Charles wrote
>if the hole that passes the light is on the outer surface of the ring and >the hour lines are on the inside, would this not then introduce an error? >Emerson's diagram indicates the inner and outer diameters to be the same. > Any thoughts on the effects of ring thickness? Why not 'countersink' the hole so that it is reduced to an 'edge' at the inner surface of the ring? > >Regarding physical construction: > Does anyone have any idea how to form a flat strip of brass into a perfectly circular ring >without damaging the engraving on either side of the strip of brass? Ideally you could take it to any metal workshop or bench jeweller who has bending rolls. If not you can bend it by hand around any hard cylindrical object but make sure you anneal the brass first to make it pliable. This will avoid localised 'peaks'. Heat to a dull red on a firebrick and allow to cool naturally or (quench in water). The metal will then bend easily but will 'work harden' increasingly with any alteration in shape. Repeat annealing will soften it again but avoid prolonged heating which builds up oxide. Bend a strip which is longer than you require into a helix (like a short coil spring) in order to obtain the correct curve at the ends (almost impossible with a strip cut to finished length). The longer the strip the easier the bending! After cutting the surplus ends off the helix can then be flattened out into a circle and the joint squared up with a fine file held in the gap while the ring is gently squeezed in the hand. Silver solder will then make an almost invisible joint after which a 'pickle' in 10% sulphuric acid and fine abrasives will remove oxide and flux. The ring will remain soft after annealing/soldering but can be 'work hardened' again by careful striking with a wooden/nylon/leather mallet when rotated on a polished steel bar. Any blemishes on the mallet face or the bar may be transferred to the brass. Try it all out on scrap material before working on your engraved material. Tony Moss
