On Wed, Jul 16, 2008 at 9:18 PM, Alan Stone
(1) \definefont[myChapterFont][myHeadingsFont sa 1.728] You could either use a real font name like 'Arial' or a symbolic name defined with \definefontsynonym like 'Serif', 'SerifBold', 'Sans', 'Dummy-Regular' etc. in the second argument of \definefont but not the name for a font collection defined with \definetype, in your case \definefont[myChapterFont][Sans sa 1.728] or \definefont[myChapterFont][DummyRegular sa 1.728]
So ( and considering the example at http://wiki.contextgarden.net/Chapters_headers ) I tried...
The example use the two symbolic names Regular and RegularBold which are defined as synonyms for Serif and SerifBold wich are itself will always work because they result in the current serif regular and serif bold style independant of the font. Regards, Wolfgang