Stuart Triple Scale Up

[Milan Machine Worrks]

Hi

Here's a PDF drawing of a Stuart Triple Expansion Steam Engine bed plate drawing that's scaled up 100% I'm planing on machining this from a billet of 6061 t6 ( I should have got 7075 but live and learn) Been working on the tool paths and stock setup. I'm slowly redrawing the engine 2:1


Roland

View attachment Bed Plate - Rev B.pdf

View attachment Bed Plate - Rev B.pdf

 

[Milan Machine Worrks]

Hi

Here's a couple rendering's of my Stuart Triple project so far, I can't decide on the type of fasteners to use cap screws or hex nuts any suggestions?

Roland

View attachment Image HSM.bmp

 

[Milan Machine Worrks]

2nd one

View attachment Image HSM 2.bmp

 

[tel]

That's going to be one serious hunk of engine. You'll certainly have my attention during the build. BUT .......... socket cap screws have no place on an engine of such grace and beauty - hex's please, and preferably nuts on studs!

 

[ozzie46]

I agree whole heartedly with Tel. Studs and nuts.

Ron

 

[GWRdriver]

Roland,
I assume you are doubling (2X) the Stuart engine and to me that would be 200%. (Original engine = 100%? Then 2x 100% = 200%) But either way, a model of this size will present you with the opportunity to make a lot of things more faithful to prototypical practice, if that's something that's of interest to you.

I agree with the comments on studs & nuts, but something else that jumps out at me are the bearing caps. An engine of this size and complexity would not have had simple flat strap bearing caps. The drawing below is the bearing pedestal of a stationary engine but marine practice would have been very similar, especially in larger engines like triples. It also illustrates one place where and how nut & studs are used.

In general, the cylinder heads had a large number of small diameter studs (and nuts) rather than a fewer number of larger ones, so as at least a nod to prototypical practice when setting out the cylinder cover studs it would be appropriate to go one or two screw sizes smaller and put more in. Also it would have been appropriate for this engine to have cylinder relief valves in the heads and if I can find a picture I'll post it. These wouldn't need to be working valves but convincing replicas would be easy to make. This should be an interesting project.

Harry

 

[Milan Machine Worrks]

Hi Harry

I agree about the the bearing caps and I'll redesign them to look more like the ones in the drawing you posted,I don't don't know much about the engines and was going completely by the Stuart drawings. I'd like to change the bolt circle for the top and bottom covers. Any suggestion about how many more fasteners I should add? I'm using 6-32 to 12-24 fasteners I thought the 1/4-20s were way to big. Yes I've been doubling the dimension and actually its 4 times as big. The crankshaft is 18.25 long. I only have one part machined so far the bed plate. Here's a photo, Right out of the machine, still needs some hand finishing. And it will be studs and nuts. Thanks for suggestion and ideas.


Roland

 

[GWRdriver]

Consideraing this is a general representation model rather than a fine scale replica, and without adding too much additional work which would be over-kill compared to the level of detail on the rest of the engine, looking at the head bolt patterns on your prints I'd be inclined to double the number of studs shown and reduce the stud size accordingly. Since I don't know what the head diameter is I can't say exactly what screw size I might use, maybe #4s or #5s.

Harry

 

[Maryak]

I agree with the comments on studs & nuts, but something else that jumps out at me are the bearing caps. An engine of this size and complexity would not have had simple flat strap bearing caps.
Harry

Sorry but most 20th century English triple expansion engines had exactly that, simple flat strap bearing caps. We had 3 such engines at my last place of employment, 2 with round columns and one with rectangular columns, all had simple flat strap bearing caps on the mains. It's far easier to mount the worsted box on a flat strap bearing cap.

Best Regards
Bob

 

[steamer]

Often times the "Worsted Box" on the bearing caps had a door you flipped up and poured the oil in....then closed......then again, there's probably as many box designs as there are bearing cap designs...do what ever floats the boat... ;D

Nice rendering....if your going to use steam, I would recommend Iron for the block.....

Dave

 

[kvom]

Been working on the tool paths and stock setup

Does this mean you are doing the g-code programming as opposed to using a CAM system?

In any case, a 2x scale up means an 8x increase in material and weight, as well as 8x displacement. That will be a hefty engine.

 

[Milan Machine Worrks]

Hi Kvom

No, I use a cam program, Mastercam X2 and Autodesk Inventor ( inventor can be had for cheap on E-bay) for the 3d modeling,the bed plate alone had somewhere around 500,000 line of code to cut the top and bottom. It would be a daunting task to write G code for contour cuts like that. Yes your right 8x the material the bed plate is four times the size of the original drawing. (2xL 2xW 2xH) I really wanted to enlarge the drawings 2.5 but the cost of materials was just to expensive the stock for the bed plate was $102.00 with the shipping. Oh I just want to bring to light that Speedy Metal's prices should be check against Metal Express, the stock for the main bearing is more than 30.00 more from speedy metals vs Metal Express.

Roland

 

[GWRdriver]

. . . then again, there's probably as many box designs as there are bearing cap designs...do what ever floats the boat - Dave

Precisely. Here's a photo of a popular model triple (the O.B. Bolton engine) which shows the cylinder relief valves. These took several shapes, and certainly weren't present on every single vertical marine engine ever built, but are not out of place on any large triple. Unfortunately the slotted-head screws in the cylinder cleading (lagging) takes away from the otherwise nice appearance of this engine.

 

[Milan Machine Worrks]

Hi

Another rendering with studs,hex nuts and a few more details.

Roland

View attachment 22.bmp

 

[Jasonb]

There are a few pictures of marine engines here which should give an idea of the types of bearing caps and oiling methods you could go for. My TE has small oil boxed as previously mentioned, should be about the same size as your engine so quite doable.

I would also change the supply & exhaust plumbing to flanged joints not screwed in like the stuart. Maybe also add a condenser and plumbed in oiling and drain cocks.

Jason

 

[steamer]

Definitly go with the flange pipe fittings....keep the oil lines really thin to keep with scale appearance.