Stuart Triple Expansion

[jwloach]

I remember well my grandfather building the Stuart Triple in 1966 when I was about 11 years old. Very exciting. Now it needs some loving care - lots of grime. I disassembled it, ordered the drawings from Stuart, and have 3D modelled the engine with IronCad. The digital assembly is done, now begins the constraining of parts and animating. The 3D modelling will help with the reassembly immensely. Here are some photos. I'll update this as things progress.

Thank you! John (Toronto, Canada)

[kvom]

Should be great when you're finished.

[Chipswitheverything]

Your digital work on the Triple is an interesting approach to getting to know its componentry.  My take on the refurbishment work would be - as with my own engines during the construction over long periods - to arrange a system of being absolutely sure of the relationship of individual parts to those that they must fit back to, so all eccentric sheaves, for instance, will return only to the specific eccentric, and the right ( original ) way round ... 
Could be that your grandfather marked the various components in some way, pop marks, scratches? . I have tended to use multi compartment trays to lay out and separate the many items, including the screws and fasteners, along with small label notes to help identify points to note.  In model engineering work, it's a bit rare to find the interchangeability that commercial production engineering would take for granted!  Dave

[jwloach]

Thank you! The 3D model is finished now, and  all of the holes, faces, slots line up. What a relief. I'm quite sure the reassembly will go OK, but I'm a bit worried about the several shims that my grandfather had placed between pieces to allow them to move more freely. I've lost track of where they were. Also, the fasteners may require a bit of thought.

I'm amazed at the accuracy of the 3D model though. I have all the constraints working so that the reversing arc guides move correctly through the engine cycle. I'm working now on the constraints required to turn the wheel from forward to reverse. Very smart people 'way back when.

Also, I have to set the eccentric sheaves on the crank shaft to expose the ports correctly as the shaft turns. It's amazing how realistic 3D modelling is. You feel like you're actually working with physical components.

Cheers, John

[jwloach]

Hi all. Here are three animations - the triple running forward, running in reverse, and transitioning from forward to reverse.

Now I can begin reassembling the model!

Cheers, John

[crueby]

Great work!  Are you going to use the CAD model to build a new engine, could scale it up or down as needed too?

[jwloach]

Thank you! Somebody said that we should 3D print the model now that all the part drawings have been digitized. Hmmm - got enough to do ... must reassemble that pile of real parts first!

[jwloach]

Mac users can't play avi files, so here are mp4s.

[steam guy willy]

hi do you also have type in all the tolerances between the moving parts ?? as we all know a 1" piston will not enter a 1" bore ??!!!
 willy

[jwloach]

My grandfather ran the engine with compressed air, but he had to remove all the piston rings to make it cycle easily enough. Perhaps he didn't let it 'run-in' long enough. I'll start the reassembly after freshening up the paint on the base and cyclinder housings.

[jwloach]

I haven't made 2D machining drawings of the parts - just their 3D renderings. The drawings from Stuart are very minimal - no tolerances shown. They leave a lot to the modeller's imagination!

[AVTUR]

John

Believe me, Stuart drawings are good by model engineering standards. I have drawings for the 7A and two cylinder marine compound engines. There are no mistakes and the projection is clearly stated. However the drawings are very cluttered. There are no tolerances since these are not understood, or misunderstood, by many model makers. There are better draughtsmen, such as Anthony Mount, and there are far worse. Edgar Westbury's drawings usually have mistakes and many of the loco designers did not understand projections.

When I returned to model making after retirement I did not understand the lack of tolerances. I still mentally work to a tolerance and wonder why my results are tight.

Anyway, welcome to the forum and have fun.

AVTUR

[steamer]

My grandfather ran the engine with compressed air, but he had to remove all the piston rings to make it cycle easily enough. Perhaps he didn't let it 'run-in' long enough. I'll start the reassembly after freshening up the paint on the base and cyclinder housings.

The problem with running a triple on compressed air, is air does not behave the same as steam.   The available expansion of compressed air in the 120 psi range is quite limited compared to that of steam.  The result is the IP and LP cylinders will over expand the be operating under a vacuum, in opposition to the HP ( high pressure) cylinder.    This results in lumpy running   if you open the drain cocks on the IP and LP it will help a lot,   Additionally, you could run some compressed air to the IP and LP.

Dave

[AVTUR]

My grandfather ran the engine with compressed air, but he had to remove all the piston rings to make it cycle easily enough. Perhaps he didn't let it 'run-in' long enough. I'll start the reassembly after freshening up the paint on the base and cyclinder housings.

The problem with running a triple on compressed air, is air does not behave the same as steam.   The available expansion of compressed air in the 120 psi range is quite limited compared to that of steam.  The result is the IP and LP cylinders will over expand the be operating under a vacuum, in opposition to the HP ( high pressure) cylinder.    This results in lumpy running   if you open the drain cocks on the IP and LP it will help a lot,   Additionally, you could run some compressed air to the IP and LP.

Dave

Does the engine have a simpling valve? This is a valve that allows high pressure steam to be fed into the valve chest of a lower pressure cylinder. It is used to start the engine when the high pressure piston is close to top or bottom dead centre. Without it the engine may not start. One can be made and fitted with ease.

AVTUR

[jwloach]

Wow! I've got a lot to learn! My grandfather made two other Stuart models, and my Dad made a Rider-Ericcson engine from Myers Engineworks in 1998. None have run on steam, but that would be a worthwhile project. Thank you all for your encouragement and thoughts.