Thursday, June 23, 2011

Rail curvature

From: A2lindner@aol.com

I have been reading George Kraus's book High Road to Promontory and am at the part where the Central Pacific laid 10 miles of track ... in a single day. Kraus mentions there was difficulty where curved track had to be laid as the rails were bent by hammering them between two blocks (page 252). I'm nor a railroader or engineer but I have difficulty with this. First, if the iron (56 lb./yd. I guess) was soft enough to be bent by hammering, would not the place where you hammered be damaged/distorted? Second, how could you have any accuracy-keeping the curvature smooth and the correct amount of turn?

—Al Lindner


Hart stereoview #333, detail
Hart stereoview #333, detail. CPRR.org

6 Comments:

Blogger CPRR Discussion Group said...

From: kylewyatt@aol.com

The rail was hammered in a number of spots in order to create a smooth curve, not just at one spot. See Hart photo #333. And with experience, a smooth and correct curve could be readily made.

—Kyle

6/23/2011 6:52 PM  
Blogger CPRR Discussion Group said...

From: A2lindner@aol.com

... Yes, that would stand to reason. However it must have been pretty difficult to achieve anything resembling a smooth and correct curve. I'll have a good look at the photo, they also must have had some way to prevent distorting the rail at the places they were pounding on it if it were that soft.

6/23/2011 9:35 PM  
Blogger CPRR Discussion Group said...

From: "Wendell Huffman" wendellhuffman@hotmail.com

Pre-bending rail for curves was standard track-laying practice of the day. Rail is flexible enough that it will lay in place with a curve of 3 or 4 degrees, and there is some inconsistency in the books about how sharp a curve needed to be before it was pre-bent.

To bend rail, a piece of rail was placed with its ends resting on timbers set across the rails of a section of completed track. Men then bore down on the middle of the rail with levers hooked under one of the fixed rails of the track. Published tables of ordinates showed exactly how much bend to put into rails of a given length for curves of various degrees of sharpness. The deflection could be measured against a string line stretched along the rail, and a string can be seen in a good copy of that Hart image Kyle submitted. But with 1,013 curves in the 690 miles between Sacramento and Promontory (amounting to over 277 miles of curved track), the experienced crews probably could bend a piece of rail pretty well by eye and feel. When the deflection was just right, other men beat on the rail with sledge hammers to set it. The bending was done with the levers; the beating on the rail with hammers was merely to "set" the bend. The CP used this method from start to finish. The Sacramento Union described this method being used when curve No. 1 was laid at Front and I streets in Sacramento in October 1863, we see it being used in that Hart photograph, taken in November 1868 in Palisades Canyon, and we know track laying slowed on the afternoon of 28 April 1869, when they had to lay curves.

By the way, the CP was built with circular curves. The earliest evidence of transition spirals does not appear until 1876. The Southern Pacific continued to pre-curve rail at least until 1900.

Another issue with curves was the need for short rails.

[continued below]

6/23/2011 9:47 PM  
Blogger CPRR Discussion Group said...

Again following standard practice of the day, the CP built their track with "square" joints, that is, the rail joints were kept directly opposite each other. As rails on the inside of a curve gain 1.03 inches per 100 feet per degree of curvature, joints quickly get out of square on curves. When they first started out in 1863, crews had to cut a few inches off the ends of the inside rails in the field. Later, the company ordered a certain portion of their rails six inches shorter than standard. When the inside rail had gained three inches, a short rail was laid. This way the joints were never off by more than three inches one way or the other. On ten degree curves – the sharpest permanent curves on the CP – every other inside rail would be a short one. The beginning and ending points of each curve was indicated by a stake marked with the curve number and its degree of curvature, so it was not difficult to determine just how many short rails would be needed.

Joints could either be "suspended" or "supported"; that is, the joints were either directly between two ties or centered on top of a tie. The odd thing is that written descriptions of CP practice indicate suspended joints, while supported joints show in a number of Hart photographs. As the joint tie was set first, a single joint tie for a supported joint would make faster work, and I suspect the supported joints were adopted for speed. East of about Brown's the CP was (for the most part) laid with 30' rails. Ties were initially set every four feet, with the intervening ties inserted after the rails were set. (Again, this was done to save work and time, since the intervening ties could be distributed by train rather than wagon.) But, with 30' rails, ties set every 4' doesn't work out evenly. In several Hart photos, the odd 2' spacing at the joint is apparent. "Square" joints went hand-in-hand with bending rail. Once railroads adopted staggered joints they discovered they did not have to bend the rails as the "continuous" adjacent rail strengthened the joint.    

There is an odd issue with the curves laid in that 10 mile stretch laid in one day. Track length was measured from one engineering station to the next, spaced 100' apart as measured with a surveyors chain. In other words, the measurement around curves is made with a series of straight lines (chords). This distance is actually shorter than the line following the arc of the curve, and thus the 10 miles and 56 feet laid that day is likely an understatement of the actual length of rail laid.

—Wendell

6/23/2011 9:47 PM  
Blogger CPRR Discussion Group said...

From: "RANDALL HEES" hees@astound.net

Several thoughts;

1) Don't over estimate how hard a practice is, or under estimate their skills. Having worked with 19th century railroad equipment, I have seen and done things like installing truck bolster truss rods (put in red hot, and bent to shape as installed) that I could't imagine were possible until I tried. Properly fitted and installed joint bars lock the rail ends so that they act as a single piece.

2) Rail is much more flexible than you would expect. Using joint bars or fish plates (which CP was by 1869) you can simply make the joints, several joints ahead, then bar the rail around into graceful curves. I strongly suspect the bending was mostly associated with earlier "chair" rail joints which only hold the two rail ends together.

—Randy Hees

6/24/2011 8:52 AM  
Blogger CPRR Discussion Group said...

From: A2lindner@aol.com

Seems like I really stirred up a lot of activity here-good! Anyway I appreciate any chance to learn new stuff. I don't believe I ever heard of truss rods before, just chairs (which sound inferior to fish plates) and fish plates. There's a lot of technique here requiring a lot of skill, huh? Having read a bit on the subject, it just seemed to me that some authors had never done much in the way of things manual.

—Al

6/24/2011 12:29 PM  

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