Another Stuart Twin Launch build started.

[David Shealey]

My dad got a Stuart Twin Launch kit as a retirement gift when he retired in 1980. He put together a small shop over a couple years, and barely started the work on this, but he passed away in 1984. I got the kit about 4 years ago planning to finish it one day.

Well, I have now started on it. My dad had only completed the base plate and main bearing caps, so not much was done. His long time work on all types of old engines led him to add Babbitt main bearings to the build. Somehow, he got the babbit off center, so the bearings are not constant babbitt thickness. I was thinking of getting some Babbitt and re-machining the castings, but upon removing the caps and looking at it, the bearing surfaces are really good, so will use as is. The 5/16 shaft turns easily and smoothly! Will have to do a lot of clean up and finishing of the base casting.
This will not be a build log, but will post mods and unique methods of fabrication. His kit did not include the reversing gear, so I will be making all that from scratch.

 

[David Shealey]

I have started the reversing gear, first done is the Eccentrics. I looked at every build post I could find on the Stuart Launches to get other's build procedures. One thing I did like was one that made the eccentrics with outside flanges instead of the little centralized bosses. Makes it a lot easier to get the bearing surfaces the right diameter and smooth. I came up with a method of machining these I have not seen before. I made a fixture that locates them on the hub, with a dowel pin in the eccentric that locates in two holes to get the angle spacing. Made them from 303 Stainless Steel, and ground the bearing surfaces with a home made tool post grinder.

 

[Rudy from Norway]

David, you have already done a great job here! Like the way you make the eccentrics. I actually remade mine on my 10V to something similar. Makes a better bearing surface.

I will do a Twin Launch my selves (I have a thread on a "Modified Expansion Engine). I think this is a very good representation of a classic steam engine used in so many smaller boats those days. All moving parts are so visible and it is a pretty little thing. However, it has a challenge (this style of engine), at least to me. The cross head guides are hanging more or less in the free. The cylinders and crank case is separated by columns that gives little reference between the two halves. Compared to other engines with a solid "A" shape standard with guide for the cross head, that can be made in the lathe or mill with exceptional precision beyond the accuracy of your chuck or tools in general. Simply by doing clever setups.
So the Twin Launch intrigues me because I don't see any obvious way to make the cross head travle in line with the cylinder bore, other than go by the numbers in the drawing. This means I can't exploit the intrinsic accuracy I can achieve by machining a part from start to finish while left in the machine all the time. My approach is always a smooth running engine with no binding or slack, right from the start. No need for running in to make it turn freely, just like an engine from a car manufacturer. However, this is me and I fully accept the method of making it tight from the start and run it in to smooth everything out. In this case this might be the best approach.
I will follow you project with interest. Good luck!
Rudy

 

[David Shealey]

Thanks Rudy! I am quite particular about the way I do things too. 10 years as a tool and die maker and machine builder, followed by 40+ years as a machine design engineer. Professional CAD user since mid '80s. I am currently working on the eccentric con rods from bronze bar stock, spending more time on the tooling and fixturing than will likely be spent on the parts themselves. I will post about that as I get into machining them. I had an old Palmgren dual X/Y table I used on a drill press for small parts before getting a Bridgeport. I am currently adding iGaging absolute DROs to it. I had done some pretty complicated parts on in the past, but counting and reading the little dials on it was not fun. I have a rotary table for the Bridgeport and will mount the X/Y table to that, so will have a "Manual CnC" (Crank n Crank) setup. I know I could do a lot of the parts by hand with sawing and sanding/grinding, but decades of designing and building machines with all machined parts and little to no hand work, just cannot do this differently. 8>)

 

[Rudy from Norway]

David, I suspected you where a bit above an average hobby machinist .
I'm particularly interested in how to achieve accuracy, so I'm looking forward to see how you will solve the cross head task.
I have an idea my selves, but that includes some modifications to the design. I will still keep the original style though.
Haven't decided if I will buy the kit or just the plans and maybe the cylinder casting. Not to save the $, but I like to make things my selves. Making parts from castings is actually more difficult than making from scratch i think, but making from scratch, looking like castings is pretty difficult.
Rudy

 

[David Shealey]

The plans are pretty dismal, basic is not even a good description. Glad I spent decades doing mechanical design work, I can only imagine the difficulty of making sense of the plans by a hobbiest that has not had a lot of experience. I am doing this project mostly as a sentimental thing, since my Dad wanted one for years, got it as a retirement gift, but passed away before he got to do much with it. I am doing all the reversing gear from scratch, as none of that was in his kit. The cylinder casting is about the only thing that would be difficult to do from raw stock and have it look like an old engine. Would be pretty easy though if one wanted a more modern look.

 

[David Shealey]

My lathe and mill.

 

[Rudy from Norway]

Nice shop David. You got some seriously good machinery for a hobby shop.
Agree about the DRO. I Can't even imagine doing anything without. Got it installed both on my mill and lathe.
Stuart has a good reputation, but I don't quite agree. Have just one kit under my belt, but i had to get two of the castings replaced due to poor quality. I found the plans ok, but I had to figure out the important stuff my selves. I invented my own therms and put abbreviations on the plans to help me keep track on what to pay attention to. Like: "R" meaning Related to another part and remember to fit it to this. And "CR", Critical Relation to another part, meaning something like sliding tight fit. And "CRA", Critical Related Assembly, meaning several parts has to be thoroughly fitted together and figure out the sequence to make them. "NC", Non critical, go by the measurements in the plans.
This helped me to do things in right sequence and plan ahead for the best possible setups.
The result was an engine running at 0,44 PSI with no clunking or tight spots, and no need for running in, so I'm pleased with that.

Here is a peak at my shop and my Stuart 10V.
Rudy

 

[David Shealey]

Nice shop! Wish I could keep mine that clean. I put 3 axis DRO on my mill as soon as I got it. Had the lathe for a few years before adding the DRO, what a difference! I "grew up" running machines years before DRO's were even a thing. Quite a few years "dial counting, then Trav-A-Dials came out, that was an improvement, then the first DRO's a year or two before I moved into engineering and design.
After decades of design work, first look at the Stuart drawings was shocking. I have done CAD models and drawings of the parts I am making from scratch. The Stuart drawings are basically "Make it kinda like this." 8>) I thought of 3d modeling the whole engine, but that would take quite a bit of time, not sure it would be worth the effort, but would make design upgrading easier.

 

[accelo]

Rudy;
I love your nomenclature;
Like: "R" meaning Related to another part and remember to fit it to this. And "CR", Critical Relation to another part, meaning something like sliding tight fit. And "CRA", Critical Related Assembly
The mistakes I made on my Snow engine are all in the "related to" category.
Like machining pillow blocks individually instead of mounting them and then completing the align boring.
Nothing in the plans about the procedure either.
I know everyone figures this out,on their first model. But I would certainly wish they had spend more time on the instructions!
The assumption is always the machinist is an experienced builder. Which isn't always true.
My other beef is the lack of overall dimensions. Typically the CAD program will chastise you for over-defining.
Gee, make it easy to at least pick up the correct blank without adding up 5 dimensions and two radius.
Rick

 

[Jules]

Rudy;
I love your nomenclature;
Like: "R" meaning Related to another part and remember to fit it to this. And "CR", Critical Relation to another part, meaning something like sliding tight fit. And "CRA", Critical Related Assembly
The mistakes I made on my Snow engine are all in the "related to" category.
Like machining pillow blocks individually instead of mounting them and then completing the align boring.
Nothing in the plans about the procedure either.
I know everyone figures this out,on their first model. But I would certainly wish they had spend more time on the instructions!
The assumption is always the machinist is an experienced builder. Which isn't always true.
My other beef is the lack of overall dimensions. Typically the CAD program will chastise you for over-defining.
Gee, make it easy to at least pick up the correct blank without adding up 5 dimensions and two radius.
Rick

I believe one the aims of the Stuart engines is to teach you about building assemblies. Checking drawings and working out the best methods of producing the model.
They have not changed a lot in decades.
If they were easy then you wouldn’t learn as much.
I made a few mistakes making mine but I doubt (hope) I don’t make the same mistakes again.

 

[David Shealey]

I was not sure how the valve timing worked, with the 40 deg difference in the eccentric, so I spent the last couple days modeling the reversing assembly and one piston in Solidworks. After running motion study, I see that it works very well. I posted a short video of the simulation on Youtube. The valve openings are sketch lines to see how the valve timing is with the piston movement both directions. Video is here:

 

[David Shealey]

Putting the engine together over the past couple weeks, got one cylinder timed fairly well, but see that it will never be the same between forward and reverse, will have to settle for best combination. Now started the other cylinder, but it was WAY off! I have read every posting I could find on these engines (Twin Launch), but have never seen anything stating that the eccentrics have to be opposite hand! The Stewart drawings show only one, but if assembled with the hubs facing outward on each end, one will have to be opposite, with the angle offset opposite from the other facing the hub end. 8>( Grrrrr. I was pretty upset thinking I would have to make one over from scratch, but think I can save it by boring it out and inserting a new hub with the extension on the opposite side.
EDIT: My mistake, all I had to do was reverse the valve actuation connecting rods on that side! Relieved!

 

[xpylonracer]

Smart video David, better than a thousand words.

 

[David Shealey]

Smart video David, better than a thousand words.

Thanks!

 

[David Shealey]

Here are pictures of my CAD design of the fixturing for most of the reversing gear parts. Sometimes fixture design and build takes longer than making the part!

 

[David Shealey]

I did the machining of the parts shown on the fixture using an XY stage with iGuaging digital readouts, mounted on a rotary table, on my Bridgeport with digital readout. My own manual CnC (Crank n Crank). I did drawings of the parts in Solidworks, with all the angles and locations to follow.

 

[David Shealey]

I did the Crankshaft much as I did the eccentrics, mounted in a fixture that located on the crank centerline with the correct offset for the crankpins, and the crank web located in a slot in the fixture. That made machining the crank easy, and precision. Much better than most of the ways I have seen these done.

 

[David Shealey]

I originally made the valve eccentrics with set screws, but hated the idea from the start. My many decades as a machinist/tool and die maker/machine design engineer made me hate set screws on shafts with a blinding purple passion! I decided that was not going to happen, so modified them by turning the hub down, slitting it, and making a clamp to clamp it on the shaft. That makes timing much better, and will not mar the shaft in any way!

 

[David Shealey]

I modified the design of the reversing lever stops to make the stops adjustable, also mounted to one of the steam shaft studs on a little bronze bushing so that timing can be done with the steam chest cover plate removed.