Accurate cutting

Cutting glass pieces accurately is a matter of practice whether done by hand or by person-guided machines.  Computer guided machines rely on accurate instructions being given to it. This is mainly about human-guided cutting with some information on saws.

Hand Cutting

The right approach to cutting is necessary to accuracy. 

• ·        You need clean flat surfaces with only a little flexibility, with no glass shards, bumps or warps that would make scoring the glass more difficult. 
• ·        You need to work at a comfortable height – usually about 10cm below your elbow. 
• ·        You should be moving your torso and sometimes your whole body to score, following the cutline.
• ·        Your elbow should be at your side and your wrist should be fixed. 
• ·        You need to work at a corner of the workbench to be able to move your body around as you follow a curve.
• ·        Your cutter should be at right angles to the glass (side to side)
• ·        The cutter should be angled back toward you slightly, so you can see down the barrel to the scoring wheel.  Also, so any unevenness in the glass will not cause the cutter to stall.
• ·        The pressure should consistently be about 2.5kg or 7 pounds. Do not listen for the sound, as it varies between opalescent and transparent glasses.  Heavy pressure on any glass causes unwanted break outs. Score to the pressure, not the sound.
• ·        Keep a consistent speed. Variability in speed also translates to uneven pressure. Even when you could go fast in scoring, keep to a steady pace.
• ·        Score and then break each line before going on to the next.  Do not score all around the piece in one go. It does not allow for any adjustment, if the cut is not accurate.

Oil filled cutter in classic hold

These approaches to hand scoring apply to all the ways of assisting accurate cutting.

There are at least three methods to assist accuracy in addition to the basic requirements, which apply to any method you use. 

• ·        My preference is to score the glass directly over the cartoon. This involves no extra pattern making.
• ·        Drawing the lines from the cartoon on top of the glass and then moving the glass to a separate cutting surface is the preference of many.
• ·        Making pattern pieces with the space for the foil and tolerance already cut out is a preference of many copper foilers.

Each of these assistance methods are acceptable, although the more steps involved in translating the cartoon to the glass, the more chance of introducing inaccuracies.  The accuracy of the final piece depends upon the skill with which you can manoeuvre the cutter around the glass.  This requires practice. With practice, accuracy will improve.

Machines

Glass saws of several types are available to assist in getting accurate shapes.  Mostly they are narrow thin diamond coated blades or diamond coated wire.  The wire-based saw can cut tighter and more intricate shapes than the band saw can.  But you should think about the nature of glass before you get too intricate.  The breakage rate of intricate pieces in stained glass is relatively high, even in the early life of a piece.  In fused glass it is not so difficult as they normally are supported by a base piece of glass.

Accuracy in using these saws relates to:

• ·        Manipulation of the glass to follow the line exactly.
• ·        Permanency of the guiding lines drawn onto the glass.
• ·        Accuracy of the drawn lines.
• ·        Accuracy of the pattern pieces.
• ·        Allowing the machine to cut rather than forcing the glass into the blade.
• ·        Maintenance of the machine.
• ·        Maintenance of the blade or wire.

Your accuracy will increase in the use of hand scoring or machine sawing of the glass with experience.  But, the degree of your critical appreciation of your cutting results is directly related to the accuracy of cutting.  The more you say “that is good enough” the less quickly you will improve your accuracy.