I subclass QwtPlot and create function to set minValue, maxValue and scaleEngine of the axis. Also I draw axis inside plot canvas. Here is relevant part of the code:
Qt Code: 
  1. void GeneralPlot::drawAxisInsideCanvas(){
  2.     QwtPlotScaleItem *scaleItemY =
  3.         new QwtPlotScaleItem(QwtScaleDraw::RightScale);
  4.     scaleItemY->setBorderDistance(0);
  5.     scaleItemY->attach(this);
  6.     this->enableAxis(QwtPlot::yLeft, false);
  7.     this->setAxisScale(this->yLeft,0,1);
  8.     this->setAxisMaxMinor(this->yLeft,0);
  9.  
  10.     QwtPlotScaleItem *scaleItemX =
  12.     scaleItemX->setBorderDistance(0);
  13.     scaleItemX->attach(this);
  14.     this->enableAxis(QwtPlot::xBottom, false);
  15.     this->setAxisScale(this->xBottom,0,100);
  16.     this->setAxisMaxMinor(this->xBottom,0);
  17.     this->updateAxes();
  18. }
  19.  
  20. void GeneralPlot::setXAxis(double xmin, double xmax, bool linear){
  21.     bool xlinear = dynamic_cast<QwtLinearScaleEngine*>(axisScaleEngine(xBottom))!=NULL;
  22.     if(xlinear){
  23.         setXAxisScale(xmin, xmax);
  24.         setXAxisLinear(linear);
  25.     }else{
  26.         setXAxisLinear(linear);
  27.         setXAxisScale(xmin, xmax);
  28.     }
  29.     this->updateAxes();
  30. }
  31.  
  32. void GeneralPlot::setXAxisScale(double xmin, double xmax){
  33.     setAxisScale(this->xBottom, xmin, xmax);
  34. }
  35.  
  36. void GeneralPlot::setXAxisLinear(bool b){
  37.     bool xlinear = (dynamic_cast<QwtLinearScaleEngine*>(axisScaleEngine(xBottom))!=NULL);
  38.     if(xlinear&&!b){
  39.         setAxisScaleEngine(xBottom, new QwtLogScaleEngine());
  40.     }
  41.     else if(!xlinear&&b){
  42.         setAxisScaleEngine(xBottom, new QwtLinearScaleEngine());
  43.     }
  44.     this->updateAxes();
  45. }
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GeneralPlot::drawAxisInsideCanvas() function is called in constructor. The problem is that sometimes axis is not updated, however plot canvas is updated. For example if I call :
Qt Code: 
  1. plot->setXAxis(1, 100, false) //1 - 100 log scale
  2. plot->replot()
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everything is fine, but if after that I call
Qt Code: 
  1. plot->setXAxis(-100, 100, true) // linear scale
  2. plot->replot()
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Axis is not updated, however plot with grid is already updated. If I resize plot window then axis updates. Everything works fine if I don't plot axis inside plot canvas (don't call drawAxisInsideCanvas() in constructor) then everything is fine. How shoul I make QwtPlotScaleItem to be updated after plot replot?