Then you did something wrong - when you enable grid lines for the minor ticks ( QwtPlotGrid::enableXMin()/!enableYMin() ) you will see grid lines for every minor tick.
But modifying attributes of the grid has no effect on number and positions of the ticks. This can be done modifying QwtPlot::setAxisMaxMinor and QwtPlot::setAxisMaxMajor - and of course by setting attributes for the corresponding scale engine.
Uwe
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