Stuart Compound Twin Build -

[jpdenver]

Hello all,
I am a relative newbe here and in a machine shop.
A little background -
I am an almost-retired electrical engineer, still have a day job
as a contractor for certain government agencies.
I am self-taught as a machinist, and have slowly built up a
small shop. I use a Sherline Lathe and Mill, with a collection of
accompanying grinders, belt sanders (linishers) and stuff.

I started on this hobby path about 6 years ago, and have built a
lot of small stuff, finishing up last year with a Stuart D10.

I put my engines in boats. And have joined a model boat club
in order to have a place to play with them.

I bought a Casting Set from Stuart about 6 years ago, and at that time
I was intimidated by the prospect of working on the cylinder block,
(I had not started making chips yet) - so I arranged to have someone with
a surface grinder do some preparation for me. This gave me a good starting surface.
I put the set on the shelf until last month, when I decided to make it my next (second)
build.

I found a site, modelengines.info (yes-that is the correct URL) and struck up a conversation with John Bentley. He has been an incredible resource, and I plan on engaging with him as I go along if I get stuck.

I am also looking forward to the community I see here.

SO -Here we go.

A page from the Stuart Catalog.

A finished engine, Hope mine looks as good.

The casting set - The cylinder block has been squared up, but not finished to size yet.

The extra pieces "not included" in the kit - Rods and bars.

This is my "Build Log" - I have taken the drawing set and after making a copy
in order to lighten up the paper, I have cut the copy into individual parts
so each part has a separate page in the log. The idea is to have a way of keeping
the calculations I need for each part and to have something to refer to as the
build progresses.

In the coming days, I will try and capture the process I follow as I go
through the build. Since I am a rank beginner, I will ask for your help and guidence
when I hit a snag, or a difficult process or setup.

So - Thank you for reading,
Please enjoy the journey.


Regards to all,
Jim Pope
Denver, CO
USA

 

[JimDobson]

Looking forward to following along the build with you.

 

[jpdenver]

Thanks Jim

 

[jpdenver]

CYLINDER BLOCK

I started to work on the block today.
After studying the Plans for the block,
I came to the conclusion that Stuart leaves a lot of valuable information
hidden on their plans. You have to use a bit of circular logic to extract
something that is relatively inportant - like HOW TO LOCATE THE CENTER OF THE CYLINDERS.

I reached out to John Bentley and he was kind enough to provide me with the missing dimension, I still do not see where he got it!

By using a piece of plastic card - I was able to locate the corner points of the posts. Everything is built by referencing to the BOTTOM
of the cylinder block, so the initial locations become important points for all sorts of future calculations.

With the points laid out, I was able to do my first setup.
I used two 1/4 inch tool blanks as stand-offs.
Started to bore the L.P. (Large) Cylinder.

At the conlclusion of the bore process, I found that one of my steam ports on the L.P. Cylinder had a "chip".

The port is no longer a rectangle -

Sorry about the focus - but you can see the chip -

So I ask the forum - IS THIS A PROBLEM?

Thanks for reading,

Jim Pope
Denver, CO
USA

 

[Charles Lamont]

Castings cannot be relied upon for precise dimensions. You are supposed to examine them and decide for yourself where best to put the datums. You want to try to ensure that features that will not be machined end up well positioned, while also making sure that there is sufficient metal for machined surfaces to clean up. You want the column holes central in the feet. You want the cylinder wall thickness equal all round. You want the ports central in the port faces. You want the cover flanges equal thickness top and bottom. All these requirements will probably conflict a little. You have to determine the best compromise.You have to decide where you may need to do a bit of cosmetic filing.

The shape of the cylinder port is not important. It does not affect timing or anything. If it were very much too large then you could get problems with trapping piston rings.

 

[deeferdog]

Hi Jim, following this with interest. Expect to make mistakes, we all do. Casting kits are often a real challenge, I would rather a scratch build as I personally find them easier. There are a great bunch of people on this site who have helped me immensely over the years and I'm sure will do the same for you, never be afraid to ask. Cheers, Peter

 

[jpdenver]

Thanks for all the replies-
"Full Steam Ahead"!! (pun intended)

Moving on to the port faces.
I measured the Distance from the edge of the LP Cylinder to the LP Portface, and then
used an endmill to bring that into correct dimension.

Then I flipped the Cylinder over and milled it to the final length.

After that end was complete, I polished both ends using 400 W/D paper.

Looking at the Ports and Plans, I find that I am very lucky -
both sets of ports require only a little "squaring the corners"
and everything else is right on target.

Finally - everything was sent to the "Shop Steward" for inspection.
(Required treats as payment in order to pass)

On to the next step. -

I am going to work on Cylinder covers next, this will establish the bolt pattern
and stud location for the cylinders.

Thanks for reading,

Jim Pope
Denver, CO
USA

 

[jpdenver]

The Cylinder Covers

The Hi and Low pressure covers came as castings and were reasonably symmetrical.

There was a raised area on the underside meant to fit into the cylinder. I used this as
my "indication point" and worked all the rest of the measurements off that.

SO I chucked up the Low Pressure (Larger) cover and used a center drill to give me a stable point to apply some additonal
pressure and keep things steady.

With the exception of a little "lip" near the jaws, I brought the cover to as close as I felt comfortable with
as far as a total circumference was concerned.

Then I flipped it over and worked on the inside.

I faced the underside and brought things into proper size, I used a boring bar to work on the underside "indentation" .

Then I checked the fit with the cylinder block.

I approached the Hi Pressure Top the same way.

First bring it into a close size, flip it over and work on the underside,
then flip it back and finish up the dome.

And a final check on the cylinder block.

Looks like the top of the block is a little "FAT" on one side. The boring of the cylinders was all performed measuring from the
underside of the block. I have not done any trimming of the block at this point - meaning the width of the steam chests, so
I will have to study this a bit more.

I know that there is a mixed set of viewpoints as to which form the cylinder covers should take, either Domed or Flattened.
I have chosen domed.

What I am not sure of is the relationship of the piston to the underside of the covers.
The drawings indicate a general shape similarity - So I will have to pay attention here too.

Last but not least, a good polish with emory paper followed by 400 g w/d to make em look pretty.

Next I will work on the cylinder bottoms. Again I plan on getting the shaping out of the way prior to drilling any
holes in the cylinder block.

Thanks for reading,
All comments and suggestions welcome.

Regards,
Jim Pope
Denver, CO
USA

 

[Jayarebee]

Hi Jim, the top covers look great. They will be even more fun once the flats are on them so both will fit in place at the same time. The question of flat or domed tops is probably personal choice and the domed type seems to be more common in models, including the compound pictured on Stuart's website. Some engines even have very shallow cone shaped top covers. In full size practice the larger ship engines tended to have flat tops and often with round fracture grooves to allow the covers to burst instead of the cylinder block if overpressurized.

 

[jpdenver]

The Cylinder Bottoms

After taking some time off to visit with Grand-kids, I started to work on the cylinder bottoms.

Started with the High Pressure, I gripped it from behind and then faced it and drilled a center
spot. Using what I call a "pressue-point" which is a home-brewed device I saw in a book somewhere,
I kept pressure on the casting while I worked the face a little more.

Then I drilled the center hole, starting small - larger, and then finishing with a reamer.

Then I bored out the portion for the gland packing ----

Now the "inside side" Put it in a 4 jaw, and used a rod held in my chuck to make sure I kept it all aligned....

Faced and shaped it to fit the drawings and checked the fit with the Cylinder Block.

My new Shop Supervisor, She tells me when I have too much swarf, and then helps with the vacuum.

More to come - next post continues ...

 

[jpdenver]

The Cylinder Bottoms -Part 2



Putting the High Pressure aside, I got to work on the low pressure.

I took a risk - and it seems to have paid off. I think that it shows the quality of this set of castings.
I very carefully loosened the 4 jaws just a quarter turn each, then removed the High Pressure Bottom, and replaced it with the Low Pressure Bottom. Tightened the jaws and put it back on the lathe spindle. Then I worked the face and drilled the hole for the
piston rod - this time from underneath. Once again checking the fit on the cylinder before I removed it from the 4-Jaw and
checked to see how "lucky" was.

After breathing a sigh of relief,

I use a synchronous 4-jaw to hold the Bottom from the "Inside Side" and worked the outside to dimension.

Finally boring out the hole for the packing gland..

And we are done.

Checking them against the Cylinder block under-side...

I think it is time to measure and drill some stud holes next.

Thanks for reading.

Jim Pope
Denver, CO

 

[deeferdog]

Looking good Jim. Like your work. Cheers, Peter.

 

[Jayarebee]

It's already starting to look like an engine in those bottom views of the block. I guess it pays to have a good shop supervisor! Keep up the great work Jim.
- John

 

[jpdenver]

BOLT HOLES

I started on the cylinder tops and bottoms bolt holes.

Mounted a rotary table, located it's center, and then mounted a 3-jaw chuck.

zeroed everything and set up origins for all the following operations:

Large and Small Cylinder bottoms,

Large and Small Cylinder Tops.

7 holes on the large cylinder
5 holes on the small

Overlap on one hole on both top and bottom.

Upon further inspection I found that the Cylinder Bottoms are just a little
out of perfect alignment. After reviewing the plans, I have come to the conclusion
that there is one critical alignment out of all the possible features.

The flats where the slides are attached need to be parallel to the plane formed by the
rear posts. The rest of the features of the bottoms, the glands and the holes are all
non-critical. But if the slaides are not parallel, things are sure to bind up.

See the pic - the pencil points to the flat in question.

I have decided to work on all the pieces that attach to the cylinder block BEFORE I start drilling holes in the block for studs.
This will make sure that all the possible relationships are taken into account while drilling.

So the next parts are the valve chests and covers.

So Thanks for reading -
More to come.

Regards,
Jim Pope
Denver, CO
USA

 

[David Shealey]

I will be following this! I have a twin launch kit inherited from my dad years ago, he had barely started anything on it. I am now retired, hope to start on it this year. He got the kit in the 1960's. It does not have the reversing addition, as it was an option then. I ordered a new set of plans from Stewart so I would have the needed information on those parts.

 

[Gerald Pierce]

Hello Jim,

It appears that you are using a Sherline lathe. You are making very good progress to date.

I built the Stuart Compound Launch about 15 years ago. I later added the reversing gear. I have a Maximat 7 lathe and an EMCO FB-2 milling and drilling machine. Since these are larger I could use other operations than you. I posted a picture of boring the cylinders and one showing all parts.

There is several possibilities of misalignment without the use jigs. The columns must be aligned with the bed centerline. Also, main bearings and cylinder bores must be aligned. This is difficult by just marking out. The use of jigs for this engine is described by Tubal Cain, ( Tom Walshaw, not the YouTube Tubal Cain), the author of several books on model engineering. The jigs are covered in his book "Simple Workshop Devices". One of the jigs is shown in the boring photos shown below.

I have also posted a video of the finished engine running on compressed air.

Since this is my first post, I hope everyone shows up in the post.

Gerald Pierce





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[jpdenver]

Gerald and David thanks for your comments.

I located my copy of Simple Workshop Devices - when I started learning about all of this I actually bought the set
of Workshop Practice Series books.

So picking up where I left off.

I went back to the bottom covers and finished the tapping for attaching the slides.

Before I start on the steam chests, I decided to clean up the SOLE PLATE. I wanted to get things ready for working on the
bearings, but I will get to those later.

For now I wanted to get it the right size and clean up the skin. I also marked out the positions for the future bearings
and also for the pillars that hold the cylinder block.

I am going to wait until I actually drill for the column tops on the cylinder block and then use that as the template for the
column bottom ends on the sole plate.

So that will be the next item.

Then on to the Steam chests.

Thanks for reading -

Jim Pope
Denver, CO

 

[jpdenver]

Ok, Not quite time for the Steam Chests.

Instead I decided to work on the posts and the holes for them
in both the Cylinder Block and the Sol Plate.

SO ---

First I worked on the tabs on the cylinder to thin them '
down to match the plans.

Then I got carried away and worked on the Block with a dremel
to clean up the various surfaces.

My plan is to first drill the tabs on the block, them use them to align for the Sol Plate.

While watching TV I decided I needed to sort thru the "Fixins" .

When I first got this kit, about 5 years ago, I received a small plastic
box with all the studs and such. About 2 years ago I built the Stuart D10
and some of the fixins were missing, so I stole from this kit in order to
finish. When I chose this kit for the next project, I ordered a replacement
Set of Fixins from Stuart. So if there looks to be more parts than normal -
you are right, It is nice to have some spares.

Now to the posts -

First the 4BA end -

Chucked up a 1/4 inch diameter Mild Steel rod and then
worked the end down to the thread size.

Then I mounted the die in a holder and used the tail-stock
to feed it on to the end. Put the nut on it to check out the
results.

Then the 2BA end.

I had some 2BA nuts, so I used one to test the thread as this end will be attached to the Sol Plate.

And then finished them all up with a shine and a polish.

Next I will actually drill and tap the holes. I will admit that a couple of the 2BA threads look a little meager.
Looks like a job for some Thread Locker just to make sure.


Thanks for reading,

Jim

 

[Jayarebee]

Jim, you are moving ahead by leaps and bounds and it's looking good! Nice to see the columns already. I'm sure it will be a good feeling to see the cylinder block sitting in its proper position above the sole plate. "Meager" BA threads usually tend hold surprisingly well compared to Unified threads due to their narrower angle. In any case you might want to hold off on the thread locker for quite a while - I bet you will be taking that thing apart and putting it back together more than a few times during construction!

Good progress,
John

 

[jpdenver]

HOLES FOR THE COLUMNS

Earlier - prior to boring the cylinder block, I marked out the position of the
holes for the top of the columns. So the plan is to drill these as marked, and then use
them as a "jig" for the sol plate lower end.

With that completed, I tested out the columns, and found that two were a little "wonky".

So I had a little file work to make the nuts sit flat.
I also have some "toothed" lock washers, and decided to add those
under the upper nuts.

Once I got that fixed, I used the block as a jig for the sol plate.

But first I studied the relationships and positions of future bearings and the crankshaft.

The Low Pressure cylinder is 1 1/4 inches in diameter - this means it will need to sit centered over the bearings
and will overlap 1/4 inch on each side. You will see what I mean in a moment.

The High Pressure cylinder is 3/4 in in diameter, and will also sit centered over the bearing opening -

So - If everything lines up, we will see the bearing markings in the LP hole and just barely see a sliver of
the sol plate thru the HP hole.

What you may not also see is that I have a small mark on the cylinder wall at the far end as a center guide. Lines up perfectly.

And just a reflection in the HP hole, as predicted. I love it when a plan comes together!

Used the "Clearance" drill of the cylinder as a spotter for the sol plate. I do not have a long center drill.

And then the rest.

And we have the Sol Plate - with the holes started, ready to go on and get sized for tapping.

(to be continued . . .)