Apr. 15, 2007.
John R. Bentley 2007.
A Naphtha Launch Engine
- in miniature -
Under construction from the 1887 Patent Drawings of Frank W. Ofeldt
(and various other illustrations)
Apr - Jul 2018: Changes are currently being made to this model!
Constructing the Model
I hope these will show some detail - I will be adding and replacing as construction continues.
Here are the very first four pieces of the engine at the begining of construction.
The side pieces temporarily propping each other up.
This is my first tangible indication of the size of the model.
Immediately after glowing red hot during the silver brazing process.
It is really not quite as bad as it looks!
A quick cleanup helps!
Note that a bottom flange has been cut from the same .0625" brass sheet.
Here both the top and bottom flanges are temporarily sitting in position.
Fluxed and sitting on a firebrick ready to be silver brazed.
Small bits of Easy Flo 45 are in position at the bottom flange joint.
Now here's a thing of beauty!
(It will clean up in an acid bath)
The round bosses on both sides will be drilled and tapped to become the exhaust connections.
(the T-shaped bar at the front is for mounting the timing idler gear)
Curving a piece of .034" brass sheet for the crankcase.
This curved sheet will form the bottom.
The crankcase flange was cut from 3/16" Naval Brass.
The flange will be milled to proper thickness later.
The crankcase ends were made from this disk, cut from a real boat's propeller shaft.
Aren't those 4"x 6" bandsaws the greatest invention!
For silver brazing, these semicircles were temporarily fixed to the flange.
Small sacrificial brass screws were used. (underneath in this view).
Two more holes to temporarily hold the crankshaft main bearing supports.
The main bearing supports.
Everything was silver brazed at the same time.
(including a mounting pad for the thrust bearing, protruding at the top)
Hollowing out the bearing supports with the Taig Micro Mill to reduce unnecessary weight.
(this also allows for a thrust connection between the engine and hull if necessary)
Below: The valve plate.
Valve ports will be milled into the three pads to communicate with the
cylinder tops and the exhaust space beneath this plate. In operation, the
slide valves will be moved across the port faces by an overhead camshaft.
The valve plate in position on top of the cylinder block.
(temporary screws were used during this phase and later replaced with scale studs)
This is the embryo valve cover.
Simple silver brazed construction.
An unfinished flange beneath the valve cover.
The flange is notched to allow good contact with the front camshaft bearing.
A thick plate integrated into the top forms a flat and strong
surface on which the vapor generator will be mounted.
After silver brazing.
Two "ears" are yet to be added on either side to attach the pressure gauge syphon and safety valve.
Facing the top surface on the Taig lathe.
Below: Finishing the gas generator mounting pad and connection.
A nipple screwed into the central hole will connect the gas generator
(naphtha boiler) to the top of the engine's valve chest.
The three cylinders hang from the valve plate, which is "sandwiched"
between the valve cover and the cylinder housing top flange.
Notice here that the "ears" previously mentioned have been added,
but are not yet drilled and tapped for the pressure gage and safety valve.
The finished valve cover which also serves as the vapor chest with full operating pressure inside.
Below: Two of the timing gears have been added.
A third gear and handwheel attached to the camshaft extension at the top of the engine.
At this writing (mid April 07) I can only imagine how the
engine will look when painted in black or a very dark color.
This picture was processed with strong contrast in order to help visualize how it may appear.
Here the concentric coils of the vapor generator are visible in position.
When completed, the casing and stack will hide this interesting feature.
this unusual powerplant, including the special Naphtha Launch propeller.
These can be viewed on the following pages:
Cylinders, Pistons and Rods
Valve Operating Wheel
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