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Constructing a rope from strands - selecting strand sizes


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I was beginning to think about getting/making the correct size ropes and cables for my project.  It occurred to me that if I want a certain size finished cable then how do I select the diameter of the strands used in the cable?.  There doesn't seem to be any data or formula available for this.  I guess most ropewalkers have developed their own by trial and error.


I started making a drawing of a 3 strand rope to see the relationship if the strand were assumed to stay circular.  I then took the 3 strand rope and used that to make a larger 3 strand cable (now made of 9 strands).  Have a look at the drawing in the attached  pdf.  


I then tried to figure out how the helix angle (lay angle) of the rope affects this.  As a quick simplification I assumed that this reduced the diameter by the cosine of the angle.  Based on my model, a rope made up of three strands of diameter d and a helix angle of A will have an outside diameter of 2.155 x d x Cos(A).  Or, for a 9 strand rope,  [2.155 x Cos(A)] = 4.64 x Cos2(A).


Theory is good, but it needs a reality check, so I measured some ropes and string around the shop.  The rope measurements and the calculated results are tabulated in the attachment.  It turns out the formula works quite well.


The numbers I have are for fairly large size ropes, not model size.   If some one could measure some of their home made rope, or try to use the formula to make a given rope size, that would be a good test.  Also, if anyone had access to actual cable (say a 6" hauser), that would be very interesting.  


I can update the table or refine the formula as needed.


If this works, I could try stroud layed 4 strand rope.




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Hi Bruce:


You can measure the diameter of thread or made rope by the following:

1. Make a measuring stick by cutting a 1/2 inch slot in a straight piece of wood.

2. Wind the rope tightly around the measuring stick, staying within the ½ inch slot.

3. Make sure the winds of the rope are snug against each other without overlapping.

4. Count the number of turns as you wind it.

5. The diameter is calculated with the following formula:

            Diameter = 1 / (# of Turns * 2)


I use DMC Cebelia thread, and it is graded by size (10 is largest, 100 is smallest), and made up the attached chart by making and measuring rope.


Hope this helps,


Happy Holidays






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Thanks for the posting and the chart.  A quick check shows that my formula works for the 3 strand ropes.  


In you post you say Cebelia, but the chart lists Cordonnet.  Could you clarify?  Is one a better quality for rigging, or?




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I don't dye big batches of rope yet. So far I've only done a few strands at a time. That being said, I use an eye dropper to measure the proportions of the ink into a small jar big enough to take a coil of rope, then add an amount of isopropyl alcohol equal to the total amount of ink, mixing everything with a small stick. I wind the rope into a loose coil, submerge it in the ink for 5 minutes, then uncoil it and draw it through a paper towel to remove the excess moisture. Hang to dry.




You caught me! I meant to type Cordonnet. Here's a link to a source:





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I found "Treatise on Rope Making - Description of the Manufacture, Rules, Tables of Weights, etc." by Robert Chapman  (Master Ropemaker of HM Dockyard, Deptford), 1869.


The topics start with harvesting hemp, twisting fibres, spinning, tarring, amount of yarn.threads for various sizes and types of cable, sizes of hearts, weights of cables by length, It even covers manufacturing costs, by operation, including management (officers)


Although published in 1869, the English seems older (it is a revised edition), and there is a lot of jargon that will take a while to decipher.  The method of showing calculations is not easy to follow.  Not an easy read, and not a place to find quick answers.  



Download of pdf, eBook and other formats from the Smithsonian.  




This is probably a candidate for posting in the References list.



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Salute Gaetan,


I've seen the post.  My interpretation is that It covers the number of threads of a given diameter that make a strand of a given diameter.  I covered the next steps:  the diameter of three strand rope for a given strand size and the diameter of a cable made up of three ropes.  For instance, I can make a rope using three strands that each have have 25 threads.


If you get a chance to look at the Chapman reference, he talks about a progression of sizes, starting (I think, haven't got it all straight yet) from threads and yarns, which are spun, then moving up to ropes, which are twisted (as on a ropewalk), then larger ropes, which are twisted from several ropes.  


As modelers, we'll have to decide, depending on the scale we're working and the amount of patience, what will be the fundamental fibre to start making our ropes.  I see on another post that someone what trying to start the process from 100 or 120 cotton thread.  Another was pulling apart threads and using the smaller "yarns" that make up thread.






PS.  I've just found another old book on rope making:  "ModernFlax Hemp and Jute Spinning and Twisting"  by H.R. Carter 1909.  



I hope it will clarify the definitions of yarn, thread, lessom, etc.

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  • 2 months later...



This topic and your table of sizes and colors will really help me to fine-tune colors. My Byrnes ropewalk

was delivered a few minutes ago, and the experimentation will begin with a head start from you. Thank you, and I

will post any useful outcomes here and on the Lauck Street site. As ChuckL (on the LSS site) said recently,

we are "standing on the shoulders of giants."



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