Monthly Archives: November 2011

9: exhausted!

After a long day of modeling and figuring out sweeps and lofts, I finally sketched in the 2 steam ports and 1 exhaust port.

The outline of the ports can be seen in this see-through. The steam ports are fore and aft, with partial horizontal passage.

The front view of the saddle shows the exhaust port originating from the steam chest seat to the inboard center of the saddle (left to right in following picture).

Nothing about this was simple! The exhaust pipe has multiple cross-section shapes, and very organic curves. Both of the steam and exhaust ports are probably a bit of simplification, but given that the CK Holliday itself is a model, the real engine probably has the same “feature”.

This solids rendering shows the recesses of the ports, and the tappings waiting to receive the steamchest.

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More on steam ports

Last time I posted about using a table from Meyer to determine the steam port area. This can also be done from an equation: fractional steam port area = speed of piston in feet per minute X 0.1/600.

To demonstrate this, I updated the steam port worksheet to run the above equation:

Although the DLR runs at about 10mph, I decided to calculate at 15mph to give the engine a bit more headroom. At 15mph the required steam port area is 4.583 sq. in. I’ve chose a 7.5″x0.625″ steam port which equals to an area of 4.213 sq. in. (with semi-circular ends). The 7.5″ length was determined from Meyer’s suggestion that the length of the port be no less than 3/4 X cylinder diameter, so the rest is figuring out the width, which is actually a quadratic equation due to the semi-circular ends.

At 10mph the actual port area is 3.056 sq. in.

So for the chosen steam port size of 7.5″x0.625″ should be able to work for at least 10mph. Let’s see what the exact optimum speed for this sized port will be:

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8: steam and exhaust ports

Most of today’s work was spent revising the saddle and cylinder dimensions and alignments. Rough checks were made from scaling the Lingenfelter’s drawing.

Then, since the guts of the CK Holliday’s cylinder, steam chest, and valve gear are not known. So, to model these details accurately, I had to “re-engineer” the engine some what. Hopefully I follow the same “track” (haha!) as Walt did when building the engine in 1955.

The DLRR line normally travels at 10mph around the park. I assumed 15mph just to have some margins. With some engineering (they’re really just geometry calculations) we can figure out the speed of the sliding valve, knowing that the engine has a 10″x15″ cylinder.

Then, use the table from Meyer to get the steam port size. From the table below, at 350 fpm, the steam port size is 0.058. Plug this value in cell E10, and we get steam port area of 4.55+ sq. in.

Don’t forget to tweak the numbers a little bit to make the dimensions machinable.

And here’s a rough sketching of the steam port on the steam chest seat.

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7: cylinder and saddle

Minor revisions to the cylinder’s dimension.

Started sketching out the half-saddle casting.

Look carefully and you can see the 1 degree rear tilt on the cylinder. This minor tilt allows condensed steam (water!) at the bottom of the cylinder to flow out of the rear cylinder cock. This ensures that there is no trapped water in the cylinder that can cause damage to the assembly.

Rough fitting the half saddle onto the frame:

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6: cylinder

The 10″x15″ cylinder is made with 3/4″ bolts “caps” at each ends.

The front and rear caps are temporarily identical. The rear cap is of course supposed to receive/host the valve gear hardware.

A lot of work to do for this part, because the cylinder will be “made” with half-saddle as cast-in-one as it is the common practice in fabrication (and therefore presumably the CK Holliday was built following the same practice).

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5: driver axles

The 5.5″ driver axles are fitted into the axle boxes. Its dimensions are somewhat temporary until other parts (wheels) are fitted. The forward axle is temporarily identical to the aft axle right now until the eccentrics are fitted.

Here’s the frame compared to the original drawing:

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4: axle box fitted

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