How to remove margins from plot?

[P@u1]

Hi,

I want to display a plot without margins at the left and right sides.
I tried using

plot->axisScaleEngine(QwtPlot::xBottom)->setMargins(0., 0.);

plot->axisScaleEngine(QwtPlot::xBottom)->setMargins(0., 0.);

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but it doesen't change anything.

On both sides there is still free space which is not used by the plot.
How can I solve this?