# Stuart 5a stationay build

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I have done PLAN calculations before, and have those stored safely .......................somewhere.

My brain is doing like a hard drive that is running out of space, and so the new stuff is writing over the old stuff.

I recall comparing the PLAN equation with published hp for commercial smaller sized engines, and so that may be accurate enough for a comparision.

I have seen some wild ratings on newer steam engines (modern commerical units that are for sale), and they really don't seem to compare well with the old data when you compare the same bore, stroke, rpm, pressure, etc.

Here is a chart for O-S steam engines, and a 7" bore, 10" stroke at 150 rpm, assuming about 100 psi, is listed as 10 hp.

I found my PLAN spreadsheet, and it is as follows:

P = mean effective pressure (psi)
L = length of stroke
A = area of piston
N = revolutions per minute (rpm)

When I punch in the numbers for the 10hp 7" bore engine from the previous chart, I have to crank down the mean effective pressure to 40 psi to get to 10 hp (indicated).

The equation in my spreadsheet is:

(2*P*L*A*N) / 33,000

Where P is in psi, L is in feet, A is in sq.in., N is rpm.

I assume the 2 is because there are two power strokes per revolution for a double-acting steam engine.

The 33,000 is some constant number.

So cranking down a 2.25" bore engine with a 2" stroke, to P=40, I get about 0.5 hp at 300 rpm.

I am not really sure how to approximate the mean effective pressure.

And I am not positive my spreadsheet formula is correct.

.

Edit:

Looks like I posted this off-topic stuff right in the middle of Bob's 5A build thread.
Sorry about that; I was not paying attention to where I was posting.

.

I found my PLAN spreadsheet, and it is as follows:

P = mean effective pressure (psi)
L = length of stroke
A = area of piston
N = revolutions per minute (rpm)

When I punch in the numbers for the 10hp 7" bore engine from the previous chart, I have to crank down the mean effective pressure to 40 psi to get to 10 hp (indicated).

The equation in my spreadsheet is:

(2*P*L*A*N) / 33,000

Where P is in psi, L is in feet, A is in sq.in., N is rpm.

I assume the 2 is because there are two power strokes per revolution for a double-acting steam engine.

The 33,000 is some constant number.

So cranking down a 2.25" bore engine with a 2" stroke, to P=40, I get about 0.5 hp at 300 rpm.

I am not really sure how to approximate the mean effective pressure.

And I am not positive my spreadsheet formula is correct.

.

Edit:

Looks like I posted this off-topic stuff right in the middle of Bob's 5A build thread.
Sorry about that; I was not paying attention to where I was posting.

.
I forgot about that 2 multiplier, thanx. However, My calculation came ouit at 5.78 hp. Must have gotten a decimal out of order.

Lets do a quick calc for the 5A.

P = 40 psi (an assumed number that may or may not be accurate)

L = 2/12 = 0.166666

A = pi * 2.25/2 squared

N = 300 rpm (assumed value)

Horsepower (indicated) = (2*P*L*A*N) / 33,000

{ 2 * 40 * 0.166666 * 3.97 * 300 } / 33,000 = 0.48 hp (indicated)

.

At 800 rpm, the equation above yields 1.28 hp (indicated).

Seems like they are using the rpm to inflate the hp a bit.

.

Thanks packrat, this build is going well.

Time to get started on the engine standard. The rough casting is absolutely fabulous. It machines very well and has a smooth nice finish. It is very symmetrical all around which makes setup easy. A couple of small holes here and there, nothing to worry about. The first step is machining the bottom of the feet. Plug the bottom of the cored hole with an aluminum rod. This end of the cored hole was very smooth, and the plug gently tapped in.

View attachment 150220

Next, plug the top of the core and center the standard as truly as possible on the faceplate. This end of the core was rather rough, so I used two-part epoxy to install the plug. Center drill the plug and support with the tailstock. Turn the top face of the standard and the rim to final dimensions. Face the top as close to the plug as possible without digging into it.

View attachment 150221

Boring out the crosshead guide part of the standard requires the use of a steady rest. The standard sticks out too far to turn without the extra support. The steady rest that came with this lathe does not have the capacity for the standard. I fabricated this one from some 6” steel pipe and bar stock. The rubbing surfaces are hard bronze. Install the steady rest without disturbing the faceplate setup.

View attachment 150222

Drill and bore out the plug.

View attachment 150223

Rough out the crosshead guide bore. Get to within about 0.010” for the final inside diameter.

View attachment 150224

The rough boring operation went very well. The homemade steady rest is rock solid. The boring bar was overhanging a bit, so I decided to remove the steady rest for the last couple of passes. A very sharp broad nosed tool left an exceptionally clean finish.

View attachment 150225

Next time we’ll drill the bolt patterns.

Take care, Bob.
I thot that was a Grizz in these photos. I had the same problem with the Grizz I have, a G4003G, in which the steady is too small for about half the time I need a steady. I've been intending to build a bigger one. I likes your simple one. What kind of problems did you encounter in making the base/way?

That is a nice steady rest.

.

Lets do a quick calc for the 5A.

P = 40 psi (an assumed number that may or may not be accurate)

L = 2/12 = 0.166666

A = pi * 2.25/2 squared

N = 300 rpm (assumed value)

Horsepower (indicated) = (2*P*L*A*N) / 33,000

{ 2 * 40 * 0.166666 * 3.97 * 300 } / 33,000 = 0.48 hp (indicated)

.
Where do yhou get that L=2/12? the stroke is 2". Did yhou mean 2.12? Also, I used 100 psi not 40 (that's fine tho', whatever one intends to use). and I use 100 rpm.

PLAN = 2 * 1.124^2 * pi * 2" * 40 psi * 300rpm = 5.78HP

doing it my way:

PLAN = 2 * 1.125^2 * 100psi *100rpm * 2"= 4.82 HP

The "mean effective pressure" is not the same as the pressure in the line to the engine.
I forget all the in's and out's about it.

I can't recall why the division by 12.

I had this all written out, and now can't find it.

I am assuming that if the 7" bore and 10" stroke engine in the advertisement is 10 hp, and then working the equation to produce that result, is what I assumed as a check.

If my memory was working better I could give a bit more definitive answer, but we are stuck with what is left of my memory.

I am sure Rich knows the correct formula.

.

A bit of musing:
For those who have forgotten their school teachings... (or Europeans, etc. who do not understand inches, feet, and Horse-power) 2/12 is converting 2 inches (written 2") to feet (0.1667') - so Lb-inches (lb") become foot-pounds = engine torque, ('lbs) and when multiplied by rpm becomes the power... in lbs-ft/second (lbs'/s). Add a factor of 2 for "2 power strokes per revolution".
The 33000 is a conversion from lbs.ft/second to horsepower... Remember it now? - Or am I going senile? ( ).
Please be careful of matching measurement units to the formula units.
Imperial Units are the most convenient "real world" units, but "Somewhere back in history" the French developed everything on a base 10 - which we call "Metric" (Meaning "measure" - nothing to do with base 10?). As this was based on the longest distance you can touch with a finger measured from your nose... - Perhaps as close as you may want to get to someone with Garlic breath? Unless you had been chewing Garlic as well? Who knows?
Koreans used Inches and feet, and somewhere along the line decided Korean Inches should be 1/10th of a foot.
I guess Ancient unit decision committees must have decided a foot was 12 inches long, although that is a size 17 or larger!
The Inch was based on the length of a man's thumb top joint. So very easy for anyone to have an approximate measure that fits in the hand! But finding a foot-long pediment is not so easy...
Then in rating engines you need to understand pressure. Power comes from mean pressure difference on the piston, not boiler pressure. Look at a typical indicator diagram and you'll see how it is not easy to define the mean pressure of steam in the cylinder - for power calculations. It really depends also on the use of superheated steam, dry steam, or simple wet steam for the rating - which will be done against a Company or other standard, on a test bench dynamometer, and they'll have a best result for the sales blurb, but nothing you will be likely to repeat.
An indicator diagram for an engine with early cut-off (E), so in the "Efficient" mode, not "full power" mode.
A company may even fudge figures (innocently or not) by using "simple" calculations and a pressure figure that the engine will never see in reality.
Modern Regulations for cars try to make a level - common standard - but even so, VW and Daimler Benz were caught "cheating" Federal by using different software when on test to that used by Joe Bloggs in real life use! -And it cost them many Millions. But I doubt that the casting "makers" (sellers) are bound by similar regulation...
K2

Rather than a Stuart 5A have you considered a PM Research Machines #6 , thats also a good sized engine and as its in the USA you would avoid the high shipping cost . They say the #6 isn't actually a model its a copy of a full size engine that was sold I believe in the late 1800's . I had a copy of a book also from PM research "Tools Machinary and Supplies by Chas A Strelinger Detroit Michigan " and the engine PM reseached copied was sold in the that book.
When I built the engine I changed it by fitting a slip eccentric so it runs in either direction

Don

That is a nice steady rest.

.
Please - - - - would you include a message number?

(Just spent some time looking and I don't seeum!)

Steady rest, see post #23, starting at the 3rd photo down from the top.

.

Musing on the size of the Stuart 54 engine:
https://www.stuartmodels.com/product/stuart-5a-unmachined/The Stuart 5A is a powerful engine from which you can expect many years of dedicated performance. The engine is quite capable of producing 1 1/2 bhp at 100 psi running at 800rpm.
An optional disc wheel,feed pump and reverse gear are also available transforming this model into a superb marine engine.

## Specification​

Bore: 2 1/4 inch
Stroke: 2 inch
Output: 1 1/2 bhp at 800 rpm
Working pressure: 100 psi
Height: 15 inch
Width: 8 1/2 inch
Depth: 6 3/4 inch

Weight: 13.5 Kg
Seems the Stuart 5A is a proper sized engine - as used in some small steam boats (rowing boat sized?) as it has reversing gear as well.
Displacement of 5.8cm bore and 5.2cm stroke gives a double acting engine as 137.4 x 2 cc= about the same as a 275cc twin motorcycle engine...
But 100psi supply steam really only equates to the power from less than 50psi expansion, - like a 3:1 compression side-valve engine around 275cc. for comparison? - So I would not be surprised at a 1 1/2HP rating... (this being the 735(James) WATT horse-power, not 746W electric horsepower?).
https://theuijunkie.com/horsepower-origin/So we have an engine that is 2/3rds the power of a typical mobility scooter electric motor (1.8kW). I.E. good enough for a small lathe?
And 800rpm quoted by Stuart isn't that fast compared to tick-over speed of a 250cc single motorcycle... Just a matter of engine (crank) balance?
K2

Gotcha!
K2

Steady rest, see post #23, starting at the 3rd photo down from the top.

.
Thanks - - - dunno how I missed it!

Human perhaps?

Fellow steamers: Greatly appreciate the discussion about “horsepower”. All good questions and points. Chapter 19 of “Model Stationary and Marine Steam Engines” by K.N. Harris talks about testing engines and shows some dynamometer apparatuses. The Greenly dyno is very interesting. The 5a is probably big enough for real tests.

Martin (tenor) made a comment about casting lugs. There are almost none with this 5a kit. Going to get started on the connecting rod today. The connecting rod is a very over sized casting, fully half the mass machines away. As with most of the castings, there is no way to easily grip it for machining. So, the first step is adding a chucking spigot.

The spigot is a brass ball “Loctite” to a ¼” rod and then “Loctite into the casting. The spigot will machine away cleanly, with no trace. Future me will discover that the brass ball did not fully work as intended. It was the right idea but will get modified later.

The first step is to grip the spigot and machine the shaft and base. Set the compound to achieve the correct taper on the shaft.

The spigot in the tail stock is the same diameter as the registration indent on the big end. At this point I discovered my mistake and turned away the ball to a cylinder.

Put the connecting rod in a dividing head with tailstock support. This allows machining of all sides in one setup.

From this point on, it’s straight forward to finish the rod. Drill and ream for the con rod pin.

Drill clearance holes for the big end. “Buzz” off the tail stock support spigot to match the big end. This looks like a wonky setup, but it worked.

Next time we’ll finish the connecting rod.

Take care, Bob

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