String lining curves

[Bricketts]

Trying to get a better understanding about string lining a curve, hoping someone can explain in layman's terms, here are my questions and what my understand is. (Question 1) When you measure a curve (string line) how do you find what the design of the curve is? My understanding is if you string line a curve and your measurement in the full body of a curve is 4 inches is that a 4-degree curve?  (Question 2) Now if I want to find the deviation between the full body of the curve and what I actually measured, do I subtract my measurements from the 4" by design to get the difference between the two?  for example, I take a measurement of 3 1/2" do I subtract the 3 1/2" from the 4" by design?  if so, is the deviation between the two 1/2"?  Any help in opening my understanding would be greatly appreciated. 

Thanks

[BigDaddy]

to the Forum.  Your posts will be delayed in moderation for a bit. 

I've been in the hobby 40 years and I know what a stringline derailment is, but that is not what you are asking about.  I never needed to know that.

Somebody will know, I'll bet GregC knows.

[selector]

They used 100' chains to measure tangents at one time.

Top 4 Linear Methods of Setting out Curves | Surveying (engineeringenotes.com)

[doctorwayne]

Bricketts

(Question 1) When you measure a curve (string line) how do you find what the design of the curve is?

The 4" string is the radius, not the curve itself, and such a curve in HO scale would be unuseable unless your rolling stock (or loco) was on a single four-wheel truck.

The minimum mainline radius on my HO scale layout is 30", but I have several wider curves in the mid-forty inch radii.

Wayne

[kasskaboose]

What does string lining a curve mean?  Is the OP trying to measure the radi of a curve?  Why am I confused?

[doctorwayne]

kasskaboose

What does string lining a curve mean? Is the OP trying to measure the radi of a curve? Why am I confused?

Yeah, I found the OP's input rather confusing, too, with the terminology being somewhat vague.

Wayne

[gregc]

Bricketts

(Question 1) When you measure a curve (string line) how do you find what the design of the curve is? My understanding is if you string line a curve and your measurement in the full body of a curve is 4 inches is that a 4-degree curve?

do you mean degree of curvature which is the angle of a curve marked by a 100 ft chord between 2 points on the curve (see figure in link)

 degree  1:1(ft)    O(in)    S(in)   HO(in)    N(in)
      5   1146.3    286.6    214.9    158.1     86.0
     10    573.7    143.4    107.6     79.1     43.0
     15    383.1     95.8     71.8     52.8     28.7
     20    287.9     72.0     54.0     39.7     21.6
     25    231.0     57.8     43.3     31.9     17.3
     30    193.2     48.3     36.2     26.6     14.5
     35    166.3     41.6     31.2     22.9     12.5
     40    146.2     36.5     27.4     20.2     11.0
     45    130.7     32.7     24.5     18.0      9.8

 

 

[mbinsewi]

Following.

New one on me.

Mike.

[maxman]

Stringlining of railroad curves:

https://www.arema.org/files/roadmasters/1995/1995_STRINGLINING-OF-RAILROAD-CURVES.pdf

 

[doctorwayne]

Too much baffle-gab for me...get some flex track, and stick- or nail-it-down in whatever curves or straight sections that you prefer.
If you pay attention to what you're doing, it should work out well enough for you to be able to enjoy using it.

I did my layout without bothering with sketches or track plans, and it worked-out good enough that I can still enjoy it.

Wayne

[wjstix]

It might be better for the OP to post this over on the Trains mag forum, since what he's talking about is something (apparently) used for real trains rather than models. 

[mbinsewi]

doctorwayne

Too much baffle-gab for me...get some flex track, and stick- or nail-it-down in whatever curves or straight sections that you prefer.

Yep.  Exactly.

Also agree with Stix.

Mike.

[BigDaddy]

deleted.  looking at the pdf. they appear to be taking a measurement in inches on a real track. 

[gerhard_k]

Thank you, maxman, for this link to the 'real railroad' measurement.

While, as others have pointed out, it's all overkill for our models, I found it fascinating from a technical and intellectual standpoint. (I also found the OP's question phrasing confusing, but it all worked out).   

[fwright]

And here I thought the OP was talking about "stringlining" on model curves where a train derails to the inside of a curve.

Fred W

[Bricketts]

Thanks all, I am apparently on the wrong forum, I am speaking of real trains thanks for your all responses. 

[Bricketts]

Thanks maxman great info.

Bricketts

[Nil]

maxman

Stringlining of railroad curves:

Thanks from me, too.  I am puzzled, though, that they consistently used the outer rail without reference to why it was chosen over the centerline or the inner rail. 

I would have to assume that they felt that the miniscule increase in accuracy would simply not be worth the effort.  Still, discussion would have been helpful.

[Overmod]

The outer rail is used because you're measuring along the gauge corner, directly along a rail.  The gauge corner on the inside rail is convex across where the measurement would be taken...

For model work, you'd almost certainly use an appropriate scale rule, or a tool cut to scale length with precise corners ... although the precision of the cross-measurement is the critical thing, and if model railroading involved true scale curves you might need to include a screw micrometer head for the necessary precision 

But curves on practical layouts are 'selectively compressed' and transition spirals dramatically abbreviated, and one-piece curve templates are probably a better solution for both.