Introduction
I describe here some broad practical steps in making an acetate spectacle
frame by hand. For a brief comparison let's consider the way acetate frames
are often made. In the spectacle industry the typical factory set-up involves
dozens of pre-set routing and heat-forming/embedding machines to produce
each frame design. Designs must be guarranteed of commercila success to
pay for this huge set-up cost, and must fit into the parameters of the
machinery. Making by hand has all the attributes and advantages that a
factory cannot afford: greatest flexibility of design, quickest speed
of reaction to customer/market requirements, and total uniqueness. The
downside is that handmade frames take time to make, the runs are small,
and the maker must be skilful. Sound familiar? Let's press on undaunted
anyway; the rewards are fulfilling.
 
The basic drawing, and a photo of a finished
acetate frame.
I'm assuming prior knowledge of where and how the frame is to basically
sit on the head to allow the frame-held lenses to be propped in front
of the eyes in a relatively comfortable manner. Frames can have nose-pads,
temple-tips, hinges. Or they can have none of those. As a designer you
might like to question and redesign these. But ultimately if a frame is
to be worn for a time comfort will be a major design factor. If any of
you are spectacle wearers, you'll understand about daily comfort.
But then again you may be making a frame for short-term use, and will
be satisfied with minimal features for fitting the frame.
Another assumption I'm making here is about suppliers of acetate sheet
and hinges and other useful spectacle parts. I may in the future be called
upon to write a Suppliers listing. My own suppliers are necessarily local,
so it may well be that if some of you were to contribute to a pool of
spectacle/optical suppliers information I could collate a full listing
that would be useful world-wide.
Acetate for spectacles
Cellulose acetate comes in sheets of various thicknesses - 3.5mm to 6mm
or more. The type we used on the spectacle-making workshops here in January
'96 was donated by a small New Zealand factory. It is made by a manufacturer
in Italy and is produced by them in a variety of transparent, opaque and
variagated designs. This from the manufacturer's information pamphlet:
"Cellulose acetate has a good resistance to water, low concentrations
of acids, bases, and inorganic salts, parraffinic hydrocarbons, high m.w.
alcohols, oils and fats. In contact with boiling water some whitening
can arise. Soluble in ketones and esters. Soluble in ketones and esters.
Strong acids and bases, pure or concentrated oxidising salts, can cause
chemical degradation. ... As regards the continuous use in contact with
skin, typical in the use of spectacle frames, it is possible to note the
following: there have been cases of contact dermatitis, generally coused
by excessive pressure with consequent mechanical abrasion; these cases
are not frequent and are of limited seriousness, which normally recede
of their own accord often simply by re-adjusting the frame. The substitution
of the frame with one of different composition is rarely necessary. None
of the components of this acetate sheet is a source of frequent or significant
irritations to the skin at least under normal conditions of use. As in
the case of any plastics material or metal, we cannot exclude an exceptional
reaction, which could necessitate the substitution of the type of material."
 Vee-routing
the lens groove in acetate sheet - instructor Brian Adam. Spectacle-making
Workshop, Baltimore MD, June 1996
Hand-making method
Here I'll describe a fairly traditional hand-making technique where the
acetate sheet is cut, shaped, heat-formed, and solvent-welded. By 'traditional
hand-making technique' I mean a series of steps that most "object-makers"
would be quite familiar with - jewellers, modellers, sculptors, etc. This
acetate sheet I speak of may also be two or more different-coloured sheets
fuse-laminated together: solvent-fusing sheets together without trapping
air bubbles is very difficult, so I recommend restricting your first attempts
at laminating to small sheet areas.
Cut your shape from the acetate sheet
Use a jewellery saw with a wax-cutting blade
Weld together any joints
You might be building up layers, making corners, adding nose pads, adding
contrasting colours. Wet the parts with acetone solvent and hold with
light pressure for 20 seconds and leave for 24 hours to cure
Heat-form
Curve parts to fit the face - little 'bumps' for the bridge of the nose,
corners, shaping to suit the lens curve. At 110°C - 130°C (230°F
- 260°F) the 'plastic memory' is overcome and reset to a new shape.
Otherwise the acetate will try to return to its original shape (ie the
shape that was previously set at over 110°C) Heat source: 50/50 water/glycerol,
moving air, or hotplate
Cut the lens groove 90° - 110°. Rout with a vee-cutter, preferably
with a limiting device attached, to ensure the vee is cut about 2mm from
the front face - I have used a fairly standard 90° hart burr with
some success.
File and sand With enough time the solvent-joins will be as solid as
the sheet base. Use carving and engraving tools and a succession of rasps,
files, emery paper to get the surface you want
Finish
Buff polish (slowly), tumble polish, or solvent-polish
Fit hinges
Make your own from acetate and fuse them on, or fabricate from another
material and rivet, or heat-embed your own or standard-supply parts
Sunglass lenses: cut the lenses
I use hard resin opthalmic lenses (98% UV blocking), 'plano' (no correction).
I cut with a jewellery saw (3/0 blade), file and sand an edge bevel
Dye those lenses
Dip in water-soluble lens-dyes, or hot fabric-dyes
Pop the lenses in
The lenses should be ever so slightly oversize. The frame is first softened
(to about 70 - 90°C) by hot air, water, or a tub of hot salt
Frame adjustments
Adjustments for different heads are usually made by bending or filing.
Bending: the acetate should be heated to at least 110°C to make a permanent
change to the plastic memory. Filing: adjustments are made by filing small
amounts from the temple/sidepiece at the point of the hinge-stop so that
the hinge opens out wider.
Can these hand made frames accept your prescription lenses?
If the eye-rim has a reasonably deep and straight vee groove cut in it
for a lens then almost any type of prescription lens may be fitted by
a dispensing optometrist that is willing to hand-cut the lenses.
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