Measuring Rope diameters

[Mike French]

Has anyone a good method of measuring rope diameters  I have several sizes but I need to measure for scale and a dial gauge doesn't really work.  

Mike

[mtaylor]

Basically, the easy way is wrap the line carefully around a dowel (ten turns) then measure the turns and divide by 10.   So if the measurement of the 10 wraps are say 1 inch, then rope is 0.10 inch in diameter.  

 

There's a good discussion starting here: 

 

 

[druxey]

On the other hand, rope is usually measured by circumference. A fair approximation is to wrap 3, 6 or 9 turns and measure across, then divide this measurement by 3 as appropriate. (Rope circumference to diameter is a factor of 3.1416.)

[Gregory]

In what context is it measured by circumference?

All the rope I can find for sale seems to be listed with diameter and length.

 

E-rigging for one example..

 

The rope I'm mostly working with right now is about .6mm in diameter..  I'm not sure how knowing the circumference would help me at this point.

Edited May 29, 2019 by Gregory

[allanyed]

Gregory,

In days of old, rope was given in circumference, never diameter.  Move forward a couple hundred years and modern day suppliers use diameter.  If you look at contemporary rigging tables, the dimensions will be the circumference, so beware if you are using them as a guide and order the rope diameter based on the circumference dimensions.  You will have rope that is 3.14 times larger than it should be.   

Allan

[druxey]

Also, irritatingly, 0.6mm diameter is not helpful when one is working in a feet and inches scale! On needs to make a metric-to-duodecimal conversion, then factor in the proportion (e.g. 1:24 scale). Aaargh!

[Gregory]

Why do I suspect you are messing with me? 

 

I'm a " if it looks good, it is good " kind of person...

[druxey]

No, I wasn't messing with you, Gregory - it's the rope manufacturers that supply line in metric that are!

[Roger Pellett]

That is why it is helpful to make up a table of rigging sizes ahead of time.  With an Excel spread sheet you can add a factor to each column and work your way across to the final scale diameter.  

 

I made a simple stepped gage from two sizes of dowel with marks at 1/8” and 1/4”.  For example, the diameter of line where 10 wraps touches the 1/4” Mark is .25”/10 or .025”.  Each available spool of line is marked with the number of turns per 1/4”, and the last column on my rigging table is also tabulated in the same way so at my workbench it is simply a question of using the spool marked with the correct number of turns.

 

Roger

 

 

Edited May 30, 2019 by Roger Pellett

[RichardG]

7 hours ago, druxey said:

Also, irritatingly, 0.6mm diameter is not helpful when one is working in a feet and inches scale! On needs to make a metric-to-duodecimal conversion, then factor in the proportion (e.g. 1:24 scale). Aaargh!

Interestingly I've been building software to do that. I have a working desktop version that I'm slowly converting to an Android app (in my not very abundant free time). This is a screen shot:

It supports English (in/ft in/yd ft in), metric (m/mm), and French (Peid/Pouces/Lignes). 

The scale can be set on both sides (so you can go from 1/24 to 1/64 for example)

 

More samples:

I've been doing this as an exercise and for personal use. I could make it available if people are interested (it would be free).

 

Thanks,

Richard

[mtaylor]

For the French, are you using the current measurement or the one they used back in the period?   I'd love to see the desktop version as I don't have phone that runs apps.    

[RichardG]

Back in the period (18th century). Numbers were taken from here: https://sites.google.com/site/shipwrightsfaq/smf-researchnotes/smf-RN-Cross-CulturalHistoricMeasurementUnits

 

 

[Mike French]

Thanks fellas .quite an interesting array of answers . I am currently building the HMS Unicorn and am about to start rigging. Corel did not supply the cordage with any sizes marked and as a novice I have had to try and work it out. Thank you Mark you method appears to work in the parameters that I am using. I work in metric Mike 

[mgdawson]

14 hours ago, Gregory said:

In what context is it measured by circumference?

All the rope I can find for sale seems to be listed with diameter and length.

 

E-rigging for one example..

 

The rope I'm mostly working with right now is about .6mm in diameter..  I'm not sure how knowing the circumference would help me at this point.

By convention, when measuring rope in imperial units use circumference, when measuring in metric, diameter.

[druxey]

Richard: your app looks like a great one. If available, I imagine a lot of folk would use it!

[RichardG]

I'll create a setup package and instructions for it and make it available.

 

Sorry for diverting this thread

 

Richard.

[wefalck]

9 hours ago, mgdawson said:

By convention, when measuring rope in imperial units use circumference, when measuring in metric, diameter.

Actually not.

 

Laid rope was always calibrated by circumference, whether you work in imperial or metric unit. The reason is very simple that any other method would give differing results depending on where you measure - just try this with a vernier caliper and turn the rope: the measured diameter will change as you turn it. You could use a gauge with holes, but keeping such gauge e.g. on board a ship would be inconvenient. It was easier to wind a thread say ten times around a rope and then measure its length, divided by ten it gives you the circumference.

 

When wire rope and then later braided fibre-rope came into use, measuring diameters became physically possible. However, well into the 20th century wire rope was sold by circumference.