Hour glass shapes, wasp waists, or those that are thinner
along the length than the ends, should be avoided as much as possible. They are difficult to break out from the
score. More importantly, they are an inherently
weak shape. The longer the piece is with the narrow part along its length, the
more likely it is to break; in cutting or in the long term, in the panel. However, these shapes are sometimes
unavoidable.
The principle to use in scoring and breaking out the glass is
to remove less glass than that you are retaining at each stage of the process.
This has consequences:
- · breaking the first score is the easiest
- · only a rough outline of the final piece should be scored and broken from the sheet
- · Relieving scores and breaks will be necessary. The number will depend on the relative thickness of the thin and thick parts.
You can make the first score and break of one side of the
shape from the main piece of glass – usually with little difficulty or need for
relieving scores. (1)
You then should score and break off the piece to be retained
from the larger sheet. Be sure to give a
margin for the final piece. (2)
Now score the other part of the hour glass shape. Do not tap the score. Begin gently to run of
the score from each end. Don’t worry if
the runs do not meet up. Do not tap to
make them meet up. (3)
If running the score from both ends is not enough to make
the run complete, you will need to use relieving scores. These scores can be like onion rings –
generally concentric curves running in the same sort of shape as the curve to
be broken out.
Or you can use the fish scale approach – overlapping crescents. These are most useful for deeper inside curves.
Or you can use the fish scale approach – overlapping crescents. These are most useful for deeper inside curves.
Either way, each score needs to be planned. Each relieving score should be smaller than
the width of the piece to be retained.
In general, this means the outer relieving scores can be wider
apart. As you approach the final shape,
the distance between the scores will need to be less and less. (4,5,6)
More information on scoring and breaking out concave curves can be found here: http://glasstips.blogspot.co.uk/2008/08/cutting-concave-curves.html
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