Post by classicsteve on Sept 13, 2009 10:27:03 GMT
Time for the cylinder on my S&P beam engine model. Like so many things on this model, the drawings are significantly modified from the prototype and I am trying to see if I can get closer.
There is no cylinder casting, instead the model drawings suggest turning the cylinder then silver soldering on the valve face. This in turn has required a thick flange on the cylinder base for the steam passage and as a result the base and head threads have to be tapped into the cylinder, rather than being through bolted.
I have measured up the unmachined bronze for the cylinder and it seems there is enough metal to make the whole thing from solid, and I am kicking around ideas of doing this using my rotary table and mill.
So I thought I would ask if others have tried this, or is there some unseen problem. Certainly the 2-part cylinder didn't take advantage of its design to machine any of the steam passages, and I would have thought this is the main issue in making from solid.
It is possible to solder on a couple of smaller blocks in the area where the steam passages need to go, that way the main cylinder can be completely turned and the flanges taken right upto the outer wall of the cylinder. You could also solder on the two end flanges to keep the size of the stock down.
I'm sure Tel will chip in with a few pics of his cylinder fabrications or you may find them in his threads.
If you did solder on the passage blocks it would be possible to pre mill a groove on the curved surface that mates to the cylinder with matching stopped groves either side of the valve block. You would then only need to drill through from the end of the cylinder into these passages once its all soldered up.
I can't see any reason why you can't machine it all from a solid block except for time and you will be using a larger amount of metal with the cost implications
Would the cylinder covers have been bolts and nuts, I would have thought studs into the flange with nuts & washers to hold the covers more likely Jason
Post by classicsteve on Sept 13, 2009 16:57:17 GMT
You are right about the through bolting. I have rechecked my photos of the original. At the top of the cylinder the wall is thicker and the cylinder head goes down onto studs. The bottom of the cylinder doesn't have this - and presumably studs are fitted in the base casting so the cylinder can be lowered onto them.
The way the model is arranged you could never have in real life. As you would have to turn the entire beam engine and plinth upside down to take the cylinder off !
I certainly fancy trying a cylinder from solid - I have wondered about it for some time, but never had a rotary table to try it.
I've recently upgraded from a small 4" Rotary Table that I've had for a number of years to one of the 6" Soba ones that Chronos do complete with dividing plates & centre. I also got a 3-jaw to go with it and its really nice to use, just done the cross head & con rod for my 2" Fowler TE with it, would have been almost impossible without.
Post by classicsteve on Sept 13, 2009 22:55:30 GMT
Woops - sorry - Yes I see in my post I referred to it as the S&P beam engine - it is the Stothert and Pitt beam engine. A Cotswold Heritage kit and drawings came my way at the right price, and the original is in Bath University (www.geograph.org.uk/photo/1186982)
The drawings refer to the model and not to the original engine - which is a shame. There are significant differences - for example the table is a solid lump in the model, but an open framework in the original.
One of the curious things that appears faithful to the original is that the governor does nothing. Maybe they would rig a bell so that the balls rang it if the speed was too high !
Do you have Anthony Mounts build articles on this model, quite often he will say why he has deviated from the original, it's usually to do with items not scaling down well or for production reasons
Simplyloco, the conrod is 5 5/8" between ctr of big & little ends, the smallest dia of the rod is 1/4" but it all came out of a bit of 1 1/8 ENIA. Still a bit to do as well as cleaning up the machining marks.
I am just nearing the end of building this beam engine and have all the copy's from Engineering in Miniature which relate to its making. From this I would advise you to follow the drawings and not try to make it out of solid.The machining of part 31,cylinder valve face, needs to have the exhaust outlet machined and that alone could be a problem on holding in the lathe.
Just to give you a some thing to think about,
(1) part No 37, make the exhaust outlet boss longer than the 3mm stated, 4 or even 5mm would be better.
(2) do not drill the stud holes until after soldering, you can use the steam-chest as a template.
(3) Part No.36,the cylinder, make sure that the dimension of 34mm for the inner rim is on the plus side rather than minus, or you may find that the stud hole's break through the side. Again, make the cylinder cover and use this as a template for the holes.
And lastly, for all the tapping and drilling use some lubrication, small drills and tap's soon snap in bronze.
If I can be of further help please send let me know.
Post by classicsteve on Sept 15, 2009 21:05:07 GMT
Hey, thanks for the tips Gerry.
I only have the drawings and raw materials, and being a relative novice I have a lot of thinking on my hands as to the order of doing things. But that is all part of the fun. The object is to improve my modelling ability.
I am very surprised that the beam doesn't have pivot bosses like the original - I can't understand why they didn't include them in the casting. I have changed the beam pivot arrangement so it is a one piece pivot with bosses screwed on from either side to look the part.
Also it looks like one of the valve chest studs will break into the exhaust port the way it is drawn.
But it is coming along slowly - as and when time permits. A few hours a week at most - as there is plenty of full sized machinery demanding my attention.
Like you I am on a steep learning curve and this is the first beam engine I have built. So far it has taken me a year and 5 months to make in my spare time but the satisfaction comes from building it and not from having a model on show. I am told that the alterations or rather the deviations from the original one is to make it easier to build. But as there are 99 page's, one for each part, I really do think that they should have given an assembly drawing, they could have used the first five pages for this.
Have you seen the original engine ? I have seen the photo taken from the stair well but would have liked to have seen the other side view because I would be interested to see if it doe's have the crank shaft support bearing sat on top of a plain cast block.
I have just a few photos of our Stothert and Pitt, if you need any specific details please send me a PM and I will try to send you a copy of anything I have.
My 1/6th engine is currently awaiting for the midlands show to purchase two 1/4" ball cutters to enable me to machine the fluting on the inside rim of the Beam.
In response to the question on the outside bearing block: it sits on a not very sexy slightly tapered concrete plinth with a token steeper taper on the top edge. One may question if they got the height wrong as it has two (rough) square spacers the width of the pedestal making up the short fall in height. The main concrete plinth also has the same slight taper and spacers so lets assume that the spacers are there to level up the engine.
Post by classicsteve on Sept 21, 2009 20:40:42 GMT
Interesting link - he says it is for a grasshopper, and most of the Easton & Amos engines have the valve chest at the top end of the cylinder. I still haven't figured out why.
But I don't have CNC, or anything like it. I was thinking of turning an off-centre bore and flanges as my register, then mounting upright on my rotary table in the Centec and using an end mill in the horizontal spindle (or a ball end mill) to get the main profile.
It is probably impossible, but I thought it might be fun to give it a go. However main lathe is bunged up with some other work for the moment, so I have time to think about it.
One of the reasons I have been wondering about this is that I have some chunky cast iron, and have wondered if I could turn it into steam engine cylinders.