First three rules I was taught:
1.) Most of the time - keep your sketches simple. Use placed features rather
than sketched features for holes, chamfers, fillets, and patterns.
2.) Make your rough sketch as close to the constrained size as possible
using the coordinate display in the status bar. This helps to prevent some
of the problems constraining the sketch.
3.) Use constraints first, before dimensions. Try to use constraints in a
way as to develop the sketch with as little dimensions as possible.
--
Phil Kenewell
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Gage Designer
North American Lighting, Inc.