, preferably driven by the engine, but again it is not the only way.  The preference is because both steam consumption and water requirement, the same thing really, are dependent on engine speed, so while it is still not easy to balance the two, it is easier than if a separate pump is used.

Of course, the high power to weight ratio is very desirable for high speed vehicles, whether land based or water, and when combined with a very big burner, can produce awesome power to drive the engine.

But it does not have to be so.  If you use a quite moderate burner then you produce only the proportionate amount of steam.  You could build a quite moderate steam plant for a model boat for very sedate performance.  This approach has its own chapter in Benson and Raymanís excellent book, even though the rest of the book is a fascinating look into the world of high speed hydroplanes.  I think I remember you buying it, so you will be aware of the valuable information there.

In addition, it is not necessary for there to be no water storage.  A moderate plant can include a pressurised water tank, with an air cushion over the water, between the water pump and the steam coil.  It will smooth out the flow and give a bit of a safety factor against water failures, which might allow you to bring a model back to extinguish the burner.  A separate tank like this can allow design of the plant with a much lower centre of gravity than a more conventional boiler design, which is good for stability of a model boat.  Of course the fire tube marine boiler also has a good low centre of gravity.

The engine is a quite separate issue.  An oscillating engine as you have already built can operate quite slowly when required, particularly a twin cylinder double acting design which does not have the dead spots that the flywheel must supply the energy to carry through.  Similarly a slide valve engine, or any of the other designs we usually see on this site.  The upper speeds are mostly limited by the quality of balancing achieved, not easy with heavy reciprocating parts.  My mill engine achieves around 2000 rpm unloaded with quite low steam pressure, with limited balancing, but I suspect that even at this speed, wear might become an issue if I pushed it that fast for long.  So hardened pins and more attention to bearings might be required.

Slow engines are generally characterised by long stroke compared with the bore, though not necessarily so.  More significantly the steam is admitted mostly after the top dead centre, even when a little is admitted before.  Your engine with the inlet valve operated by a peg on top of the cylinder has the steam admitted equally each side of top dead centre. (I wonder how a double acting engine would be implemented).  More likely a twin single acting, or better still a three or more cylinder configuration with the cranks spaced equally around the shaft.  Because of this necessarily early admission, the engine needs to get enough of a kick every steam admission to accelerate the flywheel to store the energy necessary to push the piston over the next top dead centre position.  Otherwise the engine might just oscillate back and forth through about 340 - 350 degrees.  The engine will be happier going faster for this reason, but it still does not require the extreme speed sought by the racing community, it just wonít run slowly like your little oscillator.  But a quite interesting design, well worth trying.

So while roaring blowlamps, extreme pressure and temperature steam conditions, and high speed racing hydroplanes, are typically based of a flash boiler, uniflow engines, and very highly developed material selection, and manufacturing techniques, there is no reason why you cannot run your simple flash plant with a more moderate burner and your current engine, which might run quite happily around 1500 - 2500 rpm (at a wild guess) but definitely not slow like your oscillator.  Mind you, an oscillator is also is no slouch if you give it enough steam, as the oscillating engine design involves a much smaller oscillating mass than a typical mill engine, in both reciprocating and rotary motions.  Mine go at 2000 rpm measured with a digital tacho when unrestrained and with only the little meths burner, and are really not fussed at this speed.  Much less vibration than the mill engine.

It is one of those things that has to be tried, but if you can tackle a little engine driven pump, perhaps with bought gears, there is no reason that you could not try your flash plant with this new engine.  Keep the burner relatively gentle until you get the feel of it.  But I really would not recommend the flash plant with a hand pump only, unless you have plenty of water capacity.  It all comes back to heat balance.

By the way, stamp collecting is only allowed during the current lockdown situation, and there is another current thread where that can be included.  In the mean time you have an an engine and flash boiler to complete!

MJM460

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