Thanks Wolfgang. Clearly that fixes the problem. I also came up with 
another solution which avoids the need to define a MyChapterCommand, by 
first setting up the normal chapter as:

\setuphead
   [chapter]
[header=empty,alternative=middle,style=bold,numbercommand=\groupedcommand{}{\blank[2cm]},after={\blank[3cm]}]

and then setting up a mychapter as:

\definehead[mychapter][chapter]

\setuphead[mychapter][header=empty,alternative=middle,style=bold,numbercommand=\groupedcommand{}{\blank[2cm]},after={\blank[.5cm]}]

That gives me the result I am after as well as maintaining the style of 
the standard chapter head.

Julian

On 3/6/20 12:58 am, Wolfgang Schuster wrote:
> jbf schrieb am 02.06.2020 um 11:41:
>> Hi list,
>>
>> I am attempting to achieve, for every second chapter, to have only 
>> one line of space between the chapter title and the text that follows.
>>
>> I looked at the following example in the wiki:
>>
>> \setuppapersize[A6][A6]
>> \setupbodyfont[8pt]
>> \def\MyChapterCommand#1#2%
>>    {\vbox  to 4cm\bgroup
>>       {#1\hskip.75em #2}
>>       \vss
>>       \egroup}
>> \setuphead[chapter][header=nomarking, command=\MyChapterCommand]
>> \starttext
>> \chapter{test}  \input  tufte
>> \stoptext
>>
>> and presumed that I could adjust that to something like 1cm instead 
>> of 4cm.
>>
>> The problem is that when I try to process the original example, I get 
>> a fatal error at the line which reads \chapter{test} \input tufte.
>>
>> I'm not sure why that error, but that aside, would the 
>> \def\MyChapterCommand approach suggested above be the right way to 
>> achieve my purpose? In other words, I want the text that follows the 
>> chapter title to follow immediately for specific chapters, rather 
>> than the considerable vertical space that follows the default setup 
>> for chapter titles.
>>
>> Julian
>
> Change
>
>     \def\MyChapterCommand#1#2%
>
> to
>
>     \unexpanded\def\MyChapterCommand#1#2%
>
> or
>
>     \define[2]\MyChapterCommand
>
> Wolfgang