Thread: Straight four Engine design.

Originally Posted by Ueee

Now where is Phil, i'm sure he will have a tip or 2 now you have put the word steam in there.....

Ew

Hi Ewan,
I tried very hard to keep out
I just can't sit out any longer. The best crank manufacture I have seen is the piece of flat bar, approximately 3"wide x 1.5" thick and however long, then cut part way through, heated up with the oxy and twisted to form the counterweights and journals.
It was thrown in the lathe and machined up.
For the 'nay sayers', the twisted sections were then x rayed and were found to be faultless.
With regard to crank positions, they change for compound, cross compound, quadruple expansion simple expansion etc. Even one high pressure cylinder, two intermediate and one low pressure is different again.
It's a minefield of combinations
Any thoughts on the configuration you are after BaronJ?

Phil

Originally Posted by Steamwhisperer

flat bar, approximately 3"wide x 1.5" thick and however long, then cut part way through, heated up with the oxy and twisted to form the counterweights and journals.

Sorry Phil, I'm going to need a little help with that.... Understanding your description I mean.

Originally Posted by Bryan

Sorry Phil, I'm going to need a little help with that.... Understanding your description I mean.

I'll see if I can find the article Bryan

Phil

Originally Posted by scottyd

How badly does it need to be one piece? You would only go to such significant lengths if the motor was expected to output a lot of torque. Id consider making it in a number of parts and fitting them together. Also means that if you cock one bit up, youre not binning a large, expensive billet.

Hi Scottyd,
I hadn't given any thought to using individual parts, but I do take your point. The size of billet would be dictated by the crank throw and number of bearing surfaces. I had thoughts of something like a 20mm crank throw to give a 40mm stroke, using 10mm journals.

Originally Posted by Ueee

There was the pics of the boat building workshop someone linked to a few months back, they shrank fit the offsets/counterweights onto the bar for the mains and big ends. We were talking massive scale though...

Now where is Phil, i'm sure he will have a tip or 2 now you have put the word steam in there.....

Ew

Edit, here is that thread, https://www.woodworkforums.com/f65/in...g-look-176644/

Hi Ueee,
Yes I remember looking at that. That crank is a little bigger than I would want to make !!

Originally Posted by Steamwhisperer

Hi Ewan,
I tried very hard to keep out
I just can't sit out any longer. The best crank manufacture I have seen is the piece of flat bar, approximately 3"wide x 1.5" thick and however long, then cut part way through, heated up with the oxy and twisted to form the counterweights and journals.
It was thrown in the lathe and machined up.
For the 'nay sayers', the twisted sections were then x rayed and were found to be faultless.
With regard to crank positions, they change for compound, cross compound, quadruple expansion simple expansion etc. Even one high pressure cylinder, two intermediate and one low pressure is different again.
It's a minefield of combinations
Any thoughts on the configuration you are after BaronJ?

Phil

Hi Phil, & all,
At the moment its just thoughts and scribbled bits of paper. I took the view that getting the crank design right was probably the key to the whole engine. Which since I had already decided that I wanted four cylinders, things like journal sizes would be important as would crank throw since this would dictate stroke length. The next thoughts were how I was going to create such a crank. So far I haven't given much consideration to most of the things you mention. I've looked at quite a number of engines and freely available plans which are quite confusing. So I looked around for information on principles. Not finding anything useful about four cylinder engines I thought this was the place to ask. The only real experience I've had with engines has been with the various cars I've owned over the years. Now I've retired, built the XYL a new kitchen, (I did promise for Christmas, with two days to spare.) I'm hoping that I can find time to do some engineering.

Double or single acting pistons? Going to employ a piston rod or go straight to a conrod? I like phils idea of staged pressure levels from one piston to the next, would make for an efficient engine.

Originally Posted by scottyd

Double or single acting pistons? Going to employ a piston rod or go straight to a conrod? I like phils idea of staged pressure levels from one piston to the next, would make for an efficient engine.

Hi Scottyd, n all,

I haven't really enough knowledge at the moment to understand staged pressure levels. I'm leaning towards double acting. Some bits I've read suggest that slide valves are better than piston valves others say the other way round. I like the way a railway engine has the valve gear on the side of the cylinder but I don't know if stacking four of them side by side would be practical. It was the realisation that the pistons on one side were 180 degrees from each other that prompted the original question.

Hello BaronJ,
Twin cylinder loco cranks will not be at exactly 180 degrees, as this creates a "dead point" where both cylinders can stop at top or bottom of stroke and not be able to re-start. May be OK for a small model that you can flick over to get it going, but not so good with a few thousand tons of dead weight behind. Believe Stephenson's Rocket needed a push start on occasions.
Twisting a hot forging to form crank throws is a time honoured process. Rob Laurent's definitive book on Toowoomba Foundry, (Southern Cross) shows the workers with a glowing billet on the bench and two guys with a long clevis bar twisting it to form a 3 cylinder crank in the 1960's I think. Many early steam engines had cranks hot formed from lengths of round shaft. On a small scale it may be easier to notch out a flat bar and machine the journals in a lathe. Good luck with the project. Combustor.
PS, two double acting cylinders gives four powerstrokes per revolution, whic would need 6 cylinders to achieve in a fourstroke IC engine.

Too late at night, brain not in gear. Last line should read "8 cylinders!" Combustor.

Hi Combustor,

I know what you meant. Thanks for the description of the way cranks were made.

All,
I've been doing some more research and found some very interesting information on the evolution of stationary steam engines. Particularly with regard to valves and valve gear. I found an informative web site discussing "Corliss Engines" and the development of the rotary valve as used in these engines.

<http://wkinsler.com/technology/corliss/figures/index.html> and <http://wkinsler.com/technology/corliss/index.html>

I still need to learn a lot more than I do now ! So I have decided to build a model of a single cylinder, before diving into the pool at the shallow end.

Hi BaronJ,
doing a single cylinder is a great place to start and you will learn heaps from it. It will make the rest of this minefield of engine configurations easier to understand as well.
Valve gear is another mine field as there is a vast array of that as well. Gooch, Woolf, Stephenson link (well his foreman invented that one but he took all the kudos for it), Walschaerts, Joy, just to name a few.
Of course to reverse your engine you could just use the slip eccentric method.
If I was you I would make it non reversing. Hell, I would probably do that if I was 'me'
With a non-reversing engine you then have the direction to think about. Engines will run under the headings of 'running over' or 'running under'. Basically, you stand at the cylinder and looked down the engine, imagine if you were to grab the flywheel while the engine was running, If you got pulled over the top of the flywheel it is running over and if you got pulled under the flywheel it is running under.
If an engine is running over there will be less wear and tear on the crosshead and she will run heaps quieter.
You have piqued my interest here. I reckon you will have a lot of fun on this project.

Phil

Phil,
You intrigue me with the terms 'Running Over' and 'Running Under'.
Do these terms only apply to a single acting steam engine ?
Surely it depends which end of the crank the flywheel is fitted and which side of the engine you are standing when you grab the flywheel.

Presumably, for a double acting vertical engine, these terms (or terms like them) try to differentiate between the crosshead pushing down with gravity and reacting against the linear slides on one side, versus the situation with the crosshead being pulled up against gravity and reacting against the other side of the linear slides.
For a single acting engine, the up motion would actually be a push from the flywheel inertia.

Large non-reversing engines appear to be asymmetrical in cross-section because of factors like this.

I would suggest the OP search for forums that deal with steam engines to a greater extent than we do here.

I hope you clarify the position at work, we all enjoy the contributions you make to the forum.
John