Stuart Beam Engine in Diorama

[J.L.]

I made it clear early on, that for some elements of my models, I do not have the equipment  or experience to make them accurately. Such is the case with several items upcoming. I did not make the con rod or the eight levers that will control the movement of the piston rod.

I guess the balance is to know when to step aside and get help to keep the project enjoyable and avoid stress or frustration.

Mind you that may still come when I attempt to run this puppy! 

So, here is the connecting rod with the little parts I was able to add.

[J.L.]

Fred, drilling and reaming that 7/16" central bearing hole made it so easy to machine the cast iron beam on the miling machine.

In the first photo of the unfinished beam installed, the crank is at six o'clock. The second; twelve o'clock.

Now, how does an arching beam lift vertically? 

That's what I intend to discover this week.

 

[b.lindsey]

Ah yes, the beam makes it look more complete, even though there are more bits to add i know. Looks great John.

Bill

[J.L.]

All eight levers that magically (?) control the movement of the piston rod measure 1 3/4" on centers. When I placed the first one between the beam's end hole to the hole in the top of the cylinder shaft, the lever was too long. That meant that the piston rod was too long.

In going back to the diagrams, I noticed that there is no dimenstion given for the length of the piston rod. Now I see why. You are on your own to determine its length specific to  your machine. 

I will have to make a new pistron rod that will allow the lever to connect properly.

I would think this could be tricky. You don't want the piston to slam down into the the cylinder's base or slam up against the piston's cap.

X-ray vision could  be useful here. 

[mklotz]

Is this model to have the famous Watt's parallel motion linkage? 

If it is, there are numerous descriptions and animations on the web, some of which even discuss the geometry,  e.g...

https://en.wikipedia.org/wiki/Parallel_motion

Perhaps this (or similar if it's not Watt's linkage) would be helpful in working out the geometry for the model.

[J.L.]

Hi Marv,

Thank you very much for giving me a link where I can wrap my head around how these parallel motion levers operate.

Yes, the Watt's system is what will be employed.

Kind of you.

John

[Jasonb]

John, there is a length given for the piston rod - top of piston to ctr of hole in the rod end = 3 9/16" Book does say that this distance can be adjusted by screwing the rod end up or down to get the piston central in the cylinder

Not sure what you mean by "the hole in the top of the cylinder shaft"

[J.L.]

Hi Jason,

A senior moment there. You are right. The diagram does show a dimension of 3 9/16" from the top of the cylinder face to the center of the cross hole in the piston rod cap. The printed dimension was far out from the part for these old eyes. I must have seen it earlier, because I made the part! 

Originally, I threaded the top of the piston rod sufficiently, but did not thread the mating threaded hole in the piston rod cap deep enough to let it thread down to the 3  9/16".

I also checked to make sure the con rod was 6 1/4" center to center.

You know Jason, the upcoming Watt's pivoting lever system could drive one to drink! 

So another try today to get this teeter-totter working.

[J.L.]

Hi Bill,

Sorry I didn't acknowledge your earlier complimentary comment.

Thanks. The beam does make a statement. I am waiting for the day when I see in rising and falling slowly through the beam floor upstairs when we get the diroama made.

Cheers...John

[J.L.]

In most of the drawings I've seen showing cast beams, I've noticed that almost invariably there is a cast rib through its center joining the bosses. I would think it common practice in the pattern making shop to include one for strength and perhaps even appearance.

Here's a photo of one that may be a bit over the top with the number of ribs,  but the principle of strength and stability is definitely there.

I'm using Bondo auto finishing putty here to create fillets to make the 1/16" square brass strips look cast - otherwise, they would look as though they had just been stuck on. 

[b.lindsey]

The drawing is more "Victorian" perhaps when beauty as well as function was important, but yours looks every bit the part too John and once cleaned up and painted will certainly look cast in as well.

Bill

[J.L.]

Yes Bill,

The paint went on today. Now I have to keep my hands off of it for 48 hours. Initially, it dries in minutes, but takes days to harden properly. I'm often been guilty of handling painted parts when they feel dry, but soon regret it.

So, in the meantime, the table saw has been cutting some walls!!! Each wall has to be designed to be totally 'break down', so access to the engine can be achieved instantly.

[J.L.]

While the paint dries ,(and before I step into attempting to attach the linkage for the piston rod), I cut the west and south walls for the diorama. Tom, you can clearly see your Corian base here.

The fasteners are designed for MDF so that threaded bolts can be used as in some knock-down furniture. The large fixtures are threaded in with a hex wrench.

[b.lindsey]

John, do you also glue those fixtures into the MDF or do they hold well enough on their own? Just curious.

Bill

[J.L.]

Hi Bill,

A good question. The sharp splines on the threads are very aggressive and will hold fast and stop your hex wrench! You have to drill a large hole (3/8") to have them engage without putting stress on the material around the hole.

There are two types of fixtures. The flanged ones on the left are metric threaded; the plain ones on the right in the first photo are 1/4 -20 threaded.

There is also another type of fastener (second photo) I will be using on the walls of the diorama. The walls are only 1/2" thick, so a metal cross dowel is used. The slot lets you rotate the dowel to engage the bolt coming to meet it that has been drilled in the end of the thin wall.