Cant't draw custom grid

[Uwe]

However, this doesn't solve my problem since I want aoutoscaling but with custom labels.

Setting custom ticks is the opposite of autoscaling - so this makes no sense.

But you can configure the autoscaler, that is part of the QwtScaleEngine for your axis. You also have QwtPlot::setAxisMaxMajor/setAxisMaxMinor to limit the number of intervals ( = ticks ) calculated by the autoscaler.

I assume I've missed something in the basic functionality of the QwtPlotGrid since it won't display my custom grid without the same fixed, custom scale...

Yes you do: the grid is responsible for the horizontal/vertical lines according to the scale ticks on the plot canvas. But it has nothing to do with the scales itsself.

EDIT: Hey! And while we're at it, could someone tell me how to change the color of the font in the scales?

Depends on which fonts you mean:

a) Each widget has a setPalette() method - so each QwtScaleWidget has a palette as well.
b) All labels used in a plot are QwtText objects, that can have their own font/color.

Uwe