The secret for a glove-tight fit for trim corners is a coped joint. With this technique you can even make complex crown moldings fit without leaving gaps. http://www.familyhandyman.com/carpentry/trim-carpentry/how-to-cope-joints/view-all
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This handy little “cheat sheet” can be used on any crown molding project that requires inside and outside corners. Visit Dunndiy.com to learn more about how to measure, cut, and install crown moulding.
The Easiest Way to Add Trim to a Cabinet
Upgrade those builder grade cabinets by adding some molding to the cabinets.
4 Inch flat back foam crown moldings - Crown molding solutions
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exterior corbels and brackets - Google Search
CurveMakers Patented Arch Kits, Wood Arches, D-I-Y Arched Doorways and Openings, Interior Archways, DIY Arches, Curved Moulding and Trim
How To Cut And Install Crown Molding And Trim
The comprehensive DIY guide to cutting and installing crown molding & trim installation from the construction and home improvement experts.