Armillary Equatorial Dial

By Jackie Jones

Some time ago I made some small dials for a local exhibition; the idea was that they demonstrated different types of dials.  

This one is an armillary equatorial dial made from an embroidery frame.  These are two concentric hoops, normally made of plywood and are available in a number of sizes.  I used quite small ones, about 10 cm diameter. 

The layout is not complicated; circles the size of the hoops were drawn on paper and 15° hour lines marked.  The hoops could then be laid on this for marking.  On the inner hoop, all the hours from 6am to 6pm were marked plus a cutting line before and after the hours.  The cutting line was marked on the outer hoop plus the noon mark and the two sixes.  The exact hour positions were made with a small file and then marked with numbers from some Letraset rub-down lettering; the noon position had a hole drilled for the fixing screw. 

On the outer hoop, holes were drilled at the 6am and pm marks to take the gnomon cord and a small hole at the noon mark for the fixing screw.  They were turned at right-angles and screwed together.  The gnomons I used were different, on one a cotton embroidery thread with a fish shaped bead to keep it taught and on the other a heat-blued titanium wire.

Using the curve of the outer frame as a template, a piece of plywood sheet was cut to form a stand and another piece fixed with a cross-halving joint to keep the dial steady.  Accurately measuring to ensure the gnomon was at the angle of the latitude where the dial was to be used, the base and dial were fixed together with a small screw.  It was all finished with a layer of varnish to help preserve the wood and Letraset.

Easy to use; just place on a horizontal surface facing south and read the time indicated by the gnomon shadow.