building the triple expansion engine in M.E.

Hi guys.

I am confused again ( no surprise there then)

I fancied having a go at this engine and I thought the crankshaft looks the most complicated bit so if I can do that the rest should be reasonably easier,

BUT, I can't get my head round how the ends are marked out.

Am I to assume that there are 10 centres marked on each end?

3 for the cranks, 6 for the cams and 1 for the centre.

I laid it out on a piece of paper and it looks awfully crowded.

Any help and guidance is appreciated.

Cheers

Roy

Thats it.

As shown there is only one set of cam centres but you will end up with six equally spaced around a 4mm dia circle.

Certainly a case for the smallest ctr drill you have!!

Thanks for that Jason, the other challenge seems to be making sure you use the correct centres so the right cams go with the right crank.

Could be fun

I can't figure out which of the two centres for each cam relates to the position of the cam on the shaft.

get that wrong and you have two cylinders going forward and one going in reverse.

Cheers

Roy

It wants drawing out a few times larger than actual size. And then make a note of which way will be forwards then say make all the cams that are forward of the crank the nearest the web and all those reverse the furthest from the web.

As all the valve chests are on teh same side of the cylinders so long as you use the same relationship for each pair it won't matter which is forward and which reverse.

If you are not sure I'll sketch it out

.

Cheers, that makes sense.

A sketch would be helpful if it's not too much trouble.

Roy

Off into the shed now but will do it later.

J

Hi!

I make a drwing for you, hope it help.

Regards

Gunnar

Thanks, it's all becoming clearer now.

Roy

I don't think Morgens made it very clear how /why the eccentrics are set out the way they are.

Neil

Hi There

Three crankpins as shown on the drawing.

So, at 120 degrees apart.

Eccentrics at 90 degrees to the crankpin, one each side.

Simples.

regards David

Well Gunnars sketch shows how each pair relates to the crank but there is still a chance of getting the forward & reverse eccentrics transposed. Hopefully this will show you how each of the six eccentric centres relates to the position along the crank.  As I have drawn it my reversing lever will be the opposite way round to Morgens but as I said so long as all three pairs of eccentrics are consistant it makes no difference as there is no lead or lag to the eccentrics. Click to enlarge.

Note the drawing of the right hand pair of eccentrics in the mag is wrong, I susspected it earlier but now I have drawn it out it is definately wrong. The amount of throw shown should be the same for middle and R/H not larger on the R/H crank.

J

Edited By JasonB on 01/06/2012 20:54:30

Thanks for that Jason, by jove I think I've got it.

cheers

Roy

I've altered it to be timed like Morgens, will stick up the pic in the morning.

Reveised drawing below for those that want it timed as per Morgens.

Thanks Jason, I'll print that and study it.

cheers

Roy

90 degrees might be the easy way to place the eccentrics, but surely not the best?

Neil

I did mention about them having no lead but on such a small engine I doubt its worth worrying about.

I'll leave you to do the drawing with say 7.5 degree lead

J

i am not familiar with this design, but surely with stephensons gear with launch type links and nil lead in full gear, the amount of advance on the eccentrics = lap on the valves, measured by axial distance as opposed to in degrees. its then quite a simple matter to work out the angle of advance. if the eccentrics were at 90 degrees to the cranks that would be quite wrong if there was lap on the valves... which i am sure there is! if the design is with cams and poppet valves the same principle applies?

cheers,

julian

Edited By julian atkins on 07/06/2012 12:46:42

Why are you sure?

Do they have lap on piston valves?

regards David

dave,

for any form of expansive working slide valves and piston valves need lap, otherwise the steam continues to enter the cylinder right up to the exhaust/release point

cheers,

julian