Proportional Calipers **

Sometimes I need to make my  own drawings of seashells.  Not easy if one does not have the artist's eye to measure exactly.  I tried to make my own proportional calipers and developed several versions.  Then I googled for them - and one can buy them, made in metal or other material.
Here is the simplest one:-
You can loosen and tighten the wing nut and bolt.
You can enlarge the sketch as shown.  Click on images to see them more clearly.

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Here is the best most accurate one I made.  This is cardboard template first,  then one can make it with wooden ruler or whatever length timber you wish.  The cardboard is too wobbly to use.

Diagram describes proportionality.

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Longcalipers.eg.

This model is not accurate at large sizes.  The pincer tips make the error.

I think it is better to make a caliper dedicated to one proportion only, eg  x8.  This is the one used by sculptors who make enlarged final sculptures  x8 times the size of the original maquette.  

I got the idea when I saw Tom Bass' retrospective Exhibition at the Sydney Opera House, some years ago.  His instrument was  expertly and elegantly made in wood and brass. 

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Here is my attempt to model the tip of a seashell:-

The calipers shown were fairly but not really accurate.  

The tip of one pincer broke off and I had to try to glue a bit on to fix it.

Measure the width of the whorls, north, south, east and west.  It made a flat diagram. 

 To make it a cone,  find the height and put a similar cone underneath, and slit the sides all around to make the cone.  Stickytape it together. Next I have to figure it out lengthwise so that I can plan how many crochet or knit stitches are needed to make a more accurate tip to my seashell models.

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